[HN Gopher] Tesla shares 48V architecture with other automakers
___________________________________________________________________
Tesla shares 48V architecture with other automakers
Author : toomuchtodo
Score : 295 points
Date : 2023-12-07 15:10 UTC (1 days ago)
(HTM) web link (electrek.co)
(TXT) w3m dump (electrek.co)
| sitkack wrote:
| TIL that 42V fizzled out
| https://en.wikipedia.org/wiki/42-volt_electrical_system
|
| I welcome the move to 48V, as one gets lots of cross over
| synergies from the 48V telco standard.
|
| https://www.servertech.com/blog/48vdc-power-and-the-backbone...
|
| https://www.st.com/content/dam/AME/2019/developers-conferenc...
|
| https://www.maximintegrated.com/content/dam/files/products/p...
|
| https://www.infineon.com/cms/en/applications/information-com...
| mccoyc wrote:
| Agreed. 48V (actually -48V) has been used across telco central
| offices for decades.
| kurthr wrote:
| It's a really nice voltage with lots of support for batteries
| and up/dn conversion hardware.
|
| It's also right at the edge of what is human safe. You can
| burn yourself and blow up cables, but it's very difficult to
| electrocute yourself (afib or muscle seize) without lots of
| wet contact.
|
| https://incompliancemag.com/article/experiments-of-dc-
| human-...
| jacquesm wrote:
| Indeed, I'm aware of only one recorded death by
| electrocution at 48V, iirc it was a Swiss radio amateur
| that had done a bunch of gardening sat down sweaty in a
| metallic chair and reached for the one switch of his set.
| Probably there were other contributory causes as well, I've
| been zapped multiple times from much higher voltage sources
| (that could have easily supplied the power required) and
| lived.
|
| I can't find a reference for that Swiss case though. I'll
| keep looking.
| IgorPartola wrote:
| I assume if you didn't live from those zaps you wouldn't
| be here making this comment.
| jacquesm wrote:
| Haha, fair point, yes, indeed. The most clear form of
| survivorship bias, thank you for pointing it out.
| firebat45 wrote:
| How exactly do you define a negative voltage unless you are
| using some other voltage as a reference?
| dragontamer wrote:
| Label the power pin+ GND and the power pin- becomes -48V
|
| Voltages are all relative. It's like saying 'How do you get
| a height difference of 10 feet by digging?'
|
| Well, you dig and then label the initial level as +10 feet,
| and redefine the bottom of your hole to be ground.
| Kirby64 wrote:
| No. In telco, the -48V is referenced against ground, like
| the physical ground. If you're isolated, you can do this.
| but they would still need to be referencing the 'ground'
| to something ... likely the negative side of the main
| battery pack.
|
| The reason why -48V is used is because it is provided as
| a bias voltage to give wiring cathodic protection, to
| prevent corrosion of telecom infrastructure. If you used
| 48V, it would not work. You need a negative voltage
| referenced against ground.
| applied_heat wrote:
| Ground positive terminal of battery string instead of
| grounding negative terminal.
|
| I see this more often on European stuff
| bluGill wrote:
| Generally with respect to ground. There are many good
| reasons to connect your power system to ground and so this
| is commonly done. (there are pros and cons to connecting to
| ground, but it gets complex fast)
| myself248 wrote:
| It is with respect to ground, the positive pole of the
| battery is connected to ground.
|
| The telegraph system figured this out very quickly. Most
| water in nature has at least a bit of salt in it, which is
| present as positive sodium ions and negative chloride ions.
| By making the outdoor wiring negative with respect to
| ground, the chloride ions are repelled, and such wires
| corrode much more slowly than those that're positive with
| respect to ground.
|
| Since most of the telegraph network, later the telephone
| network, is outdoors, this is a pretty big deal.
| thebruce87m wrote:
| > that're
|
| First time I've ever seen this typed
| hinkley wrote:
| What're you talking about?
| denysvitali wrote:
| I guess he refers to the shortening of "that are" into
| that're
| DennisP wrote:
| I think you're missing your parent's joke.
| magicalhippo wrote:
| It's a matter of perspective.
|
| You tie one of the leads to earth (literally grounding
| it)[1], leaving the other non-grounded. Depending on if you
| tie the negative or the positive lead to ground, you get
| 48V or -48V with respect to ground. As long as the
| potential between the most positive lead and the least
| positive lead is 48V, the circuit itself doesn't care.
|
| As mentioned here[2], the reason for grounding the positive
| lead is to prevent galvanic corrosion[3] destroying the
| buried copper.
|
| [1]: https://www.bicsi.org/docs/default-source/conference-
| present...
|
| [2]: https://www.poweringthenetwork.com/uncategorized/negat
| ive-48...
|
| [3]: https://en.wikipedia.org/wiki/Galvanic_corrosion
| hinkley wrote:
| Apparently in cars it's weirder. Wire it one way and the
| wiring corrodes. Go the other way and the body corrodes.
| bloggie wrote:
| Voltage is a measure of charge difference so there must
| always be a reference, usually the reference is 0 V.
| londons_explore wrote:
| I don't think they'll be able to use much of that with their
| 48v PoE ethernet standard...
| SigmundA wrote:
| As mentioned in the 42v article they went with that due to 48v
| nominal being too close to 60v max on alternator/fully charged
| which is the limit shock hazard.
|
| Not sure what chemistry/cell count will be for the 48v battery
| (which I assume it has) but 48v could mean 13s - 16s packs.
| GuB-42 wrote:
| Are you telling us that 42 wasn't the answer after all?
| DennisP wrote:
| Nah you have the wrong question. You'll need a bigger
| computer.
| xjlin0 wrote:
| It is, just be patient and the battery will be drained to 42V
| eventually.
| pupppet wrote:
| Do more stuff like this, Elon. I really don't like not liking
| you.
| r3d0c wrote:
| weird comment... maybe we shouldn't feel the need to idolize
| humans...
| flappyeagle wrote:
| It's ok to like people
| rnk wrote:
| We humans are all terrible on some level (except my mom, she
| was a saint), but if you have enormous power, you can help or
| hurt a lot of people based on your actions. Musk has a lot of
| power. He must be a terribly lonely person, not knowing if he
| can trust anyone or they just want something from him.
| firebat45 wrote:
| Nobody knows if they can trust anyone, not just rich
| people.
| argiopetech wrote:
| Right, but it's a lot easier when you don't have anything
| someone else might want, much less a billion or more
| things.
| davidcbc wrote:
| He could give away 99.99% of his wealth, still never have
| to work another day in his life, and be much less of a
| target if he wanted to. Boo hoo the poor guy who has more
| money than almost anyone has ever had in the history of
| the earth has problems
| DarmokJalad1701 wrote:
| If he gave away 99.99% of his wealth, that would tank the
| retirement accounts of millions of people, possibly have
| his life's work be taken over by some hedge fund
| ("introducing the Tesla Model V8, now with extra vroom-
| vroom!"), and then get sued by shareholders for the
| remaining 0.01%.
| bluGill wrote:
| True, but it isn't worth a thief's time to steal things
| from me, so I'm less a target of dishonest people. Not
| zero target, but not a big target. Rich people because
| they have money are a larger target. Nobody would seek to
| marry me for my money - filing for divorce as soon as
| enough time has past to make it look like that wasn't
| their goal - a small number of people would do that and
| they seek out rich people.
| SilverBirch wrote:
| Hi, excuse me. Just want to say, don't appreciate you
| rounding me up with the anti-semites. "We humans". No -
| those anti-semites, and us reasonable people. Wouldn't like
| to mix with them thanks. You can make whatever excuses you
| want for him, but that's what they are, excuses.
| erupt7893 wrote:
| This is silly, don't stand on some high horse. If you
| don't think you have the capability to be unreasonable,
| you are delusional. Every single person on this planet is
| capable of evil, but majority luckily see that as a path
| that ends badly.
| SilverBirch wrote:
| I think there's a bright bold line between me and the
| anti-semites and I think that you're doing the work of
| the anti-semites to pretend there's not. Everyone is
| capable of evil. Some people actually do evil things
| though and some people don't. The issue here isn't what
| people are capable of, it's what they're doing, and Elon
| Musk is endorsing crackpot anti-semitism on the platform
| he owns in the aftermath of the largest attack on Jews
| since the holocaust.
| itishappy wrote:
| Is "he's not doing enough cool stuff" really the root of your
| dislike of Elon?
| jandrese wrote:
| Don't worry, it will only be a matter of time before he
| retweets a neo-Nazi and you can go back to hating him.
|
| Some people have way too binary a view of other people. In real
| life there are rarely outright villains or complete saints.
| Everybody is a mix of greys. You don't have to agree with
| _everything_ a person does or says to appreciate their work.
| pupppet wrote:
| Retweeting neo-nazi content is no shade of grey.
| intrepidhero wrote:
| Why would a car need a 48V system for accessories? In general the
| things a car's 12V system powers have gotten less power hungry
| over time (LED's, heat pump) and in particular, an EV loses the
| highest power electrical device on the 12V bus, the starter. The
| typical equipment used for the entertainment and control systems
| are going to be much more available with 12V supplies, just
| because that's the industry standard.
|
| Obviously the traction system is using much, much higher
| voltages.
|
| The article cites "complexity" of the wiring harnesses, which is
| nonsense. The wires might get a little smaller, but not by a lot.
| Like I said, the 12V bus in an EV isn't driving a bunch of high
| power stuff. (Is it? Am I missing something?)
|
| The one place I can imagine it helping is for driving inverters
| so you can provide AC outlets for laptops, power tools, etc.
| pgeorgi wrote:
| https://de.wikipedia.org/wiki/Bordnetz#48-Volt-Bordnetz_im_A...
| explains (a bit) why German car makers are using 48V since
| ~2016 (in addition to the still existing 12V system, which
| seems to be the difference with Tesla, which went 48V-only).
|
| DeepL translation:
|
| The 12 V electrical system can barely cover the power
| consumption that modern vehicles need for their comfort
| systems. The "static" consumers completely overload the
| alternator, which provides up to 3 kW of power, especially at
| low temperatures.[12] The battery power is not sufficient for
| additional dynamic consumers, such as powerful electrically
| driven compressors.[13]
|
| For this reason, a proposal was made at the end of the 1990s to
| install a 14 V/42 V electrical system in motor vehicles.[14]
| From 2001, Japanese manufacturers and General Motors launched
| hybrid vehicles with this electrical system on the market.[15]
| Although Daimler-Chrysler was one of the co-initiators of this
| concept, it was not used in Germany. One reason for this was
| that it did not appear possible to demonstrate a corresponding
| utility value to customers for the necessary additional
| price[14].
|
| Instead, since 2010, German car manufacturers have favoured the
| solution of providing a second 48 V electrical system to
| supplement the 12 V system.[9] Since 2016, the first series
| applications of 48 V electrical system components have been the
| operation of the electric compressor and the electromechanical
| roll stabilization in the Audi SQ7 4.0 TDI and Bentley
| Bentayga. Both are based on the same platform.
|
| Translated with DeepL.com (free version)
| intrepidhero wrote:
| A split 48/12 system makes a lot more sense. Run the
| heater/heat pump, power steering, coolant pump, etc on 48V
| and keep entertainment and controls on 12V.
| bryanlarsen wrote:
| Computer chips use ~1.5V or so these days. Why go
| 48V->12V->1.5V when you can go 48V->1.5V directly? If it's
| more efficient to use an intermediate voltage, you can
| choose the most efficient intermediate voltage internally
| rather than using 12V.
| bluGill wrote:
| There is a lot of off the shelf 12V equipment you can
| buy. Plus even more that is sitting in garages ready to
| be installed in the next vehicle. Cars are manufactured
| in enough quantity that it would only cost $0.01 per
| vehicle to design it (plus parts costs which are probably
| the same), but that is still a few million to the bottom
| line if they use the same 12 volt radio. Add to that that
| ICE cars everywhere have 12 volt starters, and you can
| buy 12 volt jump start kits: when (not if!) a battery
| fails to start the ICE you better be able to jump start
| it from a 12 volt battery - this is a safety issue.
|
| Tesla doesn't have ICEs, so the safety concerns are lost
| on them. Thus all 48 volt makes some sense. They still
| need something for all the accessories people have.
| taylodl wrote:
| Because we already have the 12V infrastructure and part
| supplies in place. You're disrupting things for no
| benefit. We've been running split 24V/12V systems for
| decades now in automotive applications. It's not that big
| a deal to change that to 48V/12V systems as many European
| car manufacturers have done.
| bryanlarsen wrote:
| No benefit? I've seen estimates of $1000 in reduced cost
| due to reduced copper wiring, and more importantly the
| labor required to string that wiring.
|
| Modern phones charge on 48V these days, so 48V parts are
| extremely common & cheap.
| pgeorgi wrote:
| I'd fully expect other car makers to move to an exclusive
| 48V setup at some point. They just do it gradually: For
| the new model a part is replaced by its next-gen
| successor that is incompatible anyway? Put it on the 48V
| bus. Repeat until the 12V system is done away with - or
| force the issue when there are only a few components
| left, or downstep the 48V to 12V right in front of them,
| once that's cheaper than keeping the remaining 12V
| system.
| bryanlarsen wrote:
| It'd be cheaper to delete the 12V bus entirely and add
| 48V -> 12V converters in front of legacy components, even
| if they needed several dozen of those converters.
| panick21_ wrote:
| I expect Tesla to still have a few components like that
| in the car.
| imp0cat wrote:
| Isn't that the point of the article though? That they run
| everything on 48V?
| panick21_ wrote:
| I think all the wires/communication are but some of the
| devices attached are lower then 48V, some very low
| voltage, and some might be 12V. We will see when its
| taken apart.
| jabl wrote:
| > I've seen estimates of $1000 in reduced cost due to
| reduced copper wiring
|
| What about aluminum wiring? Lighter, cheaper, though
| bulkier than equivalent copper. Aluminum wiring got a bad
| rep back in the day, but it seems with current electrical
| aluminum standards it supposedly works pretty well.
| atoav wrote:
| In sotuations where it is about space you wouldn't choose
| aluminum. Also afaik most automotive wiring that is
| certified is copper. Going from copper to aluminum means
| you will have to put bigger crossections in. This is more
| weight and more space.
| myself248 wrote:
| Aluminum is hell to terminate. It basically requires
| ultrasonic welding; every trade-show has folks hawking
| various crimp terminals that're meant to break through
| the surface oxides during the crimp cycle, but not a
| single automaker has been swayed enough to use it on
| normal wiring.
|
| The reliability concerns really add up with flexing
| fatigue, too. It's one thing to put aluminum wiring in a
| house where its only flex is due to thermal expansion,
| and it has a hard enough time coping with that it's still
| a special category in home insurance, to say nothing of a
| vehicle that's going to spend the next ten-plus years
| bouncing over the road.
|
| Furthermore, you basically can't modify aluminum wiring.
| In-line splices and solders are virtually impossible.
| While that's irrelevant for manufacturing, it hits the
| aftermarket pretty hard, including dealer mods, and of
| course, dealer repairs. That can be worked around but it
| would require communication between branches who don't
| normally talk, and it just adds friction to any possible
| aluminum migration.
|
| I've seen aluminum in a single very-heavy-gauge battery
| cable for a car that put the battery in the back, with
| ultrasonic-welded terminals on both ends, and that's
| _it_. Everything else in that car was copper.
| taylodl wrote:
| What you may have saved on wiring is going to be offset
| by the increased cost of the battery (I'm seeing 2x-3x
| cost) and the fact you now need a much beefier alternator
| which is going to have its own cost.
|
| You'd think if it were a slam dunk then the bean counters
| would have insisted on a transition to 48V years ago.
| jandrese wrote:
| Total current consumption should be about the same (or
| even less, thanks to lower losses at 48v), so I'm not
| sure why would you would need a "much beefier"
| alternator. It will need different windings, but overall
| it should be about the same size and cost.
| taylodl wrote:
| Once you've introduced a 48v system engineers will find
| ways to use that extra power. They've been spending
| decades carefully managing that power and making
| compromised. Now they won't have to. So yes, you're going
| to need a higher output alternator to keep the 48v
| battery charged due to the increased load.
| Kirby64 wrote:
| What modern phone charges at 48V? I'm not aware of any
| that charge at even 20V, outside of a couple of gimmick
| devices. No Samsung or Apple phone charges at anywhere
| close to that, that's for sure.
| smileysteve wrote:
| What modern phone charges at 12v?
|
| Most phones charge at 5v. Modern USB-C chargers can
| charge between 5v and 20v based on configuration.
|
| Buck converts and regulators are cheap and small these
| days.
| nikau wrote:
| Most phones charge higher than 5 volts these days
| turtlebits wrote:
| Samsung phones can fast charge at 15v/3a (45W).
| Kirby64 wrote:
| 12V isn't a 'standard' USB-PD voltage, so pretty much
| none of them. Tons of phones charge at 9V, though. And
| some use 15V.
|
| The regulators/buck converters you speak of are inside
| the phones these days. They want a higher voltage even if
| the battery itself is 3-4.2V, so losses from cabling are
| lower and you don't need a special 5A cable to handle
| charging at the fastest rate.
| bryanlarsen wrote:
| I believe Qualcomm's QuickCharge 5 can use the full 48V
| of USB-PD. Given it allows 100W, I certainly hope so.
|
| Regardless, QuickCharge 3 is 20V and it's been in a lot
| of phones since it was introduced in 2016.
| SkyPuncher wrote:
| You can run smaller wires through the vehicle then down voltage
| on device.
| CamperBob2 wrote:
| _Like I said, the 12V bus in an EV isn 't driving a bunch of
| high power stuff._
|
| Take a look at the fusebox in any modern car, EV or not. (There
| will most likely be more than one fusebox.)
|
| You'll see lots of 20A, 30A, 40A parts, some even larger.
| Running those circuits on 12 volts takes more copper than you
| probably think it does. More copper and beefier (read: _much_
| more expensive) connectors. The move to 48V is frankly overdue.
| rnk wrote:
| Just to add the basic idea, the amount of power is amps *
| volts. So to carry the same amount of energy with a higher
| voltage, you can you use less amps. The amount of amps impacts
| how big the wires are, lower amps need smaller wires and that
| means less space for wires but more importantly less weight of
| the wires. There is a lot of wiring in a car. Tesla claims this
| could be 1/4 the amount of copper wiring in an article, below.
|
| This article describes a bit about this, but also says
| something I never heard, that there were 6v auto systems in the
| 1960s. https://www.mining.com/new-tesla-low-voltage-system-a-
| big-de...
| bluGill wrote:
| 6 volt autos were going out of style in the 1950s. They did
| last into the 1960s, but they were already rare by then.
| bokohut wrote:
| It may help some also to know what an amp actually is:
| 6.241x10^18 protons or electrons per 1 second of time passing
| a certain point. A single Amp is equal to 1 Coulomb and 1
| Coulomb has 1 Joule of energy. I share this from my personal
| documentation in comprehension of understanding the unseen
| resulting from a device I am building to solve a personal
| energy storage problem. All open knowledge certainly but
| graphing these relationships into a visual depiction of the
| correlation has greatly assisted when talking to others that
| have ZERO knowledge about energy and power. Humans are nearly
| all 100% visual so explaining it with pictures presents A LOT
| of AHA moments for those without such comprehension.
|
| The inverse relationship between amps and volts can also
| help: 50 volts * 24 Amps = 1200 Watts 100 Volts * 12 Amps =
| 1200 Watts 120 Volts * 10 Amps = 1200 Watts 150 Volts * 8
| Amps = 1200 Watts 200 Volts * 6 Amps = 1200 Watts 240 Volts *
| 5 Amps = 1200 Watts 360 Volts * 3.333 Amps = 1200 Watts 480
| Volts * 2.5 Amps = 1200 Watts 600 Volts * 2 Amps = 1200 Watts
|
| Stay Healthy!
| jabart wrote:
| Power steering pumps are electric and have one of the largest
| wires in my truck. With an EV you also have a heat pump, maybe
| a heater, coolant pumps now that you don't a constant spinning
| pulley, windows, lights, headlamps, power doors, seats, radio,
| amplifier, small PC, etc.
|
| From the article "Switching to 48V architecture alleviates a
| huge number of challenges automakers are facing with 12V. The
| biggest one, though, is complexity: You need far less complex
| wiring harnesses to power all your vehicle systems"
|
| My take is that 12v requires almost a dedicated power line for
| each part, while a 48v could run to a bus line that gets
| tapped. 48v might be something that divides easier with the
| battery pack, and drops the 12v battery.
| intrepidhero wrote:
| I hadn't connected the dots that all the various pumps (and
| fans) have to switch from mechanically connected to the
| engine via the accessory belt to electrically driven. That's
| a fair point.
| smileysteve wrote:
| It has been optimal to run accessories electrically for ICE
| already for several reasons. It has been difficult based on
| some of the loads on a 12v battery (agm has really helped
| this)
|
| - Start stop is smoother (and more available) without
| accessories
|
| - Cooling a turbo after the motor is off - true for the
| engine as well, heat soak on water pump off can go ~20f
| over the thermostat
|
| - Brake Boosting without a vacuum (Valvetronic or Hybrid)
|
| - Air Conditioning at idle
| lizknope wrote:
| > Power steering pumps are electric and have one of the
| largest wires in my truck.
|
| Most new cars don't have hydraulic power steering systems
| anymore and use an electric motor for power steering. It
| improves fuel economy as well but the steering feel is
| generally worse than a hydraulic power steering system.
| fasteddie31003 wrote:
| Anything drawing over 250 watts is going to need over 12 gauge
| wire. I put a 2200 watt inverter in my truck and I needed to
| put 4/0 gauge cables to it which are huge. 48v would mean I
| could have gotten away with only 8 gauge wire.
| adolph wrote:
| Here is an explainer:
|
| https://youtu.be/ky1Z2klPalw?t=573
|
| Transcript:
|
| _. . . a little bit about electrical electrical engineering um
| you don 't need to know a lot but just a little bit uh we'll
| understand that you actually want a higher voltage in order to
| reduce the resistance losses._
|
| _So the heating in any wire is the current is the square of
| the current. So if you 're trying to get a particular power
| rating through then as you increase the voltage you can
| decrease the current. Voltage times amperage equals your power.
| To hold power constant, the heating is is proportionate to the
| square of the current. So you want to raise the voltage in
| order to lower the current thus lower the heating in the wire._
|
| _And the net effect being that you can have much thinner
| wires, then as you raise the voltage you can you can drop the
| the the thickness of the wires. You can have much you can use
| much less, in a nutshell. You can use much less copper and the
| wire harness weighs much less as you raised the voltage._
| martythemaniak wrote:
| The savings in terms of weight and efficiency are actually
| significant. This was covered in Tesla's investor day
| presentation earlier in the year:
|
| The section on electronic architecture (~10min):
| https://www.youtube.com/live/Hl1zEzVUV7w?si=-Vz0gKT5YDbtrG9V...
|
| The sub section (~4min) on 48V in particular:
| https://www.youtube.com/live/Hl1zEzVUV7w?si=shfI2vEz9taTLSm7...
| londons_explore wrote:
| Some devices in a car are still pretty power hungry. Eg. The
| blower motor for the fan (typically 800 watts = 70 amps @12v).
| Heated rear screen (240 watts = 20 amps). Window motors are
| pretty powerful too.
|
| End result is you need a lot of fairly chunky cables to power
| those things.
|
| And the price of copper has been steadily climbing since 1960 -
| unlike other commodities which have been getting easier and
| easier to extract with more automation in mines.
| londons_explore wrote:
| Most MOSFETS are 50 volt rated. 50 volts is a sweet spot for
| switching the most powerful load with the smallest and cheapest
| switch.
| KaiserPro wrote:
| if you're switching 48v, you'd want a mosfet rated for way
| more than 50v. On a car you'd want 200% headroom at least.
| londons_explore wrote:
| With totally uncontrolled bus capacitance and inductance,
| sure.
|
| But when you're using the same bus for Comms you need to
| have control of high frequency spikes, and low frequency
| spikes are easily handled by a bidirectional DC/DC.
| Therefore I could imagine peak to peak ripple on this bus
| to never exceed 1 volt.
| KaiserPro wrote:
| > Therefore I could imagine peak to peak ripple on this
| bus to never exceed 1 volt.
|
| https://www.quanterion.com/wp-
| content/uploads/2014/09/MIL-HD... disagrees.
| mauvehaus wrote:
| Not that anyone is going to stick a plow on a Cybertruck, but
| holy shit is the hydraulic pump on one of those a huge current
| draw. It's 4AWG wire on mine. The battery is kind of
| marginal[0] and when I raise the plow, the volt meter goes down
| to 7-8 volts if the engine's at idle and the alternator can't
| supply the needed current. Gunning the engine improves the
| situation somewhat, but wow, was that an eye opener.
|
| [0] _Everything_ on that truck is kind of marginal, actually.
| If you aren 't plowing for money, plow truck is the last stop
| before the big parking lot in the sky.
| bryanlarsen wrote:
| Most of the residential snow clearing outfits around me use
| plows and blowers on Kubota tractors. Probably part of the
| reason is so that can use PTO hydraulics...
| bluGill wrote:
| There are pros and cons. Snow plows beat on a the vehicle -
| which is why plows are the last thing a truck does before
| you quit using it. Highway departments will use a dump
| truck mounted plow because the frame of the dump truck can
| take the beating (that they can put salt on the dump truck
| is a very useful side effect). Tractors are designed to
| pull plows through dirt which also beats on them, and so
| tractors can stand up to snow plows better than a truck.
| However tractors are slower and so cannot work for on road
| work. PTO and hydraulics are useful as well.
| Filligree wrote:
| You don't use custom-designed vehicles? I'm used to
| snowplows being these massive, reinforced vehicles that
| look like they could take on a tank.
| mauvehaus wrote:
| I haven't a clue what you're describing. Do you have a
| picture? Also: where do you live, and how much snow do
| you get?!
| mrep wrote:
| Not OP, but here in park city UT, we average ~21 feet of
| snow a season and got an epic 51 feet last season!
|
| I normally see dump salting trucks with plows that
| plow/salt the roads during snow falls and then we have
| cat bulldozers that later come pick up the snow and move
| it into dump trucks to be hauled away.
|
| Video of the cats: https://www.icloud.com/attachment/?u=h
| ttps%3A%2F%2Fcvws.iclo...
| Filligree wrote:
| Northern Norway. But it isn't snowing right now -- and
| also I'm in Ireland -- so can't do.
| bluGill wrote:
| I've never seen that in Minnesota. They are attachments
| to a dump truck or road grader.
| bryanlarsen wrote:
| Yup, the tractors are for driveway work. For road work
| uses the dump truck mounted plows you describe.
| bryanlarsen wrote:
| In the case of the cybertruck, the windshield wiper motor to
| drive that massive 4 foot wiper blade is 5hp and would require
| 300 amps at 12V. That's larger than a starter motor.
| bluGill wrote:
| Larger in what way? A starter can draw more than 300 amps in
| some cases. However a starter only needs to run for a few
| seconds and then get plenty of time to cool off. You can burn
| out a starter if you crank the engine for too long. By
| contrast a windshield wipers needs to run for hours when you
| are driving in the rain, and thus needs to be larger to
| dissipate all the heat. (starters are also typically series
| wound DC motors which are also smaller, they work great for
| starters but not for most other motor applications)
| PinguTS wrote:
| What many people underestimate is all the comfort stuff we have
| and use in modern vehicles. Most of the utilizes some sort of
| electric drive. Any electric drive requires power: * Power
| sliding windows * Power seats * Electric trunk * Power sliding
| roof * Electric mirrors
|
| Also other stuff: * heated back window * heated front window *
| heated seats * heated steering wheel
|
| Also the lights, even when they are LED they still draw a lot
| of power: * front lights, * back lights. * surrounding lights *
| comfort lights
|
| That is just of few devices. Just look into all the comfort in
| a modern (luxury) vehicle.
| panick21_ wrote:
| There is a lot more. There is a huge amount of safty
| equipment and sensors in modern car. That stuff that is not
| seen but its there as well.
| tshaddox wrote:
| > Why would a car need a 48V system for accessories? In general
| the things a car's 12V system powers have gotten less power
| hungry over time
|
| It's not primarily about delivering more power, is it? I
| thought the point of higher voltage is that _for a given power_
| the wires can be smaller.
| bluGill wrote:
| It can be both. Higher voltage allows longer small wires,
| and/or more power on the same wires. Depends on what the car
| needs. If it is just a few lights on the back of the car you
| are looking for smaller/cheaper wires. However if you are
| looking to put something power hungry in back (work trucks
| have a lot of needs around this) the higher voltage allows
| the same wires to deliver more power.
| myself248 wrote:
| Hi, automotive electrical is my job.
|
| There's quite a bit of very thick wiring in a car, not just the
| starter wire, but boring stuff like audio amplifiers, rear
| window defrosters, power seat motors. Those things don't draw a
| ton of power, like maybe just a few hundred watts, but at 12
| volts even modest powers require extraordinarily thick wires,
| especially when you account for bundle derating.
|
| This requires large terminals, which requires larger
| connectors, and there's the complexity, because MOST of the
| wiring in the car is just signals, or low-power stuff, which
| can run over thin wires and small terminals. (Minimum size is
| limited by mechanical durability rather than electrical
| conductivity.) Making a "hybrid" connector that has a couple
| large cavities for large terminals, and a bunch of small
| cavities for small terminals, is a pain. Having separate
| connectors for heavy power and for signals introduces more
| assembly work and negatively impacts testability. The wires
| have different stiffness and bend behaviors, they exert
| different amounts of force on weather seals, they have to be
| terminated on different machines at different points in the
| assembly process.
|
| By allowing power wires to be nearly as thin as signal wires,
| you can use simpler connectors with unified terminals.
| Manufacturing gets simpler, harnesses get lighter, assembly
| gets faster and easier.
|
| Weight is also a huge deal, every ounce counts. There's upwards
| of 100 lbs of wiring harness in most cars, more in larger or
| premium models with a lot of accessories. If half of that
| weight is signals and won't change with voltage, but the other
| half is heavy power circuits that'll get 4x thinner at 48v,
| it's significant weight savings.
|
| Furthermore, switching heavy current means massive relays or
| FETs and the heatsinks thereon. If you can reduce the current,
| those components get lighter too. Audio amplifiers get lighter,
| speakers get lighter (stupid heavy-wound 2-ohm speakers to get
| reasonable volume out of low voltage drive? Nah, use standard
| 8-ohm now that you have real voltage at the amplifier!), all
| sorts of things get lighter.
|
| That's all in addition to the electric power steering already
| mentioned by others. EPS can easily move 1kw for short periods,
| and has stupidly huge wiring to do that at 12v. It's still
| chunky at 48v, but a lot less so, and can use more common
| terminals and connectors. Replacing a hand-assembled bolted
| connection with a machine-crimped and clicked-together
| connector improves reliability or reduces testing process
| overhead.
|
| It's really significant, and it's embarrassing that the
| industry fell flat on its face in the late 90s last time they
| tried. Here's hoping this takes off.
| panick21_ wrote:
| Awesome to hear from an expert. Im looking forward to some
| teardowns to see how the set this all up.
| mcguire wrote:
| The rumor I heard was that the higher voltage resulted in
| lower switch lifetimes. Any truth to that?
| cogman10 wrote:
| Yes, but not meaningfully. The higher the voltage you get,
| the more arching there is when a relay trips (also depends
| on if there's any sort of inductive load, think the sparks
| you see when you unplug a vacuum without turning it off).
|
| But when you think about the impact that has on switches
| and relays, realize that in your own home you have 120V
| controlled by switches. Very cheap switches last decades
| (though admittedly not switched as often as something like
| a blinker).
| myself248 wrote:
| Ahh, no.
|
| AC is fundamentally different from DC when it comes to
| arcing behavior, because it has zero-crossings. If a
| switch arcs while switching AC, the arc goes out 1/120th
| of a second later. An arc would have to be pretty
| enormous to have enough thermal mass to remain ionized
| long enough for the next half-wave to re-energize it and
| sustain it. (HV AC transmission and distribution tends to
| have SF6-filled switches for this reason.) But around the
| house, your AC switches are really simple because they're
| not moving anywhere near that much power. And
| statistically, some fraction of switch openings happen
| with near-zero instantaneous current anyway.
|
| DC, by comparison, is brutal to switch. It doesn't have
| zero crossings, so the arc has to be blown out by the
| design of the switch. That means nice wide contact
| openings, and on really large ones, magnetic blowouts to
| divert the arc into chutes that cool it.
|
| If you look at a switch datasheet.... pulling up a
| randomly-selected one from Digi-Key now.... https://mm.di
| gikey.com/Volume0/opasdata/d220001/medias/docus...
|
| Look at the cycle ratings. It has a bunch of different
| ratings depending on the contact form (some that're
| forced apart, some that're sprung apart), but in all
| cases, the DC rating is equal or much lower current than
| the AC rating. And the DC ratings only go to 24V, this
| switch IS NOT RATED for use at 48VDC at all, despite
| happily going to 250V when switching AC.
|
| So, if you're comparing apples to apples, if you had
| 48VAC for instance, that would be easier to switch than
| 120VAC. (At constant current, that is. If you want to
| move the same power, you need more current at the lower
| voltage, and it gets harder again.) But DC is oranges.
|
| Yes, switching 48VDC is harder than switching 12VDC, but
| only at constant current. And it may require _different_
| switches than 12VDC. Given that you only need a quarter
| as much current to move the same power, it's still a net
| win, but it's not at all comparable to switching AC.
| Kirby64 wrote:
| You're correct in all of that in regards to mechanical
| relays, but none of this matters for solid state devices.
| I'm not aware of any actual mechanical relays in Tesla's.
| They do have contactors for the HVDC connections, but
| that's about as close as you get to relays. Hell, they
| don't even have fuses; they use self reset-able 'soft'
| fuses.
|
| You have to worry about shutting down current quickly
| (i.e., inductor flyback), but that's a pretty trivial
| problem to solve.
| mcguire wrote:
| I thought about those, but the 120v AC switches are
| gigantic beefy things compared to most automotive
| switches.
| tgsovlerkhgsel wrote:
| Would there actually be switches switching 12 or 48V in a
| modern car, especially a Tesla? I'd expect the switches to
| only switch signal voltage/current, and power electronics
| (MOSFET? no idea, not an electrical engineer) switching the
| actual loads.
| stephen_g wrote:
| That's right, the switching concern was in older cars
| where they were switching the 12V straight up, so that is
| a reasonable point for why they never switched to higher
| voltages, but yes, in most modern cars (and basically all
| EVs) buttons and switches would mostly all just be
| signalling electronic units to do the actual switching.
| tootie wrote:
| Is Tesla's design here actually innovative or really just
| they're the first ones to put together a bunch of stuff that
| everyone knew and hasn't had the wherewithal to implement?
| ricardobeat wrote:
| > or really just they're the first ones to put together a
| bunch of stuff that everyone knew
|
| Thats what 80% of "innovation" is, with the exception of
| applied science fields.
| myself248 wrote:
| I haven't seen the document being referred to elsewhere,
| but I highly doubt that there's anything fundamentally new
| under the sun. The industry tried this before but got stuck
| in a first-mover-disadvantage situation, which doesn't
| affect Tesla as severely because they have relatively few
| parts in common with other cars in the first place.
|
| So put me down in the "wherewithal" column.
|
| That's not to discount it at all. There are some real
| challenges; most automotive fuses for instance, are only
| rated for 32-volt operation. (Fuse voltage has to do with
| the length of the gap opened when the element blows, and
| the structure's ability to withstand or staunch any arcing
| that may happen.) Telephone fuses would work here but
| they're not exactly cost-optimized, I'd love to see what
| they do in this space.
|
| Switch and relay contacts too, may need different or
| thicker coatings to reliably break 48 volts at the number
| of cycles needed, but they'll be doing so at much lower
| currents so I think it's a net win. (Contact wear isn't my
| field of expertise, though.) However, mechanical switches
| are decreasingly relevant in the power path anyway, and
| FETs will definitely do better with the lower currents.
|
| One thing I saw talked about last time, which is completely
| irrelevant now, is alternator load-dumps. You know, due to
| the lack of alternators. But in the past, with an accessory
| belt spinning an alternator, the power produced by the
| machine was dictated by the current in the field winding.
| Regulating the output was a simple control loop, sensing
| the system voltage and servoing the field current
| accordingly. The field winding has significant inductance
| so its field can't change quickly, but with a big battery
| sitting on the bus that didn't matter. However, if the
| battery lead became disconnected, and the power draw on the
| system decreased, the alternator would suddenly be
| producing too much current and unable to rapidly reduce its
| field, and with no battery there to absorb the overage, the
| result is the system bus voltage spiking as high as 120
| volts, or at least that's what the load-dump test spec says
| you have to withstand for 400 milliseconds. In practice
| with incandescent bulbs and some other linear loads around,
| they'll typically clamp the transient to 40 volts or so,
| but that's still pretty harsh for stuff that's working at
| 14-ish.
|
| The concern was that a 48-volt alternator could produce
| some truly terrifying load-dump transients. (Although I
| think this is also overblown; it's running at lower current
| so the field winding would be weaker and should be able to
| decrease its field faster, no? Hmm. I should do some
| math...)
|
| But now that the 12v or 48v is produced by an electronic
| DC-DC converter running from the traction battery rather
| than an alternator spun by the engine, it's completely
| immaterial.
| jpm_sd wrote:
| Littelfuse makes some nice 58V rated blade fuses.
| brandonagr2 wrote:
| Doing it first is innovative
| dreamcompiler wrote:
| Musk said the 48v stuff was not innovative at all; they
| were only doing the latter things you pointed out.
| stephen_g wrote:
| I've been in the telco/digital communications space for
| years and all this stuff has run from 48V for decades. So
| basically plenty of electronic parts are already available
| with margins suited to 48V already since it's extremely
| common in other industries like the one I'm in.
|
| Automotive just tends to be a pretty slowly changing
| industry, but everything is ready for them to adopt 48V
| that other industries have been using for a long time,
| someone just needed to take the plunge I guess.
| carabiner wrote:
| Have you been able to look at the Tesla document? Do you
| think it'll meaningfully help the EE's at other automakers
| redesign their architectures?
| Tuna-Fish wrote:
| And to explain why this hadn't been done before/how we got
| here:
|
| Nothing in a car actually wants 12V DC. Most of the low
| voltage stuff will run better at 5V or below, while a lot of
| the higher voltage stuff would benefit from going as high as
| possible. 12V exists because DC-DC conversion used to be
| expensive, and you had to make a compromise about the voltage
| based on losses, wire thickness, and picking a low enough
| voltage that all the low-voltage stuff doesn't suffer too
| much.
|
| What's changed is that you can get a single-device DC-DC
| converter for really cheap these days. Cheap enough that you
| might as well put it in the light bulbs, and everywhere else
| that wants a low voltage.
| myself248 wrote:
| 12v exists because 6v was too low; wires were impractically
| thick for even the early accessories being added in the
| 1950s. The 6v-12v transition happened in 1955/56 for many
| cars. Some stuff like lightbulbs could be reused by putting
| two 6v bulbs in series in a 12v car, so it was a very cheap
| and relatively straightforward transition.
|
| If they'd just had some foresight and gone 48v in 1955, we
| would've saved 50 million tons of copper in the years
| since. It's no harder to make 48v motors or lightbulbs or
| relays or anything else (and in fact, the telephone network
| contains plenty of exactly those things, and has, in
| staggering numbers, for over a century), but the automotive
| industry isn't exactly known for being forward-thinking.
| 15155 wrote:
| > If they'd just had some foresight and gone 48v in 1955
|
| How would they have done this without cheaply-available
| high-speed switch-mode power supplies with low-DCR
| inductors/MOSFETs?
| myself248 wrote:
| Why would they need those?
|
| All the stuff that's natively 12 volts now could simply
| have been made natively 48 volts. You can make a 48-volt
| lightbulb as easily as a 12-volt lightbulb. You can make
| a 48-volt motor as easily as a 12-volt motor. Actually,
| motors for higher voltage tend to be smaller and lighter,
| which is why industry tends to go straight for 4160-VAC
| motors whenever 480VAC is inadequate.
|
| What applications cannot be made to work at 48? I'm not
| aware of any. As I said in the comment to which you're
| replying, the telegraph and later the telephone network
| had been running similar DC systems since the 1850s or so
| at various voltages depending on the length of the
| telegraph line, with the telephone network taking over
| and 48 volts firmly entrenched by the 1910s. There was a
| huge manufacturing base producing 48-volt equipment,
| including motors and generators, indicator lamps, and a
| mindboggling array of switches, relays, stepping
| selectors, and their ilk, and all that was before WWI.
|
| Furthermore, Charles Kettering who invented the
| automotive starter motor (and made it work at 6 volts),
| was around the same time making Delco-Light plants for
| rural electrification, which mostly ran at 32 volts DC.
| These supported a whole line of 32VDC appliances --
| lights, vacuum cleaners, kitchen gadgets, irons, motors
| that could be attached to other machines in the shop.
| There was also a less common 110VDC version of the system
| but I can't find any contemporary literature discussing
| the differences, although I'm sure they would've quickly
| discovered that the 32V system was pretty docile while
| the 110V encouraged extreme care around open contacts.
|
| As for why cars didn't use the higher voltages already in
| use and superior in many ways, my only guess is that a
| lead-acid battery with a high number of small cells
| must've been difficult or expensive to manufacture,
| compared to one with a small number of large cells. The
| Delco-Light plant used a large rack of 2-volt cells,
| whereas the starter motor used a single 3-cell packaged
| battery that fit easily under the hood. If they'd just
| figured out how to package more smaller cells
| together....
| 15155 wrote:
| > Why would they need those?
|
| To convert voltages to useful levels without suffering
| massive losses in efficiency.
|
| > What applications cannot be made to work at 48?
|
| Basically every logic-level transistor will not work at
| 48V. It's nice that these last-century analog devices
| could be made to operate at different voltages: present-
| day semiconductors are not so conveniently flexible.
|
| Simple physics dictates that required inductors to step
| between voltages increase in physical size (and weight,
| and material cost) as that voltage disparity increases.
| Capacitance required, etc. all increases with it.
| Efficiency plays into both of these as a triangle. Heat
| increases as this disparity increases. These properties
| are unacceptable for a myriad of use cases.
| robocat wrote:
| A 12-volt battery typically has six cells. A 48 Volt
| Lead-acid battery would have 24 cells - I'm not sure how
| that would change the constraints on charge balancing and
| starter-motor stress.
|
| I can say that the 24 Volt deisel vehicles I have used
| makes buying two batteries expensive.
| elihu wrote:
| I think another big part of it is that DC switches tend to
| get expensive above 12V. Cheap AC switches work fine at
| higher voltage, because the arc is self-extinguishing as it
| passes through zero twice per cycle, but DC doesn't do that
| so you can end up with an arc that doesn't extinguish
| itself, which, aside from not turning the thing off when
| you want to, burns out the electrical contacts.
| dreamcompiler wrote:
| Now we have MOSFETS and IGBTs that can switch DC without
| sparks. I suspect most DC switching in the Cybertruck is
| relayed through these. (Except the main contactor and
| pyro fuse of course.)
| myself248 wrote:
| And the contactor is usually switched with no current
| through it. The only time it would open under load is in
| an emergency, and presumably it only does that once.
|
| Which is to say, yeah, it's a non-issue for pretty much
| everything. Even in the 12v realm, new BCMs have so few
| relays anymore, almost everything's done with onboard
| FETs and software.
| elihu wrote:
| And given that this is a Tesla, it wouldn't really have
| had many mechanical switches in the first place. Maybe
| the turn indicator? Which could happily run at 5 volts or
| something and blink the lights via CAN bus messages.
| Kirby64 wrote:
| None, unless you count the physical buttons as
| 'mechanical switches'.
|
| The turn signals on a Tesla don't even make the
| 'clicking' noise if the Infotainment is rebooting,
| because it's literally just a noise piped through the
| infotainment.
| brandonagr2 wrote:
| Related to the weight of signal wires, Cybertruck also moved
| to using ethernet instead of traditional canbus, which
| significantly decreased the complexity of that harness
| sowbug wrote:
| Thanks for this detailed answer. The chassis is normally
| grounded. Has anyone tried sending a positive charge through
| part of it? Combined with a Powerline-style signaling system,
| some components wouldn't need wires at all.
|
| I already can think of several reasons why this wouldn't
| work, but I wonder whether there's a good idea in there
| somewhere.
| waterheater wrote:
| Compared to ICE vehicles, EVs are expensive and heavy
| (according to Slate, an F-150 Lightning weighs 35% more than
| its ICE sibling). Cost and weight reduction are both important
| factors for any EV maker to optimize.
|
| Why do you assume the 12V bus doesn't drive high-power stuff?
| Historically, every single electrical component in a car is
| powered at 12V. Everything. Your alternator outputs 12V to both
| power your electrical system and charge the 12V battery. Even
| the starter and ignition system (distributor or coil pack)
| transforms 12V into the high voltages needed for combustion.
|
| I'm not exactly sure why 48V corresponds to a decrease in
| "complexity." My guess is that power and data were sent over
| separate cables, whereas PoE does everything together. That's
| just a guess, however.
|
| Assuming the same power requirements, a 4x increase in voltage
| translates to a 4x decrease in current. Looking at [1], a
| component requiring 8AWG @ 12V can now use 18AWG @ 48V. That's
| a significant decrease in copper, resulting in cost and weight
| reductions. A higher voltage is almost always preferred, though
| the higher electric potential means you need better insulation
| and safety measures.
|
| Though there's a saying that it's current, not voltage, that
| kills, high voltage is widely known to be dangerous. For
| example, consider the US electrical grid, which is actually a
| 240V system, not 120V. Three wires come to your house from the
| transformer: -120V, 0V, and 120V. A normal outlet is connected
| to either -120V and 0V or 0V and 120V, and you can get a 240V
| outlet by connecting to -120V and 120V. This 120V-by-default
| setup is much safer than 240V every outlet, like in other parts
| of the world, and you can still get a higher voltage for high-
| power appliances (e.g. clothes dryer).
|
| [1] https://en.wikipedia.org/wiki/American_wire_gauge
| contingencies wrote:
| _Compared to ICE vehicles, EVs are expensive and heavy_
|
| Expensive maybe, IMHO not really, at least in China. Heavy ..
| this doesn't sound fair. Are you comparing a cherry-picked,
| heavy, full battery back EV with an empty tank ICE? Noting
| the EV has far more torque, and that the same tech is used in
| UAVs and in a ground vehicle you can arguably move the weight
| around (lower it) easier in an EV, this casual observer (not
| a car person) would expect superior mass distribution and
| lower overall weight (certainly vs torque).
|
| 500kg solar EV:
| https://www.unsw.edu.au/newsroom/news/2022/06/sunswift-7--
| dr... ... compare Toyota Corolla: 1314kg + 50kg fuel / Toyota
| Camry: 1360kg + 70kg fuel / Tesla Model 3: 1611kg / Toyota
| RAV4 average: 1634kg + 55kg fuel / Tesla Model S: 2107kg /
| Tesla Model X: 2458kg / Your cherry-picked example of an
| F-150 Lightning: 2948kg / Chevrolet Silverado 1500: 3311kg +
| 105kg fuel / way more heavier ICE cars follow...
|
| Another potential consideration is that the EV is far better
| placed to use recovered power from braking, so a small amount
| of additional mass will have less efficiency impact than in a
| comparable ICE.
| stonogo wrote:
| Vehicle weight also affects how much wear the roadways
| experience. I'm not sure "A Corolla weighs less than a
| truck" is relevant here, especially considering that the
| F-150 is the most popular vehicle in the US by sales
| number. Comparing things to the market leader is generally
| a useful metric.
| speedgoose wrote:
| Heavy trucks damage roads much more than cars. It depends
| on the weight but it's exponential. The weight difference
| between an EV and an ICE of the same category is not a
| big concern to have in terms of road damage.
|
| https://en.m.wikipedia.org/wiki/Fourth_power_law
| TaylorAlexander wrote:
| Why not use 48v? I have been designing my farming robot's
| electrical system and it all runs on nominally 45 volts. The
| switching power supply you need to downregulate that to 12, 5,
| or 3.3v (I have all three on one PCB) is tiny and cheap. [1]
|
| No matter what voltage or power level you need, higher voltage
| will allow for smaller/cheaper wires and connectors that are
| easier to route and assemble.
|
| [1] You can browse the Kicad PCB design directly in the browser
| with this handy web viewer. The power section is the top left:
| https://kicanvas.org/?github=https%3A%2F%2Fgithub.com%2FTwis...
| noncoml wrote:
| One example is Porsche PDCC. It needs 48V to work so you end up
| with a car that has both.
|
| Also I think all Mild Hybrids are 48V, so maybe theoretically
| you could get rid of the extra 12V battery there?
| codeulike wrote:
| As well as switching to 48V they are going to use Ethernet
| cables for most of it (PoE). So at the same time they get rid
| of the CAN bus wiring and have everything running on ethernet
| for communications and power, which means a LOT less wiring
| because with CAN bus every device needs its own wire but with
| Ethernet its much easier to have 'hubs' that channel
| communications and power on to other devices.
|
| https://twitter.com/cybrtrkguy/status/1731658374775771297?s=...
| adolph wrote:
| It is interesting to think about how an automaker like Tesla
| which is more vertically integrated and has less in the way of
| legacy parts/tools/processes can make this change more easily
| than the established players. From the article:
|
| _If you cannot convert all of a vehicle's systems to 48V
| architecture, the benefits of using such an architecture start to
| diminish pretty quickly . . . If an automaker decides to move to
| a 48V architecture, whatever car it builds must use 48V-ready
| accessories. But, suppliers aren't incentivized to build such
| accessories without sufficient demand._
| elp wrote:
| 48Vdc is supposedly the highest voltage that is still considered
| safe.
| (https://electronics.stackexchange.com/questions/267789/how-s...)
|
| It certainly sounds like a smart move on the copper savings
| alone.
| jauntywundrkind wrote:
| Extra low voltage is 50v ac or 100v dv.
| https://en.wikipedia.org/wiki/Extra-low_voltage
|
| For some reason people assume it's 48v DC or 50v dc. But it's
| double that. That said, I feel significantly more scared
| dealing with 100v DC than I do 48 or 24v.
| myself248 wrote:
| That's for IEC. Under OSHA it's 50 volts, AC or DC.
| sheepshear wrote:
| ELV is not a fundamental definition of "safe". The limits of
| what's safe depends on the application and your risk
| tolerance, and ELV is just a name for a couple of definitions
| out of many.
|
| Also, those numbers are for ripple-free DC, which you're not
| going to find in a car. They're cut roughly in half for
| ripple peaks.
| amluto wrote:
| I find 48V a lot less scary when cars are involved than 12V.
| Neither is particularly likely to electrocute me, but 48V
| comes with fuses that will trip at 1/4 the current, giving
| 1/16 the resistive heating if something shorts, which is a
| lot less likely to melt or ignite things. Also, the wires are
| much smaller :)
| thot_experiment wrote:
| > 1/4 the current, 1/16 the resistive heating
|
| Really underappreciated safety aspect. The currents
| required for your average doodad at 48V leave you with a
| MUCH lower chance of unscheduled welding.
|
| Remember folks, everything is a fuse if you put enough
| current through it, as a rule of thumb it's good to keep
| "enough" pretty low.
| dreamcompiler wrote:
| "The job of the transistors is to protect the delicate
| fuses."
|
| --old EE lore
| shermantanktop wrote:
| I used to work on vacuum tube power amps. 400v+ B+ with big
| caps is stressful to deal with. And doing it a lot can lead
| to complacency.
|
| We used to call getting shocked "getting a taste" - like
| getting a taste of ice cream, except it's more like a
| microsecond blackout.
| reportingsjr wrote:
| I have been shocked by 110V DC and let me tell you, it hurts.
| A lot. Would not recommend.
| SigmundA wrote:
| Remember a fully charged lithium battery with nominal 48v can
| be close to 60v just like 12v in your car is actually closer to
| 14v.
| wongarsu wrote:
| However there is a lot of leeway on the "48V is the highest
| safe voltage" statement too. 48V has a special place in
| regulations because of its use in telco, but 60V DC is still
| very safe.
| hinkley wrote:
| Doubling again to 96 is not safe, however. I'm not sure why
| they settled on powers of two. Something perhaps to do with
| noise filtration, and fewer new tricks to learn?
| myself248 wrote:
| It's convenient to build things in multiples and powers
| of 2 and 3. A nice two-tier or four-tier battery rack
| full of 2-volt cells just works out nicely.
| hinkley wrote:
| Smaller transformers with whole numbers, right? But why 4
| and not 3 or 6?
| eternityforest wrote:
| We seem to stick with 7-smooth numbers, and really extra
| prefer highly composite numbers
| (https://en.m.wikipedia.org/wiki/Highly_composite_number)
| for things we chose before the age of calculators.
|
| 3 and 6 were the standard voltages for consumer stuff
| back in the days of people needing to buy multiple packs
| of AA cells every year
| jjeaff wrote:
| Are we not all still buying multiple packs of AA
| batteries every year? Or maybe it's just those with kids.
| myself248 wrote:
| Oh I hope nobody's doing that, rechargeables have been so
| good for so long. I'm just now retiring some that I
| bought in the 2007-2011 timeframe which have started to
| fail, but my 2015 purchases are still going strong with
| hundreds and hundreds of charge cycles on 'em. I haven't
| used alkalines since the 80s.
| eternityforest wrote:
| I think it might mostly just be those with kids!
|
| And non techies. They always have a few disposable
| battery flashlights hanging around it seems like.
| eternityforest wrote:
| Aside from modern barrel jack supplies, none of it is
| actually powers of two, it's like, 13.8v lead acid or a
| little higher for lithium.
|
| I think we just stay close to the numbers we do, because
| we just really like multiples of 12 and numbers with lots
| of divisors. 24 hours in a day, 360 degrees, etc.
|
| Most numbers people really like a lot seem to be on the
| 7-smooth numbers(https://oeis.org/A002473) list and
| related/overlapping sets like highly composite numbers.
|
| Which I think is super cool, because it means you can
| choose one and there's a good chance someone else chose
| it too for something similar, unless they were using
| renard numbers or something instead.
| nippoo wrote:
| A lot of 48V infrastructure comes from the marine world -
| where 4 x 12V lead-acid batteries in series is common for
| this reason. So a lot of components already exist and can
| be made to work in the automotive sector with simple
| modifications. (In the marine world, it's much simpler to
| combine and split batteries in powers of 2 for cell
| balancing - you can take 4 x 12V batteries and charge
| them in parallel, discharge them in series)
| TaylorAlexander wrote:
| Sure but they can feed the system through a regulator if
| they'd like. Do we have any reason to believe they are
| tapping directly on to a pack for this part of the system?
| SigmundA wrote:
| Normally the battery is the regulator it serves to buffer
| inrush loads and absorb spikes.
| TaylorAlexander wrote:
| > Normally the battery is the regulator
|
| For a 12v system, of course. But on a modern 48v system
| who knows what they decided. Having a switching regulator
| with built in current limits might be helpful.
| myself248 wrote:
| For battery-powered systems the nominal voltage is used.
| Telephone "48 volts" is 55.2 volts in practice, only falling
| near 48 if there's a power failure and the office generators
| don't autostart in a timely fashion.
|
| That's never caused any regulatory problems for Ma Bell,
| despite OSHA saying 50v is the cutoff. And personally having
| spent roughly a decade of my career crawling all over such
| systems, 55.2 doesn't bother me one bit.
|
| Span-powered T1 at 130VDC, on the other hand.... that'll poke
| ya. That gets little plastic covers over all the terminals,
| but they have been known to fall off. So there is a
| meaningful threshold, and 55.2 is solidly below it.
|
| Which suggests to me that there's a good bit of leeway built
| into the standards, perhaps specifically so they don't have
| to wheedle about whether a battery system should be measured
| at its nominal voltage, its float voltage, its absorption
| voltage, its peak/equalization voltage, its....
| Tempest1981 wrote:
| > That's never caused any regulatory problems for Ma Bell,
| despite OSHA saying 50v is the cutoff
|
| I seem to recall getting a buzz when touching phone wires -
| while the line was ringing. I think I measured around 100
| VAC. Apparently that's "ok", safety-wise.
| myself248 wrote:
| Ringing is 90VAC, 20Hz, current limited. And it's only on
| for 2 seconds and then off for 4, so it's not like you're
| gonna grab on and be unable to let go.
|
| So, yeah, as a momentary thing it's not a hazard unless
| it tickles you off a ladder or whatever. Punchdowns and
| terminal blocks are normally mounted where they can be
| worked on from ground level so that's unlikely to be an
| issue.
| tzs wrote:
| > That's never caused any regulatory problems for Ma Bell,
| despite OSHA saying 50v is the cutoff.
|
| I'd be surprised if the wired phone system is not allowed
| to do a lot of things that would not be allowed under
| current codes and standards. By 1920 about 35% of US
| households had a phone. Upgrading all of that to keep up
| with evolving safety standards would probably have been way
| too expensive, and so I would expect that there was a lot
| of grandfathering.
| dfox wrote:
| > That's never caused any regulatory problems for Ma Bell
|
| Telco lines generally are not considered safe voltage. One
| thing is that ringing voltage is fairly squarely above the
| threshold and another thing is the whole outside plant
| thing (ground potential differences, lightning strikes...).
| reportingsjr wrote:
| 60V DC is the upper limit for circuits that untrained
| personnel can work on and be exposed to as listed in IEC
| 62368-1. This is the standard that most consumer goods and IT
| stuff use to validate and verify electrical safety. 60V isn't
| going to be hazardous to a person in basically any situation.
| eqvinox wrote:
| It's a bit of an arbitrary determination; 60V is the
| international common denominator on what various legal or civic
| (e.g. insurance) regulations consider safe;
| https://en.wikipedia.org/wiki/Extra-low_voltage#Separated_or...
|
| 48V is somewhat of a dinosaur from the days when you designed
| things with a 20% margin since that's what was cheaply
| attainable. Regular PoE is 54V these days (10% margin), and
| some more specific applications creep even closer to 60V. (I've
| seen 57V and 58.5V, which is of course 5% and 2.5%)
| dmix wrote:
| What's a commonly produced thing that's 48v? I don't know
| much about this subject. Is it most industrial type stuff or
| is there consumer tier products using it?
| somedudetbh wrote:
| ebikes, phantom power in audio equipment...
| stephen_g wrote:
| Basically the whole telco industry runs off 48V, and has
| for a very long time. You'd have a rectifier box that would
| take the AC and output 48V, and then everything would run
| from that.
|
| A lot of the satellite and wireless equipment I've worked
| on has inherited that and runs off 48 too.
| p1mrx wrote:
| 240W USB-C uses 48V, so that should eventually become
| common for stuff like gaming laptops.
| dharma1 wrote:
| Pro audio - most condenser microphones (except electret)
| run off 48v provided via the mixer/audio interface through
| XLR cables
| NotYourLawyer wrote:
| With wet hands, even 48v _hurts_.
| dade_ wrote:
| On my tongue, 9V hurts. There is pain, but no harm.
| rational_indian wrote:
| Could have gone higher. Worth it in copper savings alone. IIRC
| the cars use AC motors. It needs to go through inverters anyway
| so there is some flexibility in how high you can go.
|
| Edit: of course the motors are "AC" who would want a brush and
| commutator based motor in their car?
| bryanlarsen wrote:
| Most countries have safety rules that apply at 50V, so staying
| below that reduces regulatory costs significantly.
| rational_indian wrote:
| Good point.
| timerol wrote:
| The main motors of an EV are not powered off of the 48V system.
| EVs generally have 300-400 V main batteries, with discussion of
| 800 V on the table (someone may have already done it, I haven't
| been keeping track).
| elihu wrote:
| The terminology can get confusing. I many contexts, a
| "brushless DC motor" is actually a 3-phase AC motor.
|
| The idea is that you can think of the motor and motor
| controller (often called an inverter) together as a DC motor
| because the input to the motor controller is DC.
|
| Series-wound DC motors used to be fairly common for EV
| conversions, and they're still a reasonable choice if you want
| something that's very cheap and very powerful, and don't care
| about brush maintenance, efficiency, regen, or being able to
| reverse easily. (The White Zombie for instance uses a pair of
| SWDC motors.) Normal people just use AC motors these days.
| epx wrote:
| It would be great to have 48VDC in homes, for lightning, light
| appliances, etc. to centralize the whole power factor control in
| a single big power supply instead of doing it (poorly, or not at
| all) at every LED bulb.
| bryanlarsen wrote:
| It'll happen in RV's first, for obvious reasons. I imagine
| they'll use USB-C as the standard connector even though it's
| not the optimal form factor for this usage due to its ubiquity.
| POE would be a better choice.
| tootie wrote:
| Doesn't USB-C cap at 20V?
| ianburrell wrote:
| Latest USB-PD standard allows for 48V and 240W. It uses
| special EPR marked cables.
| candiddevmike wrote:
| Replace all power outlets with Ethernet and have everything run
| over 48V PoE and get network connectivity too
| bokohut wrote:
| While this sounds great in practice the reality will be far
| from ideal for the singular reason of security. The cyber
| issues are compounding at exponential rates as more and more
| devices that make things "easy" lack even the most basic
| security protocols and the production targets to generate
| revenue asap have zero to nil concern around protecting said
| devices from nefarious actors while in use. When the
| electrical and data transfer grid become one, as I believe it
| must for reasons of efficiency, we are certain to witness
| chaos and losses like never before. What you cannot see
| matters most! and in time many will pay the ultimate cost for
| someone else's 'easy'.
| vlovich123 wrote:
| More like basically every electronics product uses AC. It's
| a two sided market problem - there's no demand because
| there's no supply and no supply because there's no demand.
|
| The security aspects are solvable through various standards
| (eg we have LAN over power lines and coax already and they
| layer encryption on top to build the mesh while balancing
| UX). The security concerns may be the #1 concern for you
| but has nothing to do with market adoption.
| ianburrell wrote:
| PoE 802.3bt tops out at 71W. Not even enough to enough to run
| big USB-C adapter. Also, PoE is pretty lossy which defeats
| the whole purporse of using DC to save energy.
| bluGill wrote:
| You would need larger wires to account for the losses at a
| house scale. Since nothing runs are 48 volts you still have the
| bad power supply in every LED bulb.
| dreamcompiler wrote:
| 12 gauge wire would work fine for 48v lighting loads;
| probably 14 gauge too for many of them. Small DC constant-
| current sources are commodity items now and they're very
| efficient.
| bluGill wrote:
| 12 gauge is more expensive, and harder to work with.
| dreamcompiler wrote:
| And it's already in a lot of houses, which was my point.
| jnsaff2 wrote:
| The Dutch have some homes that are DC. Here's even a paper
| discussing this[0]. There is also a presentation that mentions
| DC homes from page 18[1].
|
| [0] - https://www.irbnet.de/daten/iconda/CIB2595.pdf [1] -
| https://fhi.nl/app/uploads/sites/38/2018/06/10.00-DC-Power-e...
| ianburrell wrote:
| The DC power for LED varies based on the bulb and most are less
| than 48V. Which means you end up with DC-DC converter in each
| one. DC-DC is slightly more efficient than DC-AC but not enough
| to make worth converting.
|
| The same is true of electronics, you are replacing AC-DC
| charger with DC-DC charger.
|
| The other big problem is that lots of appliances require more
| power than feasible with 48V. People are fine with the low-
| power DC right up until they need to plug in a space heater.
| Are you going to have two kinds of outlets everywhere? Or
| incrementally upgrade each circuit? Or are going to upgrade the
| wiring with super thick cable that can handle the current?
| teruakohatu wrote:
| > Are you going to have two kinds of outlets everywhere?
|
| People already do, with usb sockets sitting next to mains
| sockets.
|
| Of course if you standardise on usb-c you are still doing dc
| to dc (and all sorts of extra things) so not much point as
| you pointed out.
| londons_explore wrote:
| Am I right in saying this _wasn 't_ shared with the public or
| other (Chinese) OEM's...
|
| Doesn't that raise collusion/anti competitive concerns? Or is
| Elon relying on the fact no prosecutor will take a case about
| disadvantaging china?
| KaiserPro wrote:
| "shared" in the sense that everyone else was doing it already.
| In the same way that he's shared the hyperloop, which he got
| from a 1980s osbourne book of transport.
| panick21_ wrote:
| I think the more important change that Tesla made is the change
| in the databus. Much higher performance ethernet. They changed
| the whole architecture of the car where there are now very few
| point to point connection, and its all essentially routed with a
| few major modules in each part of the car.
|
| If you look at current cars there are sometimes huge cable
| bundles, lots of individual cables for everything. Its a
| nightmare to build up and very hard to install.
|
| I think in their next generation assembly they will have these
| connection points be fixed and then just plug different sub
| assembly together at predetermined points. No more huge cable
| harness installed on completed bodies.
| KaiserPro wrote:
| > Much higher performance ethernet.
|
| Depends what performance you are after. Ethernet isn't rated
| for safety critical stuff. It doesn't provide mechanisms for
| packet loss detection, and in most cases is pretty shit at flow
| control.
|
| Ethernet is also shit for small sensors/actuators. There are
| lots of low bandwidth devices that need power and comms,
| ethernet isn't designed for that. having to route 2 pairs of
| cables to everything in a star pattern is really impractical.
|
| Its probably ok for linking different zones, of non critical
| stuff. But running PoE? for all but specialist things, that
| sounds frankly stupid.
| sephamorr wrote:
| There has been a lot of work developing standards for
| reliable ethernet for industrial and automotive applications,
| resolving most of the issues you mention which apply to
| 100/1000Base-T. Tesla isn't using your garden variety
| ethernet or abominations like ethercat.
|
| 100/1000Base-T1 is intended to be used with PoDL (802.3bg/cu)
| and TSN (various 802.1Q)to result in reliable links with
| guaranteed latency and bandwidth properties. PHY power is a
| few hundred mw though, and star topologies are limiting to
| replace CAN/LIN nodes, that's what 10Base-T1S is for though
| (cheaper, bussed, lower power).
| 7e wrote:
| Mild hybrids have been using 48V for a long time. There isn't
| much new here except that Tesla decided to do every component.
| That's going to cause quality problems with parts if they remain
| a tech. island in the industry, so trying to get everyone else on
| board makes sense.
| panick21_ wrote:
| Doing it for everything is the whole point, it changes the
| architecture of the car. Yes individual components but those
| cars had like 1% if connected devices at that voltage and were
| otherwise exactly the same.
|
| For Tesla ist a replacment of something else, for previous
| vehicle was it was something additional for a specialized use
| case.
| yinser wrote:
| I liked the interview with auto engineer Sandy Munro discussing
| the change https://youtu.be/ADwGGEj8sqQ?si=qp6akvy1yyWPTYNe
|
| - moving the voltage up means you can drop current
|
| - increase the data rate by using ethernet and PoE
|
| - using ethernet and PoE means you don't have to run one off
| wires to each device, they can share a bus which results in half
| the copper being used in a lower voltage car
|
| - moving the voltage up also means reduced heat produced
| TheLoafOfBread wrote:
| > using ethernet and PoE means you don't have to run one off
| wires to each device, they can share a bus which results in
| half the copper being used in a lower voltage car
|
| You mean like CAN bus is being used since 1990s? I think that
| Mr Munro little bit fell asleep and missed whole CAN bus and
| FlexRay evolution in cars.
| thepasswordis wrote:
| CAN bus is still really slow (1Mbps, so bus contention is a
| problem). Sensors, cameras, AV stuff, etc. can't all live on
| the CAN bus. Cars are not the same things they were in the
| 90s.
| sbierwagen wrote:
| >cameras
|
| Yes. Post 2021 teslas have nine cameras scattered all over
| the body. For AV, Tesla would like to get much higher
| resolution and frame rates out of them.
| TheLoafOfBread wrote:
| CAN bus is multi-master access with automatic arbitration
| between nodes. Something what Ethernet is completely
| incapable of and that's the reason why CAN bus is here to
| stay for a long time.
|
| Ethernet needs active switches isolating each branch of the
| star network from each other. Because Ethernet working in
| bus mode is absolute joke, slower than CAN bus if you add
| enough nodes to such network. But when you need to drag all
| sensors and ECUs to a center of a star where is switch,
| where is the saving on cables?
|
| Even worse, there is no guarantee that node on such network
| will be able to deliver message to other node, thanks to
| CSMA/CD which says Random disconnection if collision. Well
| guess what? Your wheel just locked during braking and we
| need to tell that to ABS/ESP unit. When using CAN you can
| rectify it by using low CAN ID and thus increasing priority
| in arbitration. When using Ethernet, you are only praying
| to RNG Jesus.
| KaiserPro wrote:
| > using ethernet and PoE means you don't have to run one off
| wires to each device, they can share a bus which results in
| half the copper being used in a lower voltage car
|
| Ethernet isn't a bus, its point to point. PoE over cat5/6 uses
| 4 pairs of UTP.
|
| so it might be used to join aggregate things together, but it
| won't be a bus.
|
| Yes, you can increase the datarate, but ethernet is
| fundamentally unreliable. So you'll need to either strictly
| manage the bandwidth requirements of attached devices, or put
| in flow control(expensive) or use the weird "reliable" Ethernet
| they made for fibre channel replacment ($lol and you need to
| pay to make it automotive rated)
|
| 48v is logical, and a lot of other people are doing it.
|
| PoE is probably stupid
|
| Ethernet makes kinda sense, but firewire would probably be
| better, its a bus and rated for life critical use.
| TheLoafOfBread wrote:
| Ethernet can be used as a bus (see CSMA/CD), but if there are
| more than 2 nodes, performance of whole bus will go to
| complete shit and there is no guarantee that an ECU will
| transmit a single packet during its run, because that CD has
| no automatic arbitration, it is just random disconnection and
| try again. Not good for critical things like ABS. That's also
| whole reason why FlexRay was spawned, because even that FR is
| inflexible abomination of a protocol it actually guarantees
| that every ECU on the network will get a time window to
| transmit its own data.
| KaiserPro wrote:
| > CSMA/CD
|
| Lol I'd forgotten about base-T.
| andrewf wrote:
| I think that's what 10BASE-T1S (standardized in 2019) is
| for. It has a non-CSMA/CD arbitration scheme. https://www.e
| lectronicspecifier.com/industries/industrial/an...
| TheLoafOfBread wrote:
| So... you need new PHYs and new Ethernet controllers to
| use T1S?
| andrewf wrote:
| A lot of the Googleable information seems to be from chip
| vendors who want to sell those things :) Yeah it's
| intended for new designs. Fewer wires than the original
| 10mbps ethernet.
| eglretgj wrote:
| I work for another EV manufacturer. Good God I would love to
| switch from CAN to ethernet. We already have way too many CAN
| buses and we're considering adding more. But it will take
| decades for our suppliers to even consider the switch. We just
| paid Bosch $15M for an upgrade to our brakes, they promised the
| change in six months, it took them two years and quite a few
| additional millions of dollars, and it's filled with bugs. We
| can't even run the new brake firmware on public roads it has so
| many bugs. And we'll have to pay them millions more and wait
| months or years more for them to fix their own mistakes. This
| is why Tesla does almost everything in house. I wish my company
| had the resources to.
| TheLoafOfBread wrote:
| Well, then you should maybe ask why do you need such
| complexity, when cars 5-10 years did not needed to do exactly
| same task - taking a person from point A to point B.
| poisonborz wrote:
| But doesn't that mean a single point of failure, a single
| network problem stopping the whole car? I guess there must be a
| historic reason for mostly direct CAN connections.
| pedrocr wrote:
| Golf carts have used mainly 48V for traction for a long time. And
| there are now great options for 48V LFP batteries for them. So
| far that usually means also running a 12V converter to power
| accessories. If the automotive world finally gets their act
| together on 48V this will be great for all kinds of DIY uses. The
| batteries and chargers are already here. There are a bunch of off
| grid and mobility applications that should be made simpler by
| this. Hopefully the automotive supply chain moves meaningfully
| around this.
| MisterTea wrote:
| I've been waiting for higher automotive voltage for a long time.
| Way back I wished for 48V as it's double the 24V standard used in
| European and off highway trucks as well as industrial automation
| and -48V is used in telecom. Wires can now carry 4x power. But
| from memory there was a 50V safe limit that would complicate
| things as the 48V charging voltage exceeds 50V as does the
| nominal cell voltage. So instead the industry selected 36V and
| planned to migrate but it never happened. The reason being LED
| lighting and small more efficient electronics reduced the need
| for higher voltages.
|
| With EV's there's no reason to keep 12 V.
| jnsaff2 wrote:
| The "expert" in the article got it wrong. The relationship
| between the voltage and the losses in the wires is not
| proportional. They are squared. Going from 12V to 48V is not a
| saving of 4x rather 16x.
|
| For some applications you could also consider Power over Ethernet
| in the car, get both shielded comms and power. Or can and power
| over twisted pair.
| contingencies wrote:
| The great thing about PoE standards is there's so many to
| choose from.
| https://en.wikipedia.org/wiki/Power_over_Ethernet#Standards_...
|
| Honestly, ethernet introduces a degree of non-determinism with
| respect to time in the link layer, plus increased bringup
| times, a potentially more costly core switching fabric, and the
| need for critical revision of latency assumptions on any
| potentially safety-related control concerns. Also, max current
| is not high. I would wager these are the reasons it won't be
| rushing to an EV near you... it's basically only suitable for a
| subset of uses, and heterogeneous infrastructure costs more in
| design, installation and maintenance cost than it nominally
| saves in production volume standards alignment and HR
| familiarity. (Source: Mechatronic systems design for the last
| ~8 years, IANAEE)
| jnsaff2 wrote:
| Sure. It's also not like there are many ready made devices
| that are already available for PoE that could be useful in
| automotive industry.
|
| I guess my main thought was that going to 48V and in the
| world of low power LED lights and such, combining power and
| comms into same wires/cables is something that might be
| appealing.
| contingencies wrote:
| Historically and increasingly, automotive grade electronics
| are a separate genre to general electronics for reasons of
| safety.
| bgnn wrote:
| It's less of a safety but more of a production and
| environmental constraints issue. Cat5 cables are too
| heavy for cars. Their connectors aren't made for
| vibration. They have a lot of emissions which is a
| problem for the mission critical parts (Ethernet Phy
| often isn't mission critical). They are expensive, which
| is actually the biggest reason they aren't good for
| automotive.
|
| Automotive reliability is only an issue for your ABS
| sensor, airbag sensor etc. but these are a minority
| compared to what's in modern cars these days. Real driver
| is cost, compactness (cost) and harsh environment
| (temperature and vobrations) and EM emissions. It mainly
| adds to qualification time, but actual semiconductor
| design cycle isn't that long. That being said, data
| center stuff is also notoriously slow to qual.
| bgnn wrote:
| Automotive ethernet over copper physical layer is
| completely different than commercial/data center ethernet.
| It is defined in 802.3ch for multi gigabit (2.5, 5 and 10
| Gbps). It uses single shielded twisted pair cables up to
| 15m long. Cables and connectors are automotive grade.
|
| The power over data line (PoDL, automotive Ethernet
| equivalent of PoE) is defined by a separate IEEE protocol
| and its critical specifications like EM emissions tests,
| ESD tests etc are supplemented by documents created by a
| consortium of car, electrinics, comnector, cablr and
| semiconductor producors called OPEN Alliance:
| https://opensig.org/ . There are parts available for PoDL.
| The voltage levels from 6V to 60V with 6V increments are
| supported.
|
| Source: I design both data center and automotive Ethernet
| chips.
| rfdonnelly wrote:
| Regarding deterministic latency, the Time-Sensitive
| Networking (TSN) [1] set of IEEE standards address this. The
| IEEE P802.1DG project [2] in particular defines a TSN profile
| for automotive.
|
| [1] https://en.wikipedia.org/wiki/Time-Sensitive_Networking
| [2] https://1.ieee802.org/tsn/802-1dg/
| eqvinox wrote:
| > The great thing about PoE standards is there's so many to
| choose from.
|
| There is nothing to choose there. They're supersets of each
| other with increasing power budget, each including the
| previous revision as lower power classes.
|
| (and PoDL is not PoE; PoDL is for automotive ethernet, which
| has nothing to do with the RJ45 you see everywhere on
| consumer/business IT. You never choose between PoDL and PoE,
| the choice is made when you decided between Xbase-T vs.
| Xbase-T1.)
|
| > ethernet introduces a degree of non-determinism with
| respect to time in the link layer
|
| That's what TSN is for, cf. sibling comment.
|
| > plus increased bringup times
|
| That's generally an IP problem, not Ethernet.
|
| > a potentially more costly core switching fabric
|
| I guess it depends on your application; a TSN-capable 8-port
| automotive ethernet switch is $10:
| https://www.digikey.com/en/products/detail/microchip-
| technol... (non-TSN non-automotive is cheaper...)
|
| > heterogeneous infrastructure costs
|
| Automotive ethernet is supposed to replace CAN _and_ the
| various heterogeneous higher-speed interfaces that were added
| to deal with higher bandwidth requirements with a homogeneous
| ethernet world :)
|
| (Source: I work on some software remotely related to some of
| this shit. Which does mean I'm biased since I don't know
| whether it will in fact proliferate, I just make it work ;)
| dezgeg wrote:
| Ethernet is already used to transmit radio signal over fiber
| which requires extremely tight variation in latency (probably
| more strict than automotive).
| numpad0 wrote:
| Automotive Ethernet is not 8P8C...that's not how they do it at
| all
| Moto7451 wrote:
| Some cars even use optical networking between the front and
| rear of the car. I think a bit of that has gone away now that
| you don't need a DVD full of map data in its own module in
| the trunk.
| eqvinox wrote:
| You don't need it for the DVD anymore, now it's the
| zillions of cameras instead. The IEEE recently standardized
| automotive (= single pair) multi-gigabit ethernet
| (2.5/5/10GE) in 802.3ch...
| amelius wrote:
| If you go to a higher voltage, you will typically use smaller
| wires.
| hinkley wrote:
| Tesla didn't invent 48 volts either. The EV and hybrid electric
| world were talking about 48 volts when Musk still worked at
| PayPal, if not earlier.
|
| One of the examples pulled out at that time was that you could
| shave a couple pounds of copper off the alternator by running
| it at 4x the voltage. Much thinner wires.
| jsight wrote:
| Tesla's greatest innovation is simply leadership. Everyone
| knew castings were the way to go, but noone did it. Now
| people like Volvo are doing them, and I expect a lot of
| others to do it as well.
|
| Everyone knew that 48V would be a big benefit, but noone did
| it.
|
| TBH, in a few years, we may be saying similar things about
| drive-by-wire without a mechanical backup. But it is too
| early to say definitively.
| p_l wrote:
| What everyone was waiting for was for Italians to make the
| huge casting press so that castings could be done in mass
| production at automaker margins.
| jsight wrote:
| Despite Tesla's boastings, large casting machines have
| existed before. Automotive use is the new part.
| p_l wrote:
| Essentially it was question casting of this size being
| automated at car maker scale. Bigger castings were
| integrated before on assembly lines, but at higher costs
| and complexity before Italians made the large mostly
| automated caster that Tesla called GigaPress (iirc) -
| it's essentially COTS factory equipment.
| CharlesW wrote:
| > _Everyone knew castings were the way to go..._
|
| The jury's still out on whether gigacasting is courageous,
| or just moves costs from production (which will not be
| passed to consumers) to repairs (which will).
|
| > _Everyone knew that 48V would be a big benefit, but noone
| did it._
|
| Audi did in 2016 with the SQ7 TDI, no?
| bagels wrote:
| Car A costs $5k less to manufacture than car B because it
| uses castings. Car A would be wiser to build because you
| can get better margins, or lower prices. It'll take a lot
| longer for buyers to catch on to the fact that the car
| costs a lot more to repair.
| biaachmonkie wrote:
| The question is really if the castings result in more
| cars being written off as total loss. Any collision
| severe enough to damage them would likely be severe
| enough to also total out a car without them as well.
| jsight wrote:
| TBH, the repairability concerns seem to be overstated so
| far. There are still conventional crash structures in
| front of and behind them. It takes a lot to damage the
| casting beyond repair.
|
| You are right, though. The jury is still out in that they
| haven't really been used in the real world for long.
|
| > Audi did in 2016 with the SQ7 TDI, no?
|
| I didn't know about that one, but it was still a dual
| architecture. Going full 48V is a bit different, assuming
| Tesla really did that.
| hinkley wrote:
| Clearly no MGB fans at Tesla. The unibody is cool unless
| you live somewhere with snow, and then rust doesn't just
| make your car ugly, it makes it unsafe. And expensive to
| fix.
|
| Which is why I was always more of a Triumph fan.
| Turskarama wrote:
| The mechanical backup for a drive-by-wire system is
| different to all those other things in that it's a critical
| safety issue. If _anything at all_ happens to the
| electronics while driving then it's important that you can
| stop the vehicle safely. That mandates manual brakes and
| steering, even if they're barely effective at all without
| power it's a lot better than nothing.
| dreamcompiler wrote:
| The cybertruck has two separate steering motors for
| redundancy. Passenger jets have been doing "x-by-wire"
| for decades. Properly engineered it's as reliable as
| mechanical linkage.
| Turskarama wrote:
| Two motors is great and all, but that only provides motor
| redundancy and won't help if something happens to the
| electrical system.
|
| Planes are fly by wire but that's because they literally
| have to be, no amount of gym time will let you move the
| rudder on a 737 by hand.
| masklinn wrote:
| The 737 is not fly by wire.
| Turskarama wrote:
| Ok fair enough, it is hydraulic assisted instead but for
| the point I'm trying to make it's essentially the same
| thing in so far as it requires power.
| jsight wrote:
| I tend to agree, TBH. People bring up fly-by-wire, but
| even that is simpler. AFAIK, those systems aren't
| variable ratio the way CT is. CT literally will have
| different steering ratios depending on the speed, so one
| steering wheel angle will have different effects on the
| actual steering angle depending upon the speed.
|
| How will that work in the real world? Could there be
| bugs? Will people get used to it or will it lead to
| mistakes?
|
| I'm looking forward to getting a chance to try it, TBH.
| hinkley wrote:
| I hear it's kind of a pain in the ass to do a front end
| alignment on the drive by wire systems.
| phkahler wrote:
| >> Tesla's greatest innovation is simply leadership.
|
| Totally correct. We were making 48v power steering systems
| 20 years ago for OEM development projects. They simply
| don't have the will/commitment/leadership to bring change
| like that to market.
|
| Elon sets a direction and people go that way. I can imagine
| someone at GM listing all the obstacles as a reason they
| can't change, and Elon looking at them and saying "no,
| you're the obstacle" or something like that.
| DennisP wrote:
| Sure, people have been _talking about_ 48 volts for the past
| 30 years. Somehow most automakers didn 't actually manage to
| do it though.
|
| Sandy Munro just did an interview with Musk, who said they
| hadn't done anything revolutionary, they just built the car
| up to general 21st century standards.
| dreamcompiler wrote:
| https://youtube.com/watch?v=ky1Z2klPalw
| grecy wrote:
| > _The EV and hybrid electric world were talking about 48
| volts when Musk still worked at PayPal, if not earlier._
|
| You are confounding the two electrical systems in an EV or
| hybrid (or mild hybrid).
|
| One is used to drive the wheels - these are _very_ commonly
| 48V in a mild hybrid and something like 200V or 400V or 800V
| in an EV. This is _only_ used to power the wheels - nothing
| else.
|
| The other electrical system is used to power literally
| everything else. The infotainment system, heated seats, power
| windows, lights, powered seats, electric power steering,
| electric assist brakes, etc. This has _always_ been 12V in
| every car ever ^ (ICE /hybrid/EV) (including every Tesla).
|
| The Cybertruck is the first vehicle ever to move the 12V
| system to a 48V system.
|
| ^ Before about 1955 it was 6v. The move to 12v then was the
| last time it has changed.
| hinkley wrote:
| I'm talking about the same thing. Pumps and compressors and
| electronics systems.
| grecy wrote:
| You're talking about some of the things that would be on
| the accessory belt (serpentine belt) on an ICE, that need
| to keep spinning even when the ICE is off (power
| steering, A/C, etc.). That is a slightly more fancy
| engine start/stop.
|
| You are not talking about high current devices like
| heated and cooled seats, defrosters, infotainment and
| audio amps, power windows, power seats, lights, etc. etc.
| tzs wrote:
| Hold on a second...4x the voltage means you only need 1/4th the
| current. The power loss in the wire is current^2 x the wire's
| resistance, so 1/4th the current does indeed mean 1/16th the
| losses.
|
| But 1/4th the current means you can use a higher gauge wire.
| Looking at a table of wire gauge current capacities it looks
| like if your maximum current is 1/4th you can switch to wire
| with 1/4th the cross section. And resistance is inversely
| proportional to cross section, so 1/4th the cross section means
| 4x the resistance.
|
| Doesn't that then bring the savings down from the 16x you would
| get if you just upped the voltage down to 4x?
| satiric wrote:
| Yes, typically the savings would be in the weight and
| physical size of the wiring harness (as well as possibly
| allowing for tighter bend radii). You'd design for a max
| amount of heat generated by the wiring harness, or possibly a
| max voltage drop if that's a constraint. You don't need to do
| heat dissipation calculations yourself, there are standards
| like SAE AS50881 that do the heavy lifting for you.
|
| Edit: Smaller wire is also cheaper of course. That's probably
| a pretty significant upside when talking about a mass-
| produced vehicle.
| myself248 wrote:
| There's also a minimum wire size, based on physical
| durability requirements. A significant number of wires in the
| harness already carry no appreciable current and are merely
| signaling wires, but they can't be infinitely thin.
|
| Getting most of the power wires down into the range of signal
| wires is a huge benefit, because it means they can use common
| terminals and smaller connectors, but that's where it stops.
| aidenn0 wrote:
| For very low current wires, I've seen non-metalic (nylon?)
| strands woven in with the copper for mechanical strength.
| dreamcompiler wrote:
| Good point and you're not wrong. One mitigating factor is
| that resistance isn't constant: In copper it increases with
| temperature, and I^2R causes temperature to go up, which
| causes resistance to go up, and you get something of a
| positive feedback loop. Temperature rise is one of the main
| reasons why standard wire gauges are specified the way they
| are.
|
| If you use 4x higher voltage, the temperature rise is much
| less significant (16x less significant to be precise) so it
| becomes more or less a non-issue and you can treat resistance
| as a constant.
| jrockway wrote:
| > Or can and power over twisted pair.
|
| I was reading an anti-Musk subreddit over on Reddit and I think
| the cybertruck is doing this? They were mad that the cybertruck
| uses 48V and Ethernet cables, but to me, that seems perfect for
| CAN and power. We already use 48V (or similar) for PoE, and CAN
| needs a twisted pair... so why not buy that off the shelf
| instead of using a custom wiring harness?
|
| I don't think the cybertruck is a particularly attractive
| vehicle, but I also don't think they're crazy for trying that.
| You can do 10Gbps over a cat-6 cable and it works great. So I'd
| expect that you can easily do CAN.
| dreamcompiler wrote:
| Musk has publicly stated that CAN is too slow for modern
| cars, which is why they chose ethernet for the Cybertruck.
|
| https://youtube.com/watch?v=ky1Z2klPalw
| hef19898 wrote:
| CAN buses run into bandwidth issues at some point. Just
| remove all the OTA, car-as-a-service and de-facto
| surveillance crap, and one should be able to get away with
| CAN buses.
|
| Nothing wrong with ethernet, but listening to Musks
| statements, especially in fields I have some not even deep
| knowledge, alwqys like listening to a very confident, but
| otherwise clueless, 1st semester student selling you
| semester 2 basics as the latest and hottest shit under the
| sun nobody else even considered possible so far...
| noughtme wrote:
| Didn't read the article, but Musk mentioned in an interview
| yesterday they are specifically not using CAN and are using
| Ethernet. He didn't explicitly say, but it seems likely they
| are using PoE, saving a lot of wiring as you can daisy chain
| a higher bandwidth connection and you don't need separate
| power cables.
|
| https://youtube.com/watch?v=ky1Z2klPalw
| Geee wrote:
| Yeah, Elon talked about this in his latest interview with
| Munro. It seems that they just use Ethernet rather than CAN
| bus.[0]
|
| [0] https://youtu.be/ky1Z2klPalw?t=791
| grepfru_it wrote:
| I actually run Poe in my car to power a mini pc in the trunk. I
| guess I'm ahead of the game :)
| simplypeter wrote:
| The thing is, unless the whole industry moves together to 48V,
| the cost of this change for a single OEM+Tier1 would be too big.
| MetaWhirledPeas wrote:
| In cases where they're using a proprietary 48v part I wonder if
| Tesla would consider becoming a parts supplier to other
| manufacturers?
| SilverBirch wrote:
| This is basically the crux of the matter. Traditional
| automakers are a complex supply chain that standardises and
| goes to extra-ordinary lengths to reduce costs. Tesla build a
| tonne of their own stuff and aren't as price sensitive. The
| question is "Why don't we just redesign all this stuff" and the
| answer is "We're Ford, we make tiny margins and we can't afford
| to redesign our entire car every year and even if we could we
| get half our components from Bosch anyway". Not to mention the
| difficulty in convincing FuSa people your arbitrary ethernet
| network is safe.
| rasz wrote:
| You mean like EV cars? :)
| jmrm wrote:
| >48V architecture also potentially improves overall electrical
| efficiency for reasons that I am not sufficiently qualified to
| explain beyond a kindergarten level
|
| This is double bad in a green energy and EV website: On one hand,
| they admit they don't now why that happens, but on the other
| hand, they also didn't research just a bit more on that, and
| that's bad journalism.
|
| Most of the comment threads in this HN post are a lot more
| informative than the article
| CamperBob2 wrote:
| Also, "But don't you dare threaten to replace me with an LLM.
| Journalism is a sacred cornerstone of democracy and
| intellectual life!"
| wnevets wrote:
| I don't know if I would call a self proclaimed content
| marketer a Journalist.
| ipaddr wrote:
| He said "Journalism". A non-journalist can produce material
| that can be considered journalism. A student can teach. A
| homemaker can even write working code.
|
| The labels we give to others to divide us
| wnevets wrote:
| > The labels we give to others to divide us
|
| They gave the label to themselves
| eternityforest wrote:
| I always wondered why there's not some kind of nonprofit
| volunteer journalism organization you can get involved
| with.
|
| It doesn't appear to be something anyone tries to get
| normal citizens into, despite the fact that we constantly
| try to convince people to learn other stuff with much
| less individual scale value, sometimes even somewhat
| crazy stuff like home chemistry experiments with lead
| salts.
|
| I always thought that's what I'd want to do with my life
| if I wasn't coding, and maybe I'd be happier if I had
| gone to college and studied journalism...
| commoner wrote:
| Have you tried writing for Wikinews?
|
| https://en.wikinews.org/wiki/Main_Page
|
| Unlike Wikipedia, Wikinews allows and encourages original
| reporting. You don't need a journalism degree to
| contribute an article.
| niemandhier wrote:
| Because it would probably be overrun by the very
| opinionated.
|
| This happens frequently with new political parties:
| Someone starts an organisation, it get some amount of
| traction. Suddenly a lot of new people join and turn the
| whole thing into a tool to spread their views.
|
| AFD in Germany started like this, it almost happens to
| The Pirate Party, one can argue that Green Parties tend
| to suffer from this phenomenon.
| arcticbull wrote:
| > The labels we give to others to divide us
|
| Labels are an optimisation, an imperfect shortcut. They
| are a way we represent ourselves to others. If you don't
| tell me you're an engineer, I have to ask a ton of
| questions to assess your area of competence and skill. If
| you tell me you're an engineer I can save minutes or
| hours by putting you in a rough box. If that box is
| unnecessarily constraining it'll become clear as we spend
| more time together.
| ipaddr wrote:
| When race, gender, sexuality are involved we agree that
| labeling to save time isn't something accepted. For all
| of the reasons why shouldn't label those groups applies
| other labeling.
| arcticbull wrote:
| Most agree that we shouldn't actively do it, but we
| definitely do it consciously and subconsciously. It's a
| very human trait, even if we don't like it. The brain
| just doesn't have the capacity to evaluate everyone from
| scratch every time, so it takes shortcuts, and 'accepts'
| people based on the way they present themselves. The
| kinds of clothes they wear, shoes they're wearing, and
| accreditation from mutually trusted institutions. I agree
| the shortcuts that cause harm should be curbed to the
| best of our abilities but we can at best notice it and
| correct after the fact - but it'll still happen.
| CamperBob2 wrote:
| (Shrug) He called himself one, although admittedly in a
| former role before moving to Electrek.
|
| The point stands. People who DGAF about their jobs are
| going to lose them, and that's not a bad thing.
| jondwillis wrote:
| In before the ex-content marketers are breaking into your
| house to steal things to fence on Amazon...
| dududhxhd wrote:
| Nonsense. It's a bit of self deprecating humor and gives
| readers enough information to follow along.
| rasz wrote:
| "Before joining Electrek, David was a mobile technology
| journalist for over a decade at Android Police, where he
| started as a writer and went on to serve as Editor-in-Chief.
| He later accepted a side quest in the world of startup
| marketing, heading up content and product marketing
| initiatives at two SaaS companies."
| vampiresdoexist wrote:
| I mean... it's definitely more of a blog than a strict
| journalism outlet in the vein of say Bloomberg and whoever is
| on the EV beat.
|
| The writer isn't publishing false information, and it's good
| that the comments are able to add more value! It's a casual
| style that has humility and a touch of personality. That's ok!
| NelsonMinar wrote:
| I wish the article had more info too. But I appreciate the
| author acknowledging the limit of their work and not trying to
| bullshit or skip over it.
|
| I read Electrek daily and find it very useful. They cover a
| broad range of topic with more insight and voice than the usual
| crappy blogs that just rewrite press releases or someone else's
| articles. I particularly like the articles (like this one) that
| have "Electrek's Take". The Weird Alibaba EV articles are good
| fun too: https://electrek.co/guides/alibaba/
| 1970-01-01 wrote:
| >potentially improves overall electrical efficiency
|
| Looks like he understood it the entire time :)
| accrual wrote:
| I wasn't sure, so I asked:
|
| > Higher voltage systems experience lower power losses over
| the same distance compared to lower voltage systems. This is
| due to the fact that power loss in a conductor is
| proportional to the square of the current. By using higher
| voltage, you can transmit the same amount of power with less
| current, reducing resistive losses in the wires.
| jdewerd wrote:
| 12 Volts is 12 Watts per Amp.
|
| 48 Volts is 48 Watts per Amp.
| 1970-01-01 wrote:
| Woosh. There's potentially a joke in there if you read it
| again while understanding the applicable equation for
| electrical power.
|
| (V^2)/R
| accrual wrote:
| Woosh indeed, haha. I'm no EE but it sounded plausible.
| Maybe I'll get the joke if I do some actual reading. :)
| bsza wrote:
| > they admit they don't now why that happens
|
| No, they said "not sufficiently qualified to explain". Which is
| not the same as not knowing, given that the same phenomenon can
| be explained on a lot of different levels depending on when you
| get tired of asking "why?" - see this video of Richard Feynman
| "explaining" magnets: https://m.youtube.com/watch?v=MO0r930Sn_8
| kelnos wrote:
| To me that difference doesn't really matter. At the very
| least they should have educated themselves, and then provided
| links to resources to allow people to understand if they
| didn't feel comfortable explaining it directly.
| LeoPanthera wrote:
| This is not too surprising for Electrek, which is run by
| Tesla/Elon fanboys and mostly got popular by accident during
| the rise of the EV.
|
| I like Ars Technica's car coverage:
| https://arstechnica.com/cars/
| patmcc wrote:
| Eh, I'm not sufficiently qualified to explain relativistic time
| dilation, but I'm quite certain it exists and we can count on
| it.
| 0xDEAFBEAD wrote:
| >Most of the comment threads in this HN post are a lot more
| informative than the article
|
| To be fair, how many commenters on HN would accept a job in
| journalism if it was offered to them?
|
| We're lucky that so many qualified people share their takes for
| free on this website.
| Animats wrote:
| Older Tesla cars have a 12V battery for accessories, until the
| main high-voltage battery is turned on. So does this mean having
| a 48V accessory battery? Or what?
| bloggie wrote:
| I don't know much about the Cybertruck, but in general all
| modern cars, electrically propulsed or not, have a 12 V system
| which includes a battery for running electronics and some
| accessories. Very old cars had a 6 V system. There is a push to
| move to higher voltages, the battery would also be 48 V to
| match. https://my.avnet.com/abacus/resources/article/the-shift-
| to-4...
| Kirby64 wrote:
| Yes. Keeping the high voltage battery active is expensive, and
| also poses a (small) safety risk when the car is sitting.
|
| It's probably a modified version of the '16V' lithium battery
| in all other Teslas, just with 3x the pack voltage.
| etamponi wrote:
| If higher voltage leads to benefits, then why 48 and not 120 (US)
| or 230 (EU)? Or higher? What are the tradeoffs?
| jsight wrote:
| 48V still counts as "low voltage" for safety purposes. The
| lower voltage gets them increased safety when working with
| exposed wiring.
| callalex wrote:
| You are mixing AC and DC here.
| Moto7451 wrote:
| Audi also has a 48v architecture in use for mild hybrids like my
| SQ5. This is an older article but explains it well
| https://www.greencarcongress.com/2017/06/20170602-audi.html
|
| My 2021 is fully 48v except for an inverter for necessary 12v
| circuits (like cigarette outlets and the jumper pins) and a small
| motorcycle battery that is used for minimal 12v functionality.
| The mild hybrid battery is under the rear seats and spins the
| alternator to keep accessories running.
|
| https://www.autoweek.com/news/a36331077/48-volt-hybrid-syste...
|
| My guess is that handing this out is a very nice thing to do but
| perhaps irrelevant in a world where 400v and 800v drive systems
| are the state of the art. Those systems can't rely on the car
| body as a common ground for all sources of current and have a lot
| of inherent safety concerns that force a lot of electrical
| engineering that my old Camaro didn't need to have.
| arcticbull wrote:
| Most automotive parts are 12V so that just means due to economy
| of scale, 48V parts are more expensive. They are trying to
| reduce their cost basis by getting everyone to move over to a
| common, more efficient voltage spec. This is good industry
| advocacy.
| CodeWriter23 wrote:
| There's a crossover where ROI results in lower wiring costs.
| gleenn wrote:
| My understanding was that nearly every production vehicle on
| the road is 12V and that Tesla and perhaps Audi as you
| mentioned are doing things differently. Who is using 400-800V
| systems? That sounds extremely dangerous.
| Turskarama wrote:
| They're getting mixed up, the 400-800V systems are _only_ for
| the motors, everything else in the car still uses low
| voltage.
|
| In fact, afaik every single electric car has two separate
| systems. There's a high voltage system (the main battery and
| motor(s)) and the low voltage (almost always 12v) system,
| usually with a traditional lead-acid 12v battery that is
| charged via a DC-DC converter connected to the high voltage
| battery.
| Kirby64 wrote:
| Not true in most EVs regarding 'only the motors'. The
| AC/heat pump compressor is run off the HVDC, typically.
| Since it runs for long periods of time and consumes
| kilowatts, you want to run it straight off the main HV
| battery. Also, any vehicle that still uses resistive
| heating (older EVs tended to do this, Tesla included) use
| the HVDC for that.
| Moto7451 wrote:
| I'm speaking about the power planes. What they drive is
| irrelevant from the standpoint that higher voltage systems
| create safety issues that lower voltage systems do not
| have. No one is going to be ok with "occasionally being
| shocked by 48v" or "occasionally seeing arcing in their car
| from a high voltage system."
|
| Running 48v to a radio is not an engineering marvel.
| Running it safely and reliably in an automotive environment
| full of vibration and weather is.
|
| If you can do that with 400v, I argue you can do it with
| 48v, so the secret sauce they're sharing is less relevant
| than if they did this ten years ago.
| Turskarama wrote:
| I feel like you're mixing up points now, running 48V is
| fine _because_ the voltage is low enough that it's
| unlikely to kill anyone if you mess it up. The 400V
| system in the meantime has a lot more care taken and
| limiting the systems it works on to ONLY high power
| systems lessens the number of things that can go wrong.
| nine_k wrote:
| A ton of trucks are 24V, especially in EU. 48V in automotive
| industry is something new; I can't remember seeing it on any
| commercial trucks.
|
| Electric bikes use 12V, 24V, 28V and even 56V. Nobody loves
| the weight and the cost of thick copper wires.
|
| 400V or 800V are charging voltages, because it's the
| operation with the highest current; to keep it manageable
| while transferring more energy you need really high voltages.
| AFAICT, motors inside a Tesla use 320V. I suppose that ICE-
| electric hybrids also use some reasonably high voltage to
| feed the electric motors.
| dreamcompiler wrote:
| Tesla uses 800v only to run the Cybertruck's drive motors.
| Every other electric load in the truck uses 48v. Both of
| these are much higher in the Cybertruck than all other Tesla
| models. All other Tesla models use 400v [IIRC] for the drive
| motors and 12v for everything else.
| 1970-01-01 wrote:
| Newer builds are using 16v lithium batteries for low
| voltage.
| Kirby64 wrote:
| Pretty sure the AC/heat pump on the Cybertruck runs off the
| 800V pack. Since it consumes so much power for long periods
| of time, it makes little sense to run it off the 48V.
| Existing other Tesla's use the main pack voltage for
| AC/heat pump.
| dreamcompiler wrote:
| Good point and makes sense.
| inferiorhuman wrote:
| Mercedes introduced their 48V hybrid in 2016. Kia in 2018.
| Peugeot just introduced theirs this year.
|
| Jalopnik was talking about the "48V revolution" in 2017:
|
| https://jalopnik.com/everything-you-need-to-know-about-
| the-u...
| hef19898 wrote:
| At least once delivered early then? Sharing tech 6 years
| before their annoncement of sharing it!
|
| Alternative take: Everybody else was aware 48 V networks
| work as well for decades, there was just no real benefot in
| switching yet. And Tesla has nothing to do with it.
|
| What's next, Tesla annoncing they will share the
| revolutionary tech of windscreens and doors?
| SV_BubbleTime wrote:
| >Who is using 400-800V systems? That sounds extremely
| dangerous.
|
| Every electric vehicle. And yes, it is dangerous to work on
| the HV circuit.
| Moto7451 wrote:
| Not all of them. The Kia Niro I'm driving as a rental this
| week has a 240v battery. Level 3 charging it feels wildly
| slow compared to my car.
|
| But yes, you're right the increased voltages add a lot of
| risk that has to be managed.
| crishoj wrote:
| And, thankfully, high-voltage systems _are_ extremely
| well-managed in EVs.
|
| Evidence in support of this claim is that EVs are
| statistically 4-5 times less likely to catch on fire
| compared to ICE vehicles.
|
| https://gmauthority.com/blog/2023/11/ev-fires-less-
| likely-th...
| ReactiveJelly wrote:
| Not sure how relevant this is, but curious readers might be
| interested: In those 400-800 volt systems, the low-voltage
| system is used to wake up the battery's computer and close a
| normally-open contactor inside the battery that connects the
| high-voltage system.
|
| So indeed they might not ground HV stuff to the chassis, and
| the hundreds-of-volts sources are disconnected if the car is
| turned off and unplugged.
| crishoj wrote:
| Exactly. Apart from waking up the vehicle and closing the
| high voltage connectors, a whole myriad of things run off the
| low-voltage system, including lights, climate, infotainment
| and most (if not all) actuators.
| grecy wrote:
| > _This is an older article but explains it well_
|
| https://www.greencarcongress.com/2017/06/20170602-audi.html
|
| From the article:
|
| > The 12-volt system is connected to the main electrical system
| via a DC/DC converter
|
| > Audi also offers the new MHEV technology with the
| conventional 12-volt electrical system
|
| > 48-volt vehicle electrical system. In a different layout--
| without MHEV--the 48-volt constant voltage system already
| entered volume production in 2016 as the Audi SQ7 TDI. In this
| vehicle, the alternator still operates on a 12-volt basis, and
| a DC converter couples the 48-volt electrical subsystem
|
| > Small consumers such as control units or lights will remain
| in the 12-volt system well into the future, however
|
| The article makes it very clear that what Audi are doing is not
| similar to what Tesla have done with the Cybertruck. The
| Cybertruck has no 12v system, everything runs on 48v. The power
| seats. The seat heaters. The rear defroster, the interior
| lights, literally everything. They can have much smaller and
| lighter wires and use way less copper.
|
| Using a 48V system for a mild hybrid is very common, even Jeep
| do that.
| maxerickson wrote:
| Realistically, using 12 volt and 48 volt for accessory
| systems are pretty similar. 48 volts just reduces your
| current, and you have to design everything for ~56 volts
| instead of ~14. But it's not really a different exercise.
| grecy wrote:
| > _48 volts just reduces your current_
|
| "Just" is doing an awful lot of work in that sentence.
|
| Yes, moving from 12v to 48v reduces the current. That means
| you can have much smaller gauge wires, it means you lose a
| lot less power ( powerloss = (I _I)_ R ), it means you use
| a lot less copper and it means you save a lot of weight on
| wiring and connectors.
|
| That is literally the point.
| maxerickson wrote:
| Right, the reason to do it is obvious and the development
| work is straightforward, it's a step forward but it isn't
| something to get all breathless about.
| grecy wrote:
| Absolutely, Elon said that himself in the recent Munroe
| interview.
|
| It is just bringing car wiring into the 21st century.
| Moto7451 wrote:
| At least in the case of Audi it is more than just the starter
| used for the mild hybrid depending on market and
| configuration. On my generation/configuration of car it is
| also used to prespin the Turbo to avoid lag, it powers the
| active magnetic suspension, the AC compressor, and the power
| steering pump (annoyingly located between the feet of the
| driver and the seat where you can feel it when it runs).
|
| While you're right on the accessories voltage, In other
| comments I've made the point that I'm not trying to say
| anything about the merits of 48v accessories. Jim Farley and
| Elon's bromance aside, the tech exists within car companies.
| It's nice they shared but it's not like NACS where a real
| issue is being solved. Problems of driving aren't solved with
| 48v interior lights.
|
| Supply lines are a real challenge and why my Audi still has
| 12v heated seats despite having a 48v system available. The
| head unit is 12v. I'm guessing the speaker amp is 12v even
| though 48v would make that less challenging. They have a 12v
| only model that shares parts and they apparently didn't want
| to move everything to 48.
| grecy wrote:
| Sure, they use the 48v mild hybrid system to act like the
| ICE when the ice is not running to power some things that
| would be on the serpentine belt and need to keep spinning
| when the ICE is off. It's a slightly more fancy engine
| start/stop system.
|
| > _the tech exists within car companies_
|
| Of course. Elon said very clearly in the sandy munroe
| interview the move to 48v everything is nothing
| revolutionary, its just bringing vehicle wiring into the
| 21st century. Anyone could have done it, they just have not
| been able to pull it off before now.
|
| > _They have a 12v only model that shares parts and they
| apparently didn't want to move everything to 48._
|
| They couldn't move everything to 48v because their
| suppliers dictate what they can do, and that prevented
| them.
| dreamcompiler wrote:
| > except for an inverter for necessary 12v circuits
|
| Nitpick: That's a DC-DC _converter_ , not an inverter.
| bhauer wrote:
| > _My guess is that handing this out is a very nice thing to do
| but perhaps irrelevant in a world where 400v and 800v drive
| systems are the state of the art._
|
| The high-voltage system for the drive motors, whether 400V or
| 800V, is unrelated to the low-voltage system for accessories.
| The transition from 12V to 48V is concerning the low-voltage
| system. Prior to the Cybertruck, no automobile ever had a fully
| 48V low-voltage system. To learn more about how this is a big
| deal, check out Jason Cammisa's video on the subject. I've cued
| it to the specific topic in the [1] link below.
|
| [1] https://youtu.be/L6WDq0V5oBg?si=dbzsPMAkvmGiQQ8n&t=613
| sbierwagen wrote:
| >and the jumper pins
|
| It can be _started_ through the converter? That takes something
| like a hundred amps. It must be pretty beefy.
| phire wrote:
| No.
|
| For safety, hybrids and electric vehicles physically
| disconnect the high-voltage battery from everything when it's
| off with massive relays. So you can end up in the somewhat
| stupid situation where your high-voltage battery is fully
| charged, but you can't do anything because the tiny 12v
| motorcycle battery is flat.
|
| Starting simply requires enough 12v current to close a relay,
| the amps going though the "jumper pins" are tiny. And once
| the relay is closed, the high-voltage battery can keep the
| relay closed and charge the 12v battery via the dc-dc
| converter.
|
| The amount of current to "jump" a hybrid or electric car is
| so small that they really should just install a USB-C cable,
| so you could just use your phone to jump start it.
| sbierwagen wrote:
| That describes the situation where the 12V battery is flat
| but the HV battery is charged. But what happens if the HV
| battery is flat on a non-plug in hybrid? Can it be charged
| from 12V?
| ace2358 wrote:
| Wouldn't you just start the car if the HV was flat and
| the LV was charged?
|
| If they're both flat I agree, I'm curious what you do.
| phire wrote:
| There is no 12v starter motor, it always just uses one of
| the large motor-generator units to start the engine, and
| in the Prius drive chain, they require 600v (boosted from
| 200v from the HV battery).
|
| So if the HV battery is flat, you can't start the engine
| to charge it.
| ace2358 wrote:
| Wild! Thanks!
| phire wrote:
| Yeah, I started wondering the same thing as I was writing
| that response, as I do actually own a Lexus with the
| Prius drive chain.
|
| For starters, it would be pretty hard to get into that
| state in the first place. My understanding is they
| actually report a 10% or 20% charged battery as
| "completely empty". And the it's completely disconnected,
| so it shouldn't discharge much.
|
| Looking though the service manual, there doesn't even
| seem to be an error code for "HV battery low", nor any
| mention of the DC-DC converter being able to charge the
| HV battery from 12v, it only goes from HV to 12v.
|
| So I really suspect if you do happen to end up with a
| flat HV battery that's too flat to start the engine, it's
| just going to flash the "Replace HV battery" error code.
| Theoretically, someone with the right tools could
| disassemble the battery and charge the individual
| modules.
|
| And the only speculation I can find on google is that
| "flat HV batteries are very rare" and probably only
| happen when the HV battery has other issues and needs
| replacement.
|
| Edit: After more googling, apparently Toyota dealers have
| a special charger called the THS that can charge the HV
| battery in non-plugin hybrids.
| tw04 wrote:
| No. Nobody is putting in a 12v to 400v dc to dc
| converter. There would be no point. I haven't done the
| math but I'd be surprised if you got more than a couple
| miles out of it. If your high voltage battery is
| completely dead, you're calling a tow truck.
| Moto7451 wrote:
| In the case of my Audi, the starter motor is 48v so the 12v
| system charges the 48v system enough to start.
|
| In EVs the 12v system is used to power a contactor that
| connects the EV battery to the drive system. That's the
| clicking sound you hear on power on and power off and another
| contactor can be heard clicking during charging.
| codeulike wrote:
| Its not that same, that Audi still had a 12V system because all
| the commodity parts (control units, interior lights) are built
| to run on 12V. What Tesla are doing is getting rid of 12V
| entirely so that every little window raising motor or interior
| light or actuator to move the seats is running on a 48V system.
| MrVitaliy wrote:
| PoE over CAN bus moves more complexity from EE world into
| software world. While Tesla currently has best auto software,
| this is still a very foreign and a different way of
| thinking/managing for traditional auto manufacturing. This won't
| be just using a different set of cables, it's going to flip their
| engineering departments upside down.
| klysm wrote:
| Wouldn't it be PoC instead of PoE?
| Trex_Egg wrote:
| Power over Ethernet (PoE) is a technique for delivering DC
| power to devices over copper Ethernet cabling, eliminating
| the need for separate power supplies and outlets.
|
| Source: https://www.google.com/url?q=https://www.cisco.com/c/
| en/us/s...
| mmaunder wrote:
| Many comments here seem to be confusing the accessories circuit
| voltage with the electrical vehicle motor and drive system. The
| vehicle motors have a combined power output of 450KW which
| requires a high voltage 800V system or the wiring would be so
| heavy it would not be feasible.
|
| This spec appears to be the accessories circuit with Tesla
| pushing for a new 48V standard. That's super smart because it
| immediately means you need roughly a quarter of the metal in
| wiring that you needed previously. It's cheaper, lighter and more
| environmentally friendly. And it enables the use of higher power
| devices. If you've ever had to wire your 1000W sub woofer amp
| directly to your battery you know what I'm talking about.
|
| It's worth noting that newer GA aircraft like Cessna 172 use a 24
| volt system. So non 12V systems for accessory power isn't a
| totally new idea. And older 172s have 12 volt systems. So the
| transition was made in that space anyway.
| hatsunearu wrote:
| A lot of commercial trucks use 24V systems also.
| maxerickson wrote:
| Stuff like buses have used 24 volt for ages. Basically anywhere
| with larger accessory loads.
|
| 48 volt has been 'on the radar' in automotive spaces for a
| couple decades.
| bigdict wrote:
| Dumb question but why does deciding to run at a higher voltage
| decrease the amount of wiring necessary? And why not increase
| it even further then?
| kalleboo wrote:
| Watts = Amps * Volts (or, more scientifically, P = I * V)
|
| If something draws 48 Watts of power, you can either supply
| it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt.
|
| It's the amps that determine how thick the wiring needs to
| be, so by lowering the amperage, you lower the amount of
| wiring needed.
|
| I believe the only reason cars are 12 V is because that's a
| practical voltage to build lead-acid batteries at (which is
| actually closer to 14 V in practice). Early car electric
| systems were only 6 V back when the only accessories were the
| front lights and the horn, but as more stuff was added on
| cars moved to 12 V.
| ace2358 wrote:
| Things like stator motors were also probably quite
| difficult to do at 6v.
|
| I know the older Honda CT110 postie bikes came in 6v in the
| old days. That was a kick start.
| grepfru_it wrote:
| Car electrical systems typically run at 13.8-14.4V while
| the alternator is charging and drops slightly after the
| battery is topped off. When the engine is off the battery
| regulates a 12v output
| loufe wrote:
| Resistance is proportional to the square of current. This
| would mean 1/16th the loss instead of 1/4th.
| 05 wrote:
| Nope. Consumed power is voltage*amperage, and it's
| constant, so 4x more voltage means 1/4 the amps. Wire
| heating is I squared R, so with both I reduced and R
| increased the losses are just 1/4, not 1/16 of the 12V
| system. Because you wouldn't keep the same wire gauges
| you've had in the 12V system, you'd reduce them to
| actually have some benefits from conversion.
| ahepp wrote:
| Isn't the resistance of a wire usually modeled as a
| constant value?
|
| Power dissipated in the wire as heat is proportional to
| the square of the current. It's equal to the voltage drop
| times current (P = I * V). Voltage drop is current times
| resistance (V = I * R). So P = I^2 * R.
| LoganDark wrote:
| This makes such little sense to me. I'm probably just
| stupid, but if the same amount of power is flowing through
| the wire, don't you need the same size of wire? A higher
| voltage system will push more energy through the same
| component, so you need thicker wires. If you up the
| resistance of the component to consume the same amount of
| energy as before, you arrive at the same size of wire you
| were using before, don't you?
|
| What exactly is magical about higher voltages that makes
| them suddenly able to carry more power across the exact
| same wire? I know you just said it's "lower amperage" but I
| don't understand how amperage can be the only thing
| dictating the required size of a wire.
| hansvm wrote:
| A higher voltage system enables the same energy at a
| lower amperage, so constrained to wanting to do a
| particular thing (loud stereo, bright headlights, ...),
| higher voltages result in lower amperages. I'll opt to
| not try to explain that intuitively, hoping that somebody
| else chimes in.
|
| For the other half, "why do amps determine wire size?"
| Amps are coulombs per second -- how much electrical stuff
| moves through a cross section in a second. The amount of
| heat produced is directly proportional to amperage (every
| bit of movement has a chance to whack into something and
| produce heat, and more movement per second or more
| seconds generates more heat). Wire size is ultimately
| constrained by being able to release that heat while
| still acting like a wire (not melting, not sublimating,
| still conducting, not setting anything else on fire,
| ...). The amount of heat released is proportional to
| surface area (proportional to the square root of
| diameter, but that difference doesn't matter a ton right
| now), and the amount of heat produced is proportional to
| amperage and approximately nothing else. The point where
| those two terms are equal is the limit for the system
| (engineers add in huge safety factors to account for
| conduit and insulation and other imperfections), above
| which your wire melts and below which it behaves
| reasonably. Higher amperages require higher surface area
| to release the extra heat (so much higher thicknesses),
| so a given amount of power (stuff you want your
| electrical system to do) requires lower amps or thicker
| wires to work appropriately, because you can achieve the
| same power by increasing the voltage on the same
| amperage, thereby solving your power problems without
| extra heat.
| hansvm wrote:
| Edit: Heat released is also proportional to the
| temperature differential between the wire and the outside
| world, as well as a constant associated with how well
| it's thermally insulated. The wire temperature rises till
| either some sort of breakdown occurs or that rate of heat
| release balances the rate of heat production. The spirit
| of that original comment is correct, but this feels like
| a nuance that might matter to somebody new to the topic.
| kukkamario wrote:
| The power loss by the resistance scales in the square of
| the current and linearly to the resistance. So doubling
| voltage reduces resistance power loss to one quarter so
| you could lower wire size and increase its resistance to
| double and still resistance power loss would be halved
| rcxdude wrote:
| What matters is energy but what's being carried by the
| wire is charge. A given amount of charge can have more or
| less energy, which is what voltage is. So if you give
| each unit of charge more energy then you can carry more
| power by only moving the same amount of charge. You get a
| similar thing in mechanical systems: a shaft is sized
| based on the maximum amount of torque it can withstand,
| but the amount of power going through it also depends on
| the RPM. More RPM = more power, for the same amount of
| torque, so if you are for some reason limited in the size
| of the shaft, you can use a gearing mechanism to rotate
| it faster and then gear down the other side and get more
| power through a smaller shaft. It's just that in
| mechanical systems gears are a lot less convenient than
| changing voltages is in electrical systems.
|
| (RPM and voltage are in fact related in EVs as well:
| generally speaking a higher voltage motor will be able to
| produce more power for the same amount of space and
| materials, but mostly by spinning faster, not producting
| more torque. You then need to gear it down to be
| practical in a car. But the trend is that things that
| make higher voltages and higher RPMs possible (the
| technology in transistors, insulation, bearings) are
| already cheap or getting cheaper, while things that make
| higher currents and torques possible (generally more raw
| material like copper and steel) are staying the same or
| getting more expensive. So EVs in general are pushing to
| higher voltages for lots of things)
| kzrdude wrote:
| Just as further confirmation, remember that long distance
| power delivery uses high voltage, often measured in
| kilovolts. Because of reduced losses that way.
| dgfitz wrote:
| Higher the voltage the lower the amp draw, so smaller wires
| can be used.
| pertymcpert wrote:
| For your first question, power = voltage x current. To
| transmit the same power, if you double the voltage you only
| need half the current. This is important because the
| resistance losses in conductors are related to the current
| not voltage, so you can use thinner wires without
| overheating.
| maxerickson wrote:
| 60 volts DC is a safety threshold. You start to move current
| through tissue at higher voltages.
| exclusiv wrote:
| Yes but state of your body/skin (R) and current (I) is what
| matters with regard to 60 volts being really dangerous
| (also the current path as the article below states).
|
| 60 volts is nothing UNLESS you are completely wet or
| sweaty.
|
| "It is estimated at 150 ohms for completely wet skin (in
| water), 1000 ohms for sweaty skin, and 100,000 ohms to
| 500,000 ohms for dry skin."
|
| Assuming a worst-case scenario with dry skin providing a
| resistance of 100,000 ohms, fatality becomes a possibility
| if the current exceeds 50 mAmp.
|
| Therefore, the lethal voltage would be above 0.05 (50
| mAmp)x100,000=5000 Volts. [1]
|
| So if you are wet or sweaty, it could be 7.5V to 50V that
| gets dangerous.
|
| So it makes sense why 60 volts is a safety threshold,
| especially for those that live in Florida or Arizona.
|
| [1] https://www.scienceabc.com/humans/how-many-volts-amps-
| kill-y...
| SV_BubbleTime wrote:
| > 60 volts is nothing UNLESS you are completely wet or
| sweaty.
|
| Ha, it's always easy to tell when people have experience
| with these things.
|
| Doorbell wiring is 48V. Go hold those in each hand and
| tell me how impossible it is to feel if your hands are
| dry.
| sokoloff wrote:
| Doorbell voltage in the US is typically 12V or 24V AC in
| the US. I can't feel that with dry hands.
|
| You might be confused with POTS (landline phone service)
| which is 48V DC with all phones not in use.
| mythhabit wrote:
| > 60 volts is nothing UNLESS you are completely wet or
| sweaty.
|
| From experience I'm not touching 60v, sweaty or dry as
| sand - that voltage hurts! And 48v is seriously
| uncomfortable. People have died from less DC voltage in
| industrial settings.
|
| Following EN61010, the max safe DC voltage in laboratory
| equipment is 35v for wet locations. For a car, we ought
| to assume that being wet is a possibility.
| stephen_g wrote:
| 48V is good because a lot of safety standards have the cut
| off for 'extra-low voltage' at 60V DC, gives you a bit of
| margin (when battery charging it pushes up to be in the 50s
| for example). Some battery systems I've seen at 56 volts
| nominal too. so sometimes people do have a bit higher-voltage
| ELV systems.
|
| 48V still lets you touch both conductors with dry hands and
| it's still very unlikely for you to be able to get any
| current to flow through you, you can't even feel it (although
| with safe working practices you'd only touch either positive
| or negative at one time, not both). Obviously it's very much
| _not_ the case to be able to touch the 800V conductors safely
| in the traction systems in EVs, that side is extremely
| dangerous and requires extreme caution and safety procedures!
| jeffrallen wrote:
| > requires extreme caution and safety procedures
|
| As long as the battery pack is still sealed and the
| interlock systems are undamaged and working correctly, it's
| no big deal. You follow the manufacturer's instructions to
| make it safe, then work on it like there's no voltage
| present.
|
| If the battery pack is broken or a prototype or whatever,
| yeah, then you need to think things through carefully
| before doing them. And have a plan for what you're going to
| do when things go wrong.
|
| Source: I work in electric aviation and work on battery
| packs.
| sokoloff wrote:
| GP was talking about the low voltage system (the 12-volt
| system in most cars) and choosing a voltage for it, not
| anything about the traction battery.
| carstenhag wrote:
| No, they were comparing the difference in precautions
| between 12/48v accessory battery and the 400/800V
| traction battery.
| sokoloff wrote:
| You are correct; thanks; I missed the precise context of
| the snipped text.
| formerly_proven wrote:
| If you can't feel 48 V with your hands I'd recommend
| moisturizer, because you have very dry skin.
| fastball wrote:
| You've already gotten a bunch of answers but to be honest I
| find all of them a little incomplete if you don't have any
| electrical background, so here is my attempt to be quite
| thorough from (almost) first principles.
|
| ---
|
| The equation for power delivered by an ideal system is P =
| IV, or power (P) = current (I) * voltage (V). Power is
| measured in watts, and that is generally the overall number
| that matters, in terms of what you can run off of your system
| at the same time.
|
| So to increase the wattage (power) of your system you can
| either increase the voltage or the current.
|
| - Increasing the voltage of a system increases the amount of
| resistance it can "break through". In "danger to human"
| terms, our skin is generally not a great conductor, so
| voltages lower than 50V usually won't enter the body (read:
| vital organs) at all. Voltages above 50V will start to enter
| the body depending on conditions, which is when electricity
| becomes much more dangerous.
|
| - However even if the voltage is high enough to enter the
| body, if the current (I) isn't very high it still won't be
| dangerous. Current is measured in Amperes (A), and the usual
| number at which a current _inside_ the body becomes dangerous
| is above 30mA. 30mA can cause respiratory failure if it
| passes through the lungs, current as low as 100mA can cause
| cardiac arrest if it passes through the heart. In a car 's
| electrical system, the currents we're operating with are
| definitely going to be over the 30mA threshold we just
| established, so we want to keep the voltage under 50V
| instead.
|
| Anyway back to cars and ignoring danger to humans for a
| second. Resistance is the main thing you want to overcome
| when it comes to the efficiency of such a system. The
| equation for power loss is P = I^2 * R, or "power dissipated
| (as heat) is proportional to the square of the current times
| the resistance". So if you increase the current of your
| system (in order to deliver more watts) you will also
| increase the amount of power you lose as heat. You can
| decrease the loss by decreasing the Resistance.
|
| The equation for resistance through a material is: R = r *
| (L/A), or Resistance = resistivity (an innate property of the
| material) * Length / Area. In other words, the longer your
| wire is the more current you will lose to resistance. But if
| you increase the cross-sectional area of your wire (A) by
| making the wires thicker, you decrease the resistance.
|
| So in short: if you have a high current (amperage) system,
| you use thicker wires in order to ameliorate resistive heat
| loss. But you can alternatively just decrease the amperage to
| reduce your resistive heat loss, which means thinner (and
| therefore much lighter) wires. But then you need to increase
| the voltage of your system in order to offset the power
| you're losing by decreasing the current. If you increase the
| voltage by 4x, from 12V to to 48V, this keeps it under the
| human danger zone (of 50-60V) and means your wires can be up
| to 16x thinner, taking up less space and less weight. Having
| it be a nice multiple of the previous system (4x) should make
| upgrading the relevant circuits a little more straightforward
| as well.
| elif wrote:
| The reason to not keep going higher is purely practicality
| because stepping down bigger voltage gaps for lower voltage
| applications begins to become less efficient/more waste heat.
|
| If you design 100v computers, monitor, headlights, seat
| adjustment motors, window/windshield motors, pumps, etc. you
| could cut these 48v wires in half again but if you end up
| stepping everything down anyway it loses its utility.
|
| The safety rules about voltage and the human body are often
| poorly overstated, as is the addage that 'its the amps that
| kill you, not the volts.' in reality it takes a whole lot of
| both [0].
|
| As further research, here[1] is styropyro touching 2 contacts
| which have more current than the largest bolts of lightning
| (enough to almost instantly vaporize a crowbar) with his bare
| hands, but because it is 12V it is not able to pass through
| him.
|
| [0] https://youtu.be/BGD-oSwJv3E
|
| [1] https://youtu.be/ywaTX-nLm6Y
| ianlevesque wrote:
| Just don't try that with wet hands.
| Dylan16807 wrote:
| Even with wet hands it's hard to get much out of 12v.
| injb wrote:
| As an analogy, if you have a hose squirting out water at a
| certain rate, and you increase the pressure, then all other
| things being equal you'll get a higher rate of water. But
| then that means you could now reduce the size of the hose,
| keeping the new higher pressure, and achieve the original
| rate of water delivery with a smaller, cheaper, lighter hose.
|
| It's very similar with electricy: water pressure is voltage
| and the rate of water delivery is power.
| the_gipsy wrote:
| Bad analogy: for the electrons, Volts are (inverse) latency,
| and wire thickness is maximum bandwidth (or max amp). That
| is, make electrons go faster, instead of pushing more
| electrons at the same time.
|
| Of course none of this really makes sense, for example you
| can't increase wire thickness to increase amps etc.
| DannyBee wrote:
| 48V has been considered for automotive for decades. The problem
| was not know how.
|
| It simply has never been worth it before to retool things in
| practice.
|
| It's also electrically a lot more noisy. The limit of what is
| considered low volt is like 60v or something.
| klysm wrote:
| Why is it inherently noisier?
| horacemorace wrote:
| Faster slew rate for all switch supplies in the system.
| Nothing directly runs 48v.
| klysm wrote:
| I'm still skeptical. Why can't it be filtered out
| yetihehe wrote:
| It can, it just requires up to a dollar more per device.
| ferongr wrote:
| Nothing "directly" runs on 12V either. All electronics
| will have stepdown converters in both the 12V and 48V use
| case. Motors, solenoids and incandescent bulbs can be
| made to work with either voltage (the same way we do for
| 24V systems in heavy goods vehicles here in Europe).
| bsder wrote:
| Not true.
|
| Your motors and actuators operate directly on 48V (in
| fact, most actuators would prefer a higher voltage like
| 96V). That's really significant.
|
| Microelectronics is effectively a "don't care" since
| everything is behind a regulator or a PHY.
|
| Yeah, 48V tolerant switching regulators are going to be a
| bit more expensive until the volume gets rolling, but
| that problem solves itself while ethernet and CAN PHY
| chips are already 48V tolerant.
| jojobas wrote:
| Lights and motors can easily take 48V. It's only the
| digital devices that require switching supplies, and
| that's still much better that 200-300V rectified mains
| power.
| jdewerd wrote:
| It was never worth it to retool _for decades_?
|
| Or was there a pathological lock-in between suppliers and
| manufacturers that prevented even the most obvious
| innovations from happening if they required any amount of
| coordination?
| hef19898 wrote:
| Since car manufacturing, and design, wasn't held back at
| all by something like auxiliary current, the reason more
| likely was people not wanting to waste energy to improve on
| something that is working just fine for everyone.
| Closi wrote:
| Well according to Tesla it wasn't working just fine for
| everyone - they have been able to massively simplify
| their internal wiring.
|
| Classic example of legacy automakers happy to maintain
| the status-quo because it is easiest, while the new kid
| on the block is pointing out that things don't have to be
| the way they are just because they are that way.
| panick21_ wrote:
| Its the same with aluminum casting. The car makers used
| the technology once in a while in some specific parts,
| Tesla was like 'why not make half the car out of one
| casting'.
|
| Tesla worked closely with a supplier, did lots of its own
| research and development and continue to work with a
| supplier to make the technology better over time.
|
| This was considered stupid at first. This is now very
| widely copied. First automakers from China copied it. And
| now others are copying it as well. Even Toyota (who
| everybody believes are some kind of gods of
| manufacturing) are copying this now.
|
| If you have been doing something one way for long enough,
| going into a radically different direction is hard. Your
| whole workforce knows about welding steel sheets
| together, and nobody knows anything about casting. Your
| whole workforce knows about V12 and the ecosystem for
| that.
|
| Its hard to fundamentally change how you do things when
| you are producing millions of vehicles a year.
| hef19898 wrote:
| A quick search turned up this:
|
| >> S&P Global Mobility forecasts 15% to 20% of
| traditional body-in-white (BIW) stampings in 2030 may be
| at risk from these gigacastings. Underbody components
| typically comprise about 50% of a vehicle's BIW shell,
| and this soft underbelly is the target of gigacasting's
| focus.
|
| Source: https://www.spglobal.com/mobility/en/research-
| analysis/gigac...
|
| Obviously not a technical journal, nor did I double check
| anything.
|
| What the numbers say 15-20% _might_ be replaced by
| gigastampings (sidenote: I ak surprised Elon didn 't
| rename Twitter to Giga-X). Which, ok, is a thing. But
| nowhere near the revolution people seem to believe.
| First, it has to happen. Second, others have to consider
| it better, read overall cheaper, and continue doing it.
| _Then_ we can properly judge. Until then, it might as
| well be in the category of Teslas fully automated
| factories that ended with Elon doing pyjama parties with
| his workers on the shopfloor and ad-hoc tents.
|
| And Toyota, as per the linked article, is not _copying
| it_ , they are "eyeing" it. And believe itbor not,
| manufacturers are eyeing new production tech all the
| time.
|
| And Toyotas reputation in _car_ manufacturing is well
| earned.
| panick21_ wrote:
| You are underestimating how long things take in the car
| industry. 2030 is really, really soon.
|
| The majority of cars sold then will be existing models
| with minor updates.
|
| And car companies only upgrade their major platforms
| every 5-7 years. Many companies are currently planning
| their second (or first real) EV platform.
|
| But by 2030 even the waste number of EV will be on first
| generation EV platforms still.
|
| Companies have 100s of million invested in their current
| body lines. So unless you build a totally new factory you
| are not gone adopt this technology.
|
| When Toyota came out with their production system it took
| decades for all the practices to become established.
| hef19898 wrote:
| I'm more an aerospace guy, but I am fully aware of the
| time scale around production technology changes. Thing is
| so, 2030 is an estimate, not a commitment. And I didn't
| find anything about actual investments or announcememts
| from OEMs around that.
|
| Also, 20% of castings still means a _lot_ of welding
| before a car body is made.
|
| One thing regarding Toyotas production _system_ so: it is
| all about management and processes and not about the
| actual machinery. And it share a lot of principles
| ranging as far back as Venice 's Arsenal in the 16/17th
| century and, especially, WW2 mass manifavturing of, e.g.,
| planes.
|
| Anothet major difference: TPS is a proven methodology for
| longer than Tesla, let alone any production tech coming
| out of Tesla, exists as a company.
| wil421 wrote:
| Legacy automakers have no need for a 48v system. Most
| vehicles have an ICEs and they will for the next
| decade(s) as EV and PHEV adoption rises. 12 years is the
| average age for cars in the EU/US.
|
| Why would they upgrade a system when they don't need to?
| Tesla can be a front runner and companies like Bosch will
| start creating 48v parts as EVs become more popular for
| legacy auto to use.
| wayfinder wrote:
| I mean there have always been a market for 48V components.
| The problem is that the market is much smaller so as a
| customer, you're paying a lot more and it's hard to justify
| raising the price of your car because you decided to go
| 48V.
| brnt wrote:
| Try counting the number of businesses involved in making a
| vehicle.
| arghwhat wrote:
| 24V is common in trucks, and yet never made it to regular
| cars because there was never _sufficient_ reason.
|
| Using a higher voltage is not an innovation (it's an
| obvious change, and we've gone from 6V to 12V to, in some
| cases, 24V already) - rather it's just a slight efficiency
| improvement in largely non-critical systems, with not a
| _lot_ of incentive to take on the cost of transition.
|
| In a a personal ICE vehicle, the only _real_ significant
| power was to the starter motor and from the generator, and
| the distance there was short so the copper didn 't really
| matter and thus no one cared for 24V - unlike industry
| where you might have significant aux systems. With EVs, you
| have heat pumps and brake boosters on the auxillary power,
| so you now have a stronger driver for conversion.
|
| Even within 12V, you'd get a larger weight reduction from
| not carrying an aux _battery_ , and just feeding through a
| converter from the HV system.
| hulitu wrote:
| > The limit of what is considered low volt is like 60v or
| something.
|
| As far as i know, 60 V is the limit for alternating current.
| For DC it is 24 V.
| RF_Savage wrote:
| Depends on the region. 56V AC and 72V DC here. -48V has
| been the standard voltage in telecoms for +100years, so 48V
| systems and parts are not that exotic.
| avalys wrote:
| Mercedes-Benz has been using 48V systems since 2016.
|
| https://paultan.org/2016/10/31/mercedes-benz-reveals-
| first-d...
|
| This dynamic, where Tesla "announces" something that the rest
| of the industry has been doing for a while anyway, and a
| bunch of star-struck enthusiasts and stock manipulators tout
| it as an example of Tesla' "super smart innovation", is
| getting tiresome.
| panick21_ wrote:
| That's a complete misunderstanding of what Tesla did.
| Having a component in the car that is 48V and having the
| whole car being on a 48V PoE architecture are totally
| different things. The sad part is that these company
| actually have the beginning of a 48V system but never
| actually pushed threw and did it all.
|
| This is like when SpaceX landed a first stage and everybody
| was like 'DC-X did it SpaceX did nothing new'.
|
| There is a reason lots of people, including experts are
| exited of what Tesla did here.
| mikeyouse wrote:
| Of course Tesla has taken it further which is interesting
| and could be useful - but it's not quite true that the
| whole car is on 48V, they've already said that ~20% of
| the common / supplier-provided components are still 12V.
| For pure EVs, sticking with higher voltage makes a lot of
| sense and Tesla was perfectly suited to lead the charge
| here since they have built so much of their supply chain
| from scratch and can spec everything to be 48V where
| other EV manufacturers mostly just reused components from
| their ICE cars.
|
| Previous 48V systems were only partial for good reason as
| well - traditional manufacturers have been using "mild
| hybrid" 48V systems since ~2001. Many of the electrical
| components on ICE vehicles are parasitic engine loads
| since they need power than can be provided with 12V, so
| e.g. the water pump and AC compressor have separate belts
| that always are 'robbing' the engine power regardless if
| they're needed or not. Adding that 48V system allows for
| the engine to be freed from the draw that those
| components require and adding some light regenerative
| braking is sufficient to keep the batteries supplying
| that system charged.
|
| That these 48v systems aren't universal should provide
| some color on how successful / important the
| manufacturers had found them to be.
| t0mas88 wrote:
| Jup happens all the time. Tesla also made the CyberTruck a
| drive by wire system, now fans are claiming it has the
| unique ability to have variable steering angles based on
| speed which is "far ahead of any other manufacturer"
|
| Except that BMW 5-series and 7-series from 2010 onward have
| had this option... They've done it in a smarter way using a
| plantery gear system to keep a physical steering wheel
| connection as a backup instead of going the cheap and less
| safe drive by wire way that Tesla put on the CyberTruck.
| ironyholder wrote:
| That is a link to a press release. As best as I can tell
| from other sources, they started shipping some high end,
| low volume models the next year that added _a separate 48V_
| curcuit in addition to the 12V. Color me impressed...
| xenadu02 wrote:
| There is still a large benefit to this. Because Tesla is
| seen as a leader in the EV space it prods others to follow
| them. In some cases like this it gives people in the supply
| chain or internally at other automakers justification to
| make changes they've been prevented from making in the
| past.
|
| All sorts of people have all sorts of random ideas that
| never go anywhere until an industry "golden child" says
| it's the way forward. Without that effect the change can
| take much longer to happen.
| petre wrote:
| How is DC more noisy?
| rkagerer wrote:
| 48V is also used on some boats (eg. certain trolling motors)
| user_named wrote:
| "super smart" - more like completely obvious to everyone for
| decades
| szundi wrote:
| That's what Elon said, no innovation, just made the step
| avalys wrote:
| Two seconds of googling shows that Mercedes did this first
| in 2016, if not earlier.
|
| https://paultan.org/2016/10/31/mercedes-benz-reveals-
| first-d...
|
| Elon is a serial confabulist and bullshit artist.
| panick21_ wrote:
| As usual whenever Elon is involved people turn of their
| brains just so they can not admit that Elon or his
| companies did something well.
|
| Nobody says this is the first time V48 has ever been used
| for anything. That literally just missing the point.
|
| The point is that the whole architecture of the car will
| use PoE 48v.
|
| And if you go and take apart these Mercedes cars you will
| see that the waste majority of all of the devices and the
| wiring use the exact same 12v architecture that all the
| ICE cars also use.
| davedx wrote:
| That seems to be the engine not the entire electrical
| loom?
| memish wrote:
| He's an engineeer that worked through this with other
| engineers from first principles.
|
| You're spreading bullshit with 2 seconds of effort.
| margalabargala wrote:
| > He's an engineer that worked through this with other
| engineers
|
| Who? Because you can't mean Elon, not if your objection
| is to people spreading bullshit...
| hulitu wrote:
| > Tesla pushing for a new 48V standard. That's super smart
|
| 48V is a dangerous voltage. Better not touch any wire.
| teknico wrote:
| > 1000W sub woofer amp Your car subwoofer is surely not so
| stiff that it needs so much power. But after using it, your
| ears will definitely be.
| MrBuddyCasino wrote:
| 48V is also currently used on the supporting electric traction
| motor of "Mild Hybrid" cars.
| lmpdev wrote:
| I get this a lot
|
| I work at an electronics store in Australia
|
| This week I had a customer dumbfounded why his 3,500W inverter
| almost caught fire
|
| He was using 8-gauge wire (~56A max)
|
| He needed 00-gauge (almost 300A max)
|
| If he'd have run the system at 48V instead of 12V he'd have
| saved $200+ per metre on cabling his inverter
|
| My advice on voltage selection for a vehicle is once you're
| needing more than a few metres of 0-gauge, you should possibly
| increase the voltage of the system
|
| High current cabling means expensive ANL, mega or other high
| performance fuses or other expensive circuit protection methods
|
| I strongly believe that 48V systems are inherently safer than
| 12V systems when it comes to the public doing DIY work
| hef19898 wrote:
| Good look doing DIY work on the 48V network of a modern car,
| ICE or EV or 12, 24 or 48 V doesn't matter.
|
| And the past 12 V systems are dead easy to work on. On older
| cars that is, as soon as you have electronics and bus systems
| DIY basically requires deep car electronics knowledge and
| skills.
| jakewins wrote:
| Do you have examples of what kind of DIY work is hard?
|
| I haven't done a ton of work on newer cars, but at least
| adding wiring for a hitch on my Kona EV was just as easy as
| any wiring I've done on my old truck.
|
| Is a job like adding amps and better speakers trickier?
| RamblingCTO wrote:
| I have a defender and added a bunch of stuff to it:
| cruise control, motor pre-heater, rear camera, working
| lights in the rear. I'll also add a diesel heater and
| more electrics at some point. On 12V it's easy, can't
| imagine doing work like that with 48V. Not sure how this
| works, and if you maybe just can use 12V anyway. But
| wanted to make the point of camper vans and overlanders
| and offroaders.
| hef19898 wrote:
| An old or a new one?
| RamblingCTO wrote:
| Ah right, should've specified that. Of course an old one
| ;) A Td5. I call the other one "New Defender"
| hef19898 wrote:
| And a TD5 is already modern-ish enough, but very nice
| regardless! Personally, I would be at a loss working in
| anything built after the early 80s, so for a Defender
| that would be the dual-carb V8s, and 200/300 TDis.
|
| My 1982 Range Rover has all of three fuses, so
| electrically I'm fine! Except the mess previous owners
| did to the original wiring... No idea why it is so
| difficult to just make your own wiring for after market
| accesories instead of butchering the OEM one up beyond
| recognition. It works, so I don't touch it. I have no
| idea _why_ it works so...
| RamblingCTO wrote:
| Yeah I don't touch anything in the box beneath the
| passenger front seat ;) The previous owner thankfully
| already fixed the "oil creeps up the wires" issue, so I
| can leave it. Nothing I'm too keen on, but simple enough
| I figure.
|
| > I have no idea why it works so...
|
| I know that feeling haha. Adding wiring is so much easier
| than ripping up existing stuff ...
| hef19898 wrote:
| When a mechanic from Land Rover saw the wiring, he said
| something along the lines of "just fault location would
| be 2k, none of the colors I see should be there". A
| mess... But hey, the 80s and 90s were a wild time, and it
| is rust free!
| hef19898 wrote:
| Depends on where you connect stuff. Directly to some
| wiring loom that is already there? Bad idea, not all
| connected equipment will take the aditional loads well.
| Going directly to the car battery with dedicated wiring?
| Doable, but since start-stop is a thing, battery
| management and other stuff migjt not like that very well
| neither. Second batery? A bitch since start-stopp.
|
| Hence, one needs some good knowledge around that, what to
| connect where.
|
| In the old days, well, just go directly to the main
| battery with your aftermarket wiring and Bob's your
| uncle.
|
| And none of that, battery management, which equipment can
| be connected where, has anything to do with the voltage
| but rather with all the other stuff modern cars have (bus
| management, battery management, ECus,...) all of which
| might or might not accept voltage and amp fluctuations
| very well.
| davedx wrote:
| Dead easy is relative I guess, I once tried to track down
| an issue with the wiring loom of my 400cc motorbike and
| ended up giving up...
| cabalamat wrote:
| > as soon as you have electronics and bus systems DIY
| basically requires deep car electronics knowledge and
| skills.
|
| So how is this done on cars? Dores each manufacturer have
| their own proprietary bus system (what i imagine), or is
| there a standard that everyone can use?
| sejl wrote:
| I guess you work at Jaycar too? Always a fun conversation
| trying to explain voltage drop to someone who wants to cheap
| out on cable with our inverters and DC/DC chargers.
|
| I'm sure a 48V bus would solve all those F1 errors too.
| LilBytes wrote:
| That's funny, I assumed the same.
|
| Not an employee, but a very happy reoccurring customer.
| linsomniac wrote:
| Back in the '80s I was helping a buddy upgrade the stereo
| system in his RX-7. The teenager down the street comes by and
| educates us that "you should be using really thin wire, like
| telephone wire, because otherwise the amp sucks all your
| power." My buddy was an electrical engineer at Hewlett-
| Packard.
| bigallen wrote:
| How do you integrate the 48V system with the existing 12V
| system when doing aftermarket/DIY work? Do you add a 48V
| inverter? A buck-boost DC-DC converter? between the battery
| (or main fuse block) and the 48V system?
| petre wrote:
| You don't. 48V battery and separate circuits if it's an RV,
| otherwise forget it.
| Panzer04 wrote:
| Given the choice almost any EE would probably pick the higher
| voltage system for cost saving reasons, but I imagine they were
| mostly constrained by legacy compatibility requirements here.
|
| It'a "smart", but there are probably reasons it hasn't already
| changed everywhere else.
| grecy wrote:
| > _but there are probably reasons it hasn't already changed
| everywhere else_
|
| Yes, the legacy OEMs are constrained by their suppliers, who
| dictate what they can (not) do.
| hef19898 wrote:
| In automotive, it is usually the other way round.
| Regardless, what exactly was wrong with the existing 12 and
| 24 V systems for auxiliaries that _absolutely_ needed to be
| changed?
| mpreda wrote:
| High current (amperage) requiring thicker wires, or more
| wires, thicker/heavier connections, more expensive
| switches, more cooling etc.
| grecy wrote:
| The move to 48V means much less power is lost (power loss
| = (IxI)xR ), cables can be much smaller, cables and
| terminals can be much lighter and much less copper can be
| used used.
|
| Basically it's just a more efficient way of doing things.
|
| Elon has said it's not a revolution, or ground breaking
| in any way, it is simply a step improvement. Anyone could
| have done it. Tesla did it.
| hef19898 wrote:
| As others pointed out lready, others did it, too.
| grecy wrote:
| Re-read the comments, others have not done it.
|
| Audi has a mild-hybrid 48V (as do many others) that also
| runs some other things like active roll control and the
| power steering pump.
|
| They still have a 12v system running infotainment, seat
| heaters, defrosters, powered seats, lights, etc. etc.
| hef19898 wrote:
| As I never knowingly listen to music on 48V, is it reall
| so much better than 12V?
| kwhitefoot wrote:
| Do Tesla have 800 V batteries yet? I thought they were still
| using 400 V for all the cars.
| crishoj wrote:
| Cybertruck is the first Tesla vehicle with 800v architecture.
| The S3XY lineup uses 400v.
| coffeeblack wrote:
| Musk did an interview with Sandy Munro about it. Worth
| watching.
| cashsterling wrote:
| And FWIW... 24V is very common for DC circuits in industrial
| control systems. 48V is used too but less common; however, 48V
| is very common in telecom.
| merb wrote:
| up till now most ev's used 400v there are some with 800v and
| more premium models do get 800v
| jeffparsons wrote:
| I'm ignorant and curious: why 48V specifically? Why not 40V? Why
| not 50V? Is there some ideal ratio that makes DC-DC conversions
| more efficient or something?
|
| For comparison, Makita (and I think some other power tool makers)
| have augmented their 12V lineup with a newer 40V platform for
| tools that need a bit more oomph. I guess there's no need for
| them to interoperate with other DC voltages, so maybe that
| explains the "messy" number?
|
| USB, on the other hand, recently grew support for a handful of
| pleasantly neat voltages:
|
| > Increased power levels from existing USB standards up to 240W.
| New 28V, 36V, and 48V fixed voltages enable up to 140W, 180W and
| 240W power levels, respectively.
|
| Does anybody know how these decisions are made?
| owengee wrote:
| For batteries it tends to be multiple of the battery cell
| voltages. So 48v is probably so you could wire 4x12v batteries
| in series but that is a guess. With tool voltages this tends to
| be a multiple of the nominal battery voltage (rounded for
| marketing).
| stickfigure wrote:
| To riff on this, a lead-acid cell is 2.2v. If you look at the
| 12v battery in your (typical) car, it has six cells. It's
| less obvious with modern sealed batteries, but super obvious
| with flooded lead acid batteries in golf carts.
|
| Lithium batteries do not have 2.2v cells; typical li-ion
| cells are 3.7v. So there's no particular reason why you
| should stack them to 48v, _except_ that there 's already some
| amount of industrial capacity for 48v components due to the
| preponderance of 48v golf carts.
|
| Of course, these systems don't work at _exactly_ 12v or 48v
| or whatever; voltage on the bus fluctuates with state of
| charge (and state of charging).
| 1970-01-01 wrote:
| This is it, there are many ways to get there. The 48-volt
| architecture is achievable with four 12-volt lead acid
| batteries in series, or thirteen lithium-ion cells in
| series at their nominal 3.7-volts, or fifteen LiFePo4 cells
| in series at their nominal 3.2 volts. You can ask for any
| of these to manufacture a 48-volt vehicle.
| RadixDLT wrote:
| is tesla forced to do so because the other automakers are
| clueless?
| teo_zero wrote:
| Please note that all benefits listed in TFA for 48V vs 12V are
| valid for 220V vs 110V, too.
| mpreda wrote:
| Could I have 48V for my GPU power supply as well, please?
| singlepaynews wrote:
| Does anyone know where a civilian (me) could access a pdf?
| maxlin wrote:
| Tesla is so cool. Leading not just by example but literally
| giving patents and designs away for free.
| gravitywave wrote:
| Has this document actually been posted anywhere?
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