[HN Gopher] Data centers are transitioning from AC to DC
___________________________________________________________________
Data centers are transitioning from AC to DC
Author : jnord
Score : 295 points
Date : 2026-03-25 00:44 UTC (22 hours ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| shdudns wrote:
| How is DC better than a three phase delta 800Vrms, at 400Hz?
|
| - Three conductors vs two, but they can be the next gauge up
| since the current flows on three conductors
|
| - no significant skin effect at 400Hz -> use speaker wire, lol.
|
| - large voltage/current DC brakers are.. gnarly, and expensive.
| DC does not like to stop flowing
|
| - The 400Hz distribution industry is massive; the entire
| aerospace industry runs on it. No need for niche or custom parts.
|
| - 3 phase @ 400Hz is x6 = 2.4kHz. Six diodes will rectify it with
| almost no relevant amount of ripple (Vmin is 87% of Vmax) and
| very small caps will smooth it.
|
| As an aside, with three (or more) phase you can use multi-tap
| transformers and get an arbitrary number of poles. 7 phases at
| 400Hz -> 5.6kHz. Your PSU is now 14 diodes and a ceramic cap.
|
| - you still get to use step up/down transformers, but at 400Hz
| they're very small.
|
| - merging power sources is a lot easier (but for the phase angle)
|
| - DC-DC converters are great, but you're not going to beat a
| transformer in efficiency or reliability
| shiroiuma wrote:
| >- no significant skin effect at 400Hz -> use speaker wire,
| lol.
|
| What are you talking about? There's a very significant skin
| effect at 400Hz. Skin effect goes up with frequency. These
| datacenters use copper busbars, not cable, so skin effect is an
| important consideration.
| shdudns wrote:
| At 100 000 A for a 100 MW data center at 1000 V, speaker wire
| is a joke.
|
| You obviously need at least a dozen stands in parallel!!
|
| Clearly skin effect scales with frequency but, 400 Hz is
| still low, only 2.5x lines frequency (the scale is by the
| root); so the skin depth is 3mm. 3mm on each side makes for a
| pretty hefty rectangular cross-section.
| bigiain wrote:
| If you could get that 100,000Amps flowing through your
| speaker wire, the vaporised copper and the plasma channel
| would probably keep your 100MW flowing, at least until your
| building caught fire.
| jacquesm wrote:
| Even your monster cable? ;)
| bigiain wrote:
| Well, it'd still vaporise, but it'd sound smoother and
| more musical as it did it, and the soundstage from the
| plasma arc would be _stunning!_
| jacquesm wrote:
| It's almost worth the experiment and your cables are a
| sacrifice I'm willing to make. For science, of course.
| bigiain wrote:
| You're _so_ right!
|
| I'm pretty sure you have my delivery address from when I
| bought sorted Lego from you about 10 years back.
|
| Let me know when to expect the 100,000Amp test equipment!
|
| I shall make sure I wear better PPE than just my reading
| glasses.
|
| :-)
| jacquesm wrote:
| This would be the funniest thing to do. 100K Amps is
| doable, the question is for how long. That would be one
| very impressive bank of capacitors. And to turn a 00 into
| plasma would have some spectacular side effects, such as
| raining molten copper across a sizeable area. Just your
| reading glasses would indeed not be enough, there
| probably isn't any PPE that I would consider entirely
| safe other than sufficient distance from ground zero. But
| now I'm really curious. I have a spot welder that will do
| bursts of 5KA and that will happily throw the breaker
| every so many welds. 100KA sustained will be a fair
| engineering challenge.
|
| Ah, that lego project... that was one I always wondered
| if I should have industrialized it but sourcing enough
| lego was a real problem.
| adiabatichottub wrote:
| Ho ho ho, you asked for it:
|
| https://www.youtube.com/watch?v=OC7sNfNuTNU
| bigiain wrote:
| See also (as posted elsethread):
| https://www.youtube.com/watch?v=RoGbrgOhPes
| jacquesm wrote:
| Holy crap. That's a whole series of bad ideas extremely
| well executed. That guy probably has never seen what a
| lead acid battery can do when it explodes. He keeps
| hiding away from the hot metal but in the path of ~half
| of those batteries. Ignorance is bliss.
|
| That's low voltage lightning :)
| adiabatichottub wrote:
| He was gifted an arch flash suit by the guys from
| Lightening on Demand :D
| jacquesm wrote:
| "The gift of life". Complete madness.
| adamking wrote:
| > no significant skin effect at 400Hz -> use speaker wire, lol
|
| now run that unshielded wire 50 meters past racks of GPUs and
| enjoy your EMI
|
| > The 400Hz distribution industry is massive; the entire
| aerospace industry runs on it
|
| nothing in that catalog is rated for 100kW-1MW rack loads at
| 800Vrms
|
| > 3 phase @ 400Hz is x6 = 2.4kHz... Your PSU is now 14 diodes
| and a ceramic cap
|
| you still need an inverter-based UPS upstream, which is the
| exact conversion stage DC eliminates
|
| > large voltage/current DC breakers are.. gnarly, and
| expensive. DC does not like to stop flowing
|
| SiC solid-state DC breakers are shipping today from every major
| vendor
|
| > DC-DC converters are great, but you're not going to beat a
| transformer in efficiency or reliability
|
| wide-bandgap converters are at 95%+ with no moving parts
| shdudns wrote:
| "now run that unshielded wire 50 meters past racks of GPUs
| and enjoy your EMI"
|
| Multipole expansion scales faster than r^2.
|
| Also, im not in the field (clearly) but GPUs cant handle 2.4
| kHz? The quarter wavelength is 30km.
|
| "nothing in that catalog is rated for 100kW-1MW rack loads at
| 800Vrms"
|
| Current wise, the catalog covers this track just fine. As to
| the voltages, well that's the whole point of AC! The voltage
| you need is but a few loops of wire away.
|
| "you still need an inverter-based UPS upstream, which is the
| exact conversion stage DC eliminates"
|
| So keep it? To clarify, this is the "we're too good for
| plebeian power, so we'll transform it AC->DC->AC", right?
|
| "SiC solid-state DC breakers are shipping today from every
| major vendor"
|
| Of course they do. They're also pricey, have limited current
| capability (both capital costs and therefore irrelevant when
| the industry is awash with GCC money) and lower conduction,
| and therefore higher heat.
|
| They're really nice though.
|
| "wide-bandgap converters are at 95%+ with no moving parts"
|
| transformers have no moving parts. Loaded they can do 97%+
| efficiency, or 2MW of heat eliminated on a 100MW center.
| prezk wrote:
| An advanced AI rack might use 100kW = 800V 125A, requiring
| gauge 2, quarter inch diameter---this isn't your lol speaker
| wire. Actually, I apologize, I realized I may be talking to a
| serious audiophile, didn't mean to disrespect your Monster
| cables.
|
| The skin depth by the way is sqrt(2 1.7e-8 ohm m / (2 pi 400Hz
| mu0))=~3mm for copper---OK for single rack, but starts to be
| significant for the type of bus bars that an aisle of racks
| might want.
|
| As for efficiency, both 400Hz transformers AND fancy DC-DC
| converters are around 95% efficient, except that AC requires
| electronics to rectify it to DC, losing another few percent, so
| the slight advantage goes to DC, actually.
|
| As for merging power, remember that DC DC converter uses an
| internal AC stage, so it's the same---you can have multiple
| primary windings, just like for plain AC.
| bigiain wrote:
| > I realized I may be talking to a serious audiophile, didn't
| mean to disrespect your Monster cables.
|
| I am a recovering audiophool.
|
| I do own a pair of 2m long Monster Cable speaker cables (with
| locking gold plated banana plugs). I am fairly certain I've
| used welders with smaller cables.
|
| (In my defence, I bought those as a teenager in the late 80s.
| I am not so easily marketed to with snake oil these days. I
| hope.)
|
| (On the other hand, I really like the idea of a reliably
| stable plus and minus 70V or maybe 100V DC power supply to my
| house. That'd make audio power amplifiers much easier and
| lighter...)
| hrmtst93837 wrote:
| 400Hz is an aircraft hack. In a data center, where batteries
| and most of the stuff behind the PSU already want DC, cutting
| conversion stages and a bunch of UPS weirdness is a boring win
| even if DC breakers are nastier and pricier. If you want
| switchgear with aerospace pricing in a building full of racks,
| AC at boutique frequencies is one way to get there.
| bandrami wrote:
| I stg if I see the kids talk about Westinghouse being
| batterymogged I'm leaving the Internet
| otterley wrote:
| DC power has been an option for datacenter equipment since I was
| a young lad racking and stacking hardware. Cisco, Dell, HPE, IBM,
| and countless others all had DC supply options. Same with PDUs.
| What's old is new again.
|
| See e.g. https://www.dell.com/support/kbdoc/en-
| us/000221234/wiring-in...
| bluGill wrote:
| 48vdc was common in phone exchanges. They filled the basement
| with lead-acid batteries and to could run without the grid for
| a couple weeks. In turn the phone was 99.999% reliable for
| decades.
| mjuarez wrote:
| Not to be _that_ guy, but it was technically -48V DC.
|
| Honestly, that was pretty surprising to me when I had to work
| with some telco equipment a couple of decades ago. To this
| day, I don't think I've encountered anything else that
| requires negative voltage relative to ground.
| yostrovs wrote:
| Check out older English cars.
| bluGill wrote:
| positive ground used to be in all cars. When they went from
| 6 volts to 12 the disadvantages became appearant fast and
| so everyone went negative ground then (mid 1950s). I am not
| clear why positive ground was bad (maybe corrosion?)
| servo_sausage wrote:
| Is that something other than a labelling convention? Is
| ground actually connected to a earth stake?
| CamperBob2 wrote:
| Cathodic protection against corrosion was the goal of
| using -48V, in the telcos' case.
| myself248 wrote:
| And the telegraph lines before that.
| jacquesm wrote:
| Yes, and that tiny little difference can cost you a lot of
| expensive gear if you run it off the battery and plug in a
| serial port or something like that. You'll also learn first
| hand what arc welding looks like without welding glass.
| SAI_Peregrinus wrote:
| Lots of amplifier circuits need a bipolar supply: both
| positive and negative voltages with respect to ground.
| aidenn0 wrote:
| RTL and DTL both needed negative-voltage relative to
| ground, as do many analog circuits.
| em3rgent0rdr wrote:
| Some old guitar effects used -9V DC.[1] And the convention
| with guitar effects power adapter is the barrel is center
| negative (which is motivated with facilitating easy wiring
| of the socket's switch to connect to a 9V battery inside).
|
| [1] https://www.analogisnotdead.com/article26/what-is-
| going-on-w...
| HWR_14 wrote:
| Can you explain why it's -48 VDC as opposed to 48 VDC with
| the + and - inputs mislabeled?
| jojobas wrote:
| In short, ground.
| crote wrote:
| Because the chassis is connected to ground (as in, a
| literal grounding rod hammered into the soil) and by
| definition your 0V reference point.
|
| The crucial difference is the direction in which the
| current is flowing: is it going "in to", or "out of" a
| hot wire? This becomes rather important when those wires
| are leaving the building and are buried underground for
| miles, where they will _inevitably_ develop minor faults.
|
| With +48V corrosion will attack all those individual
| telephone wires, which will rapidly become a huge
| maintenance nightmare as you have to chase the precise
| location of each, dig it up, and patch it.
|
| With -48V corrosion will attack the grounding rod at your
| exchange. Still not ideal, but monitoring it isn't too
| bad and replacing a corroded grounding rod isn't that
| difficult. Telephone wires will still develop minor
| faults, but it'll just cause some additional load rather
| than inevitably corroding away.
| tinyhitman wrote:
| Do you also happen to why this is not more common? Must
| be useful for more than just telephone wires.
| bluGill wrote:
| Most large scale systems are AC because transformers are
| relatively cheap, low maintenance, and efficient. When
| the system is AC ground makes no difference.
|
| With DC systems you generally think about the issues -
| which is why modern cars are negative ground. However
| other than cars most people never encounter power systems
| of any size - inside a computer the voltages and
| distances are usually small enough that it doesn't matter
| what ground is. Not to mention most computers don't even
| have a chassis ground plane (there are circuit board
| ground planes but they conceptually different), and with
| non-conductive (plastic) cases ground doesn't even make
| sense.
| jcalvinowens wrote:
| > When the system is AC ground makes no difference.
|
| With AC it's about where the ground is attached along the
| length of the transformer secondary. In the EU they
| ground one of the ends of the secondary, in the US we
| ground the center point.
|
| I don't get to say this very often ... but the US way is
| objectively safer with no downside: 99% of human shocks
| are via ground, and it halves the voltage to ground (120V
| vs 240V). A neutral isn't required if there aren't 120V
| loads.
| Liftyee wrote:
| I agree that the US _voltage_ is safer (with the tradeoff
| of lower output powers available at your outlets).
| However, I suspect this is more than negated by the US
| plug design, which carries a much larger risk of shocks
| than almost all EU plug designs (Schuko, British /Type G,
| etc...)
|
| - uninsulated metal pins make contact with supply while
| partially exposed - much smaller distance between metal
| pins and the edge of the plug
| jcalvinowens wrote:
| 100% agree the US plug designs are terrible.
|
| But there's no inherent power tradeoff: you can have 240V
| outlets in the US, with the two prongs both 120V to
| ground. They're just really uncommon in residences.
| bluGill wrote:
| Dryers and Stoves/range outlets are very common in US
| houses. Of course they are generally hidden behind the
| device and so most people are not sure if they have them
| at not. They are also reasonably common in garages
| (welders, air compressors, table saws... - if your hobby
| needs them you install them, otherwise you won't have
| them).
| crote wrote:
| In the EU it is quite common for houses to have three-
| phase power. If you squint a bit, the grounded neutral of
| the Y transformer isn't entirely unlike the grounded
| center tap in the US. The voltage is a lot higher, of
| course!
| Dylan16807 wrote:
| > If you squint a bit, the grounded neutral of the Y
| transformer isn't entirely unlike the grounded center tap
| in the US.
|
| Yes, but you only get the safety benefit on three phase
| equipment.
|
| In the US there aren't a lot of 240V plugs, but if you
| get some installed you can get the safety benefits with
| plain old consumer goods.
| crote wrote:
| It is! Look up "impressed current cathodic protection":
| you apply a small DC voltage to, say, pipelines to
| prevent corrosion.
| nhecker wrote:
| I ran into a guy at a hardware store who ran just such a
| power supply attached our city's water (or was it natural
| gas?) infrastructure. I was incredulous, but the idea
| that it helped prevent corrosion did make sense.
| HWR_14 wrote:
| So, there is a true value for 0?
|
| Does that mean when you have electronics and use multiple
| dc-dc converters all the inputs and outputs share the
| same ground, it's not just the values for that pair of
| wires?
|
| And if I want to use a telephone on an incorrectly wired
| 48dc circuit, I could switch the positive and negative
| wires, as long as the circuit in the telephone is
| isolated and never touches ground?
|
| Thanks. Somehow I got in my head that all circuits were
| just about the delta from neutral and therefore nothing
| outside them mattered.
| wat10000 wrote:
| There is a true zero potential. You can detect this
| because two charged objects with zero delta between them
| will still repel each other.
|
| I think a circuit should mostly care about the deltas,
| but when you're talking about things like phone lines,
| the earth becomes part of your circuit. You can't
| influence its potential (it's almost exactly neutral
| because any charge imbalance gets removed by interaction
| with the interplanetary medium) so everything else is
| going to end up being determined by what you need for
| their relative potential to that.
| bonzini wrote:
| > all the inputs and outputs share the same ground, it's
| not just the values for that pair of wires?
|
| No, it depends on the converter. There are converters
| that leave 160V on the DC power rail for a 110V AC input,
| and 155V on the DC "ground" rail.
|
| They are economic and you could find then when galvanic
| isolation is at least in theory not important, but
| they're terribly unsafe when used on PCBs that people
| might muck with.
|
| If you have some "normal" converters and some of this
| kind, sharing the ground would be quite dangerous.
| fecal_henge wrote:
| I am STILL designing hardware for -48v telco standard. The
| first thing we do is convert -48 -> 48v. That's 4 square
| inches of PCB space we waste.
| eqvinox wrote:
| What do you need +48V for?
| pluies wrote:
| Well if it's negative 48V the electricty flows out of
| your circuit and back to the grid, so you need to make it
| positive to have the electricity come in.
| djmips wrote:
| Likely as a basis for converting to other useful DC
| voltages.
| fecal_henge wrote:
| We go -48 -> 48 -> 12 -> 3v3,1v8 etc etc. If you went 48
| straight to POL voltages then you would have horrific
| converter performance.
| eqvinox wrote:
| > If you went 48 straight to POL voltages then you would
| have horrific converter performance.
|
| What's horrific converter performance in numbers?
|
| An isolated flyback (to 12V) should be able to hit >92%
| and doesn't care if it's fed -48V or +48V or +-24V. TI
| webench gives me 95% though I'd only believe that if I'd
| built and measured it. What's the performance of your
| -48V - +48V?
|
| [with the caveat that these frequently require custom
| transformers... not an issue with large runs, but finding
| something that can be done with an existing part for
| smaller runs is... meh]
| fecal_henge wrote:
| -48 to 48 claims something like 97% (load dependent of
| course). It also needs to arbitrate between two input
| supplies for glitchless redundancy, plus have PM bus and
| other spec mandated stuff. There is no technical reason
| why you cant go -48 -> 12 as you state with good
| efficiceny, but we cant get hold of a part that ticks all
| the boxes.
|
| Horrific performance by my definition would be 48v to say
| 1v. We only realistically use buck topologies for POL
| supplies. Such a ratio is really bad for current
| transients, not to mention issues like minimum on times
| for the controller.
| eqvinox wrote:
| I'm just surprised that either input isolation isn't on
| your spec, or it still somehow works out better with
| isolated to +48V than straight to 12V... but I guess if
| your spec requires other things, it makes sense.
|
| (Thanks for the info!)
| swed420 wrote:
| > I don't think I've encountered anything else that
| requires negative voltage relative to ground
|
| Automotive collectors can probably still relate to cars
| from the 1920s-50s having a "positive ground."
| fuzzfactor wrote:
| With positive ground the traditional more-sacrificial
| spark plugs lasted longer.
| divbzero wrote:
| Interesting, so this is why the phone line still worked when
| power was out across the whole town.
| eqvinox wrote:
| Yeah, it used to be that you could still make calls
| (particularly to emergency services) even in complete power
| outages, for as long as your local exchange has batteries
| for. (AFAIR that tended to be on the order of hours, but
| probably differs quite a bit across locations and
| regulatory domains/countries.)
|
| Another thing we lost in the age of VoIP landlines, but
| then again mobile towers also have batteries. Just don't be
| unlucky and have a power outage with 3% battery on your
| phone...
| MathMonkeyMan wrote:
| Yeah I always heard that the phone lines carried their own
| power, and in Florida the phones did keep working when the
| power went out, but I never knew why.
|
| So the grid was always charging up the lead acid batteries,
| and the phone lines were always draining them? Or was there
| some kind of power switching going on where when the grid was
| available the batteries would just get "topped off"
| occasionally and were only drained when the power went out?
| bluGill wrote:
| Grid charging batteries, phone draining them as I
| understand. Of course there were switches all over the us
| so I can't make blanket claims but from what I hear that
| was normal.
| pocksuppet wrote:
| The phone grid predated the electrical grid. There was no
| other choice for power.
|
| Actually, there was one. Even earlier phones had their own
| power. A dry-cell battery in each phone, and every 6
| months, the phone company would come around with a cart and
| replace everyone's battery. Central battery was found to be
| more convenient, since phone company employees didn't have
| to go around to everyone's site. Central offices could
| economize scale and have actual generators feeding
| rechargeable batteries.
| qingcharles wrote:
| It's a pretty decent chunk of power down a POTS cable too,
| as it was designed to ring multiple big chunky metal bells
| in the days of yore.
|
| I was wiring in a phone extension for my grandma once as a
| boy and grabbed the live cable instead of the extension and
| stripped the wire with my teeth (as you do). I've been
| electrocuted a great number of times by the mains AC, but
| getting hit by that juicy DC was the best one yet. Jumped
| me 6ft across the room :D
| rdtsc wrote:
| The teeth. Yikes! But yeah, I remember having the rotary
| phone disassembled and touching the wires adjusting
| something when a ring came. Gave me enough of a jolt to
| remember.
| elcritch wrote:
| I discovered the same exact thing wiring a second phone
| line to my bedroom as a teenager. I jumped into a pile of
| fiberglass insulation! :/
| SigmundA wrote:
| The batteries and phone lines were one system at -48v with
| power supplies converting AC power to DC while grid /
| generator is up.
|
| The batteries are floated at the line voltage nothing was
| really charging or discharging and there was no switchover.
|
| This is similar to your cars 12v dc power system such the
| when the car is running the alternator is providing DC
| power and the batteries float doing nothing except
| buffering large fluctuations stabilizing voltage.
| idiotsecant wrote:
| I still have a bunch of 48vdc comms gear in my powerplant.
| beAbU wrote:
| Why do you have a powerplant?
| bluGill wrote:
| Power plant is the convention for any large company that
| has backup power. A few UPSes for the server room - they
| are the power plant. A backup generator - power plant.
| Sometimes even just the room with all the break boxes
| from where the grid comes in is called the power plant
| (though normally power plant is reserved for backup
| power). It is extremely common for commercial buildings
| to have their own power plant. Most of their power comes
| from the grid in all cases, but they have a power plant.
| At commercial scale you can often save money by buying a
| backup generator powerful enough for your whole building
| so you disconnect from the grid when grid power is in
| highest demand (see your utility, then your accountant:
| for details if you can afford a generator this large)
| tverbeure wrote:
| -48V! :-)
| boricj wrote:
| I'm working on stuff in that market, it's still largely is.
| _DC Power System Design For Telecommunications_ is still a
| must read and it doesn 't even cover the last 15 years or so
| of development, notably lithium batteries and high efficiency
| rectifiers.
|
| I will say that this is a surprisingly deep and complex
| domain. The amount of flexibility, variety and scalability
| you see in DC architectures is mind-boogling. They can span
| from a 3kW system that fits in 2U all the way to multiples of
| 100kWs that span entire buildings and be powered through any
| combination of grid, solar and/or gas.
| amelius wrote:
| You need thick cables if you want to power a rack with 48V.
| superxpro12 wrote:
| This reminds me of the early google data centers that
| directly soldered those massive duracell lantern batteries
| directly to the motherboards as a primitive battery backup.
| I'm struggling to google examples of it, this would have been
| back around 2008, but i have a vivid memory of it.
|
| edit: found it https://www.cnet.com/tech/tech-
| industry/google-uncloaks-once...
| _fizz_buzz_ wrote:
| Obviously 48VDC has been around and internally they will
| probably still step down to 48V. But these 48V islands are
| nowadays inter connected by regular AC grid. They want to
| replace that interconnection with a 800VDc bus. I kind of
| assume they chose 800vdc because there are already bunch of
| stuff available from EVs which also have 800vdc battery packs
| now.
| 15155 wrote:
| They chose 800VDC because it's a convenient multiple that is
| the peak possible with a two-level 650V (probably GaN) FET
| arrangement.
| eternauta3k wrote:
| And why is 650V special?
| 15155 wrote:
| Historical, physical, engineering reasons.
|
| Much of the world's mains-voltage electronics run at 240V
| (historical) and have PFC circuits (which are essentially
| just boost converters) that run at ~400V DC link
| voltages. 650V gives you enough headroom to tolerate
| overshoots and still have an 80% safety margin with a
| single level topology.
|
| This voltage also coincidentally is a convenient
| crossover point where silicon MOSFETs start to become
| inefficient and GaN FETs have recently become feasible
| and mass-produced.
| _zoltan_ wrote:
| 800V DC is definitely not "old".
| stego-tech wrote:
| I've been hearing this line for over a decade, now. "Immersion
| cooling will make data centers scale!" "Converting to DC at the
| perimeter increases density!"
|
| Yes, of course both of those things are true, and yes, some data
| centers do engage in those processes for their unique advantages.
| The issue is that aside from specialty kit designed for that use
| (like the AWS Outposts with their DC conversion), the rank-and-
| file kit is still predominantly AC-driven, and that doesn't seem
| to be changing just yet.
|
| While I'd love to see more DC-flavored kit accessible to the
| mainstream, it's a chicken-and-egg problem that neither the power
| vendors (APC, Eaton, etc) or the kit makers (Dell, Cisco, HP,
| Supermicro, etc) seem to want to take the plunge on first. Until
| then, this remains a niche-feature for niche-users deal, I wager.
| otterley wrote:
| Those vendors all have DC power supply options, to my
| knowledge. It's hardly new; early telco datacenters had DC
| power rails, since Western Electric switching equipment ran on
| 48VDC.
|
| https://www.nokia.com/bell-labs/publications-and-media/publi...
| stego-tech wrote:
| That's just it though, telco DCs != Compute DCs. Telcos had a
| vested interest in DC adoption because their wireline
| networks used it anyway, and the fewer conversions being done
| the more efficient their deployments were.
|
| Every single DC I've worked in, from two racks to hundreds,
| has been AC-driven. It's just cheaper to go after
| inefficiencies in consumption first with standard kit than to
| optimize for AC-DC conversion loss. I'm not saying DC isn't
| the future so much as I've been hearing it's the future for
| about as long as Elmo's promised FSD is coming "next year".
| jacquesm wrote:
| I think the real reason is because battery power didn't
| have to be converted twice to be able to run the gear in
| case of an outage, so you'd get longer runtime in case of a
| power failure, and it saves a bunch of money on supplies
| and inverters because you effectively only need a single
| giant supply for all of the gear and those tend to be more
| efficient (and easier to keep cool) than a whole raft of
| smaller ones.
| arijun wrote:
| Surely if it makes sense for the big players, they will do it,
| and then the benefits will trickle down to the rest? Like how
| Formula 1 technology will end up in consumer vehicles.
| gizmo686 wrote:
| At least for servers, power supplies are highly modular. It
| just takes 1 moderately sized customer to commit to buying
| them, and a DC module will appear.
|
| Looking at the manual for the first server line that came to
| mind, you can buy a Dell PowerEdge R730 today with a first
| party support DC power supply.
| dist-epoch wrote:
| These are GigaWatt data centers. For a single one they buy
| equipment by the container ship. Nothing is niche about it.
| crote wrote:
| As seen on HN a few days ago, immersion cooling is dead: turns
| out the risks of getting sued to oblivion due to widespread
| PFAS contamination isn't worth it. [0]
|
| DC doesn't have such a killer. There are a decent bunch of
| benefits, and the main drawback is gear availability. However,
| the chicken-and-egg problem is being solved by hyperscalers.
| Like it or not, the rank-and-file of small & medium businesses
| is _dying_ , and massive deployments like AWS/GCP/Azure/Meta
| are becoming the norm. Those four already account for 44% of
| data center capacity! If they switch to DC can you still call
| it "specialty kit", or would it perhaps be more accurate to
| call it "industry norm"?
|
| It is becoming increasingly obvious that the rest of the
| industry is essentially getting Big Tech's leftovers. I
| wouldn't be surprised if DC became the norm for colocation over
| the next few decades.
|
| [0]: https://thecoolingreport.com/intel/pfas-two-phase-
| immersion-...
| mrguyorama wrote:
| They poison water supplies, knowingly, for decades, and it
| only takes $12 billion dollars to finally get them to stop?
|
| Fucks sake.
| KaiserPro wrote:
| Immersion cooling was/is so fucking impractical it is only
| useful for very specific issues. If you talk to any engineer
| who worked on CRAY machines that were full of liquid freon,
| they'll tell how hard it is to do quick swaps of anything.
|
| Its much cheaper, quicker and easier to use cooling blocks with
| leak proof quick connectors to do liquid cooling. It means you
| can use normal equipment, and don't need to re-re-enforce the
| floor.
|
| A lot of "edge" stuff has 12/48v screw terminals, which I
| suspect is because they are designed to be telco compatible.
|
| For megawatt racks though, I'm still not really sure.
| kjs3 wrote:
| We had a cluster of liquid cooled CDC Cyber mainframes. One
| of them developed a bad leak and managed to drain itself into
| the raised floor. This was a Very Bad Day for many folks in
| the computer center.
|
| Edit: s/have/had/
| jeffbee wrote:
| It is weird to me how far from the state of the art mainstream
| server equipment is. I can't imagine anything worse than AC-AC
| UPS, active PDUs, and redundant AC-DC supplies in each rack
| unit, but that's still how people are doing it.
| _zoltan_ wrote:
| I recommend reading these two:
|
| https://developer.nvidia.com/blog/nvidia-800-v-hvdc-architec...
|
| https://blogs.nvidia.com/blog/gigawatt-ai-factories-ocp-vera...
|
| almost everybody in the industry is embracing 800V DC mostly
| because of Vera Rubin and the increased electricity
| requirements.
| hristov wrote:
| It is absolutely stupid to talk about this as edisons revenge. If
| Tesla had the modern high power transistors needed to get high
| voltage dc out of the ac produced from a spinning turbine he
| would be all for high voltage dc too. Tesla understood that high
| voltage was needed for efficient long range transmission. He also
| understood that transformers were the inly remotely efficient way
| to climb up to and down from these high voltages. And
| transformers only work with ac. So he designed an ac system and
| even designed some better transformers for it.
|
| If there was anything like a high power transistor back then he
| would have used that. High power transistors that are robust
| enough to handle the grid were designed inly recently over 100
| years after the tesla/edison ac/dc argument.
| arijun wrote:
| Also, if anything would have been Edison's revenge it would
| have been HVDC, where they're sending power long distances with
| DC. (But as you said, even there it wouldn't make a ton of
| sense, since they were arguing in a different era).
| themafia wrote:
| The two primary reasons to do that are to allow the intertie
| of two AC grids that are not otherwise synchronized, and to
| take advantage of "earth return" paths when necessary to
| double the capacity of the line. The latter you may need to
| consider just to make the line cost effective over an
| equivalent AC span.
| bluGill wrote:
| Tesla also design the modern induction motor which needs ac.
| Though these days we often run them on a phase generator which
| has a dc step.
| jacquesm wrote:
| Agreed, for the IEEE to go down this route is more than a
| little weird.
| Georgelemental wrote:
| It's just a fun title, you are overthinking it
| chrneu wrote:
| the internet really needs to stfu about tesla and get over that
| oatmeal comic that spawned a billion internet myths. dude was a
| decent inventor but suffered from chronic mental health issues
| and, in his lifetime, wasted so much time/energy/money and
| burned so many bridges with his horrible attitude. there's a
| reason most people didnt like him in his day, he was a
| depressed asshole who alienated everyone around him, and yes I
| know he was likely gay in a time when that wasn't cool. the
| fact still remains; his inventions are massively overblown by
| internet nerds.
|
| the podcaster Sebastian Major from "Our Fake History" did a
| looonnngg patreon episode on tesla and debunked most of the
| weird myths around tesla. Sebastian doesn't have a vendetta or
| anything, it's just amazing how much of the Tesla stuff is just
| nonsense or is viewed through a very weird bias nowadays. Major
| also briefly touches on the weird Edison stuff and how the
| internet has twisted Edison into a villain.
| anonymousiam wrote:
| Tesla was an outstanding technologist, but a poor
| businessman. He had a "vision" (actually more than one) about
| how his ideas could transform the world. Some of his ideas
| were amazing, but he was swindled out of his patents because
| the investors knew he had a passion and wanted to see them in
| use. The polyphase AC motor or fluorescent light bulb could
| have made him millions.
|
| IMHO, the vision he had about universal free electricity
| (transmitted wirelessly) was the dumbest. It was a novel
| idea, and he invested a lot (his time and other people's
| money) in it. The problem with his idea is that there was no
| way to monetize it (and profit from it). (There were also the
| technical issues of the power loss over distance (1/R^2), the
| harm to the environment, and the interference with radio
| communications.)
|
| Edison was quite a villain. He stole many of his
| "inventions", and orchestrated a PR campaign against Tesla
| touting the "evils" of AC power. AFAIK, the electric chair
| was either invented or inspired by him.
|
| I know these things because I've read many books on various
| topics related to Tesla, and all of this knowledge predates
| the Internet.
| HWR_14 wrote:
| Edison did not invent the electric chair. When the
| inventors were trying to choose between using AC or DC he
| helped them decide on AC as part of his PR campaign.
| fsh wrote:
| Essentially none of this is true. The war of the currents
| was between Edison and Westinghouse, not Tesla. Tesla's
| downfall was that he turned into a crackpot who rejected
| modern science, such as Maxwell's equations, and started
| defrauding investors. Edison was an outspoken opponent of
| the death penalty, and the electric chair used AC simply
| because it is much more deadly.
| chipster_f00 wrote:
| > The war of the currents was between Edison and
| Westinghouse [...]
|
| Thank you for quashing the gross misinformation. I was
| going to post this, but searched and found your comment.
| `\m/`
|
| (I learned of the "Current War" in the 70's, since the
| Edison Museum was in my "backyard" -- and was a common
| destination of local school field trips.)
| aaronbrethorst wrote:
| We're talking about Nikola Tesla, not Elon Musk, and I don't
| think Musk is gay.
| beAbU wrote:
| I think you need to read the post you are responding to
| again.
| elar_verole wrote:
| People need heroes. It's like the Keanu Reeves or Musk era,
| all the ""badass"" stories about this or that soldier / local
| hero / w/e that are very often overblown and get further and
| further away from the initial facts every time they
| resurface. No hate here, just noticing there is a weird
| visceral need to distill stories to their most essential,
| good vs evil, and the Tesla v Edison thing embodies this
| perfectly I think.
| Imustaskforhelp wrote:
| Keanu Reeves and Nikola Tesla to a degree as well, are
| decent figures.
|
| Aside from all the cult classics Keanu is part of like john
| wick and the matrix, even discounting that, he is a good
| person in it of itself who is genuinely humble and might be
| one of the best persons within hollywood.
|
| What I feel pissed about is that people like Andrew Tate
| and others like them took the concept of Matrix and the
| contributions Keanu did within that movie and tried to
| capitalize on that cult classic decades after in the most
| toxic form that might be the issue if we are talking about
| an era
|
| To be honest, Nikola tesla is also a great person within
| the context of his time. GGP's comment is still true but
| Tesla's contributions can hardly be reinstated and I'd much
| rather people believe these to be the heros (Keanu/Tesla)
| rather than Tate/Musk etc.
|
| If I take anything from Keanu, I would like to take his
| humility/humbleness.
| giancarlostoro wrote:
| Tate is just attention hungry. It's pretty obvious. If
| you feed no attention to him, he will go back to where he
| crawled from.
| ndsipa_pomu wrote:
| Whilst I agree that Keanu is a most excellent human, he
| was hardly responsible for the concept of the Matrix. In
| my opinion, Philip K Dick was a major influence (I'm a
| fan and consider him the prophet of the modern age),
| though Gibson's Neuromancer was likely a big influence
| too. (Also, there's the old Doctor Who episode "The
| Deadly Assassin" which features the Matrix).
|
| It always seems to me that the far right are bereft of
| original ideas and always co-opt other pre-existing
| concepts. There's exceptions, but I always find that
| right wing works are always lacking humour or irony (c.f.
| Ayn Rand's works).
| something765478 wrote:
| > the far right are bereft of original ideas and always
| co-opt other pre-existing concepts.
|
| That's not unique to them: Good artists copy; great
| artists steal.
| ndsipa_pomu wrote:
| Yes, but I'd have difficulty in pronouncing Andrew Tate
| as a good or great artist. Maybe con-artist would be the
| highest that I'd go.
| tomtomtom777 wrote:
| "It is only the unimaginative who ever invents. The true
| artist is known by the use he makes of what he annexes.
| And he annexes everything."
|
| - Oscar Wilde
| ngvrnd wrote:
| Except for Keith Moon. All the stories about him are true
| and if anything underplay the truth. :-)
| boomskats wrote:
| I mean yeah, but it's not like the guy's 'horrible attitude'
| came from nowhere. He naiively romanticised migrating to the
| US thinking the game was about scientific progress rather
| than capital, and so he got repeatedly screwed over by almost
| everyone around him for decades.
|
| If I was in his position I'm not sure I'd have taken it as
| well as he did.
| wil421 wrote:
| There's no way he suddenly developed autism or whatever
| mental illness plagued him upon arrival to American. Like
| most absolute geniuses he struggled in other areas. He said
| he had visions as a child.
| balamatom wrote:
| But there is: his neurotype _suddenly_ became
| _considered_ "whatever mental illness" upon arrival in
| Eugenicsland.
| KaiserPro wrote:
| > he was a depressed asshole who alienated everyone around
| him,
|
| enough Edison bashing!
|
| Look, Tesla was a weirdo, but, he was a very good inventor
| who actually invented shit.
|
| Edison was an industrialist, who knew the price of
| everything, and wasn't above spending a lot of money to
| destroy a rival.
|
| Do I idolise Tesla? no, but I respect his understanding of
| high frequency electronics with _really_ primitive tooling.
|
| Do I despise Edison? also no, but he is a massive prick.
| Excellent buisness man, but an abrasive prick never the less.
| throw4847285 wrote:
| Software engineers idolize Tesla because they see themselves
| as the Tesla (a selfless devotee of the abstract idea of
| technology) against evil Edisons (businessmen who only care
| about money and steal other people's ideas). They've
| basically projected the Jobs/Woz divide back onto two
| historical figures who, in reality, barely interacted.
|
| The funniest part is that The Oatmeal comic didn't invent
| this concept, but drew on pre-Internet narratives put forward
| by The Tesla Society, who were mailing busts of Tesla to
| universities around the country since the 70s at least. And
| that organization is explicitly nationalistic and religious,
| tied to other Serbian-American heritage organizations, and
| doing events with the Orthodox church.
| balamatom wrote:
| > And that organization is explicitly nationalistic and
| religious
|
| So are many Serbs (more so if emigrants from atheist-
| socialist Yugoslavia, or descendants of folks who moved
| before WW2) as well as many other nations and organizations
| (America itself lol). So are many Something-Or-Other-
| American individuals and communities.
|
| I presume that the organization(s) sending Tesla busts,
| being American-rooted, have had no illusions about which
| matters will forever remain impossible to communicate to
| Americans. (Such as anything not reducible to paperclip
| optimization.)
|
| Instead, I consider it more likely that the point of
| promoting Tesla was not to impress anyone in America, but
| to uplift Serbia and generally the South Slavs of the
| Balkans _who 'd only gained national sovereignty in Tesla's
| day_: "look, our heritage has already produced an honest-
| to-god American inventor half a jebani vek ago, so you guys
| have zero excuse to act as if you're stuck in the middle
| ages - do join the cargo cult of mordorn civilization
| instead, will ya - we got value to extract from ya!"
|
| >They've basically projected the Jobs/Woz divide back onto
| two historical figures who, in reality, barely interacted.
|
| I'd rather say this has been projected _for_ them, but by
| whom is anyone 's guess; not like there's a shadowy cabal
| operating. Besides said Serbian-American heritage promoters
| and whatever their game is, I guess - but here we're not
| talking mid-XX century Serbian diaspora any more, but a
| "culturally nonspecific" audience.
|
| Much safer to call it "a hivemind situation" when nobody
| knows where some idea comes from, and nobody is accountable
| for rebroadcasting it either, since it comes pre-tagged as
| Good and True and Useful and it is wrongthink to doubt
| those. Especially when the idea is so obviously Useful for
| excusing nonaction. ("I can't be bothered to learn the
| first thing about electricity, even the history of why I
| have access to it in the first place - but now that Tesla
| guy I've vaguely heard of, he was the great genius of the
| people! What better reason to Experience a Positive
| Emotion!")
| tibbydudeza wrote:
| Did he also not fall in love with a pigeon ?.
| teleforce wrote:
| >It is absolutely stupid to talk about this as edisons revenge.
| If Tesla had the modern high power transistors needed to get
| high voltage dc out of the ac produced from a spinning turbine
| he would be all for high voltage dc too.
|
| This!
|
| The soon people realized these facts the better. The pervasive
| high rise buildings did not happen before the invention of
| modern cranes.
|
| Exactly twenty years ago I was doing a novel research on GaN
| characterization, and my supervisors made a lot money with
| consulations around the world, and succesfully founded govt
| funded start-up company around the technology. Together with
| SiC, these are the two game changing power devices with
| wideband semiconductor technology that only maturing recently.
|
| Heck, even the Nobel price winning blue LED discovery was only
| made feasible by GaN. Watch the excellent video made by
| Veritasium for this back story [1].
|
| [1] Why It Was Almost Impossible to Make the Blue LED:
|
| https://youtu.be/AF8d72mA41M
| mcbishop wrote:
| I've heard the EV charging has played a big role in the
| maturation of GaN / SiC.
| teleforce wrote:
| Yes, EV and high frequency electronics (microwave, mmWave,
| photonics) that require very fast switching capability.
| UltraSane wrote:
| And military radars love GaN
| jibal wrote:
| https://shrunk.ai/research-journals/f/cranes-skyhooks-and-
| it...
| ta9000 wrote:
| Does that mean when we run out of Ga there are no more LED
| TVs?
| AndrewDucker wrote:
| Why would we run out of Ga?
| mikkupikku wrote:
| There's a component of modern culture that trains and
| expects people to be extremely pessimistic about long
| term human development. It results in situations above,
| where without any further information people just assume
| by default that were going to run out of a thing and are
| on some collision course with not just a disaster, but
| every single conceivable one.
|
| (Gallium is a byproduct of aluminum production. We aren't
| going to run out.)
| threetonesun wrote:
| My understanding of most elements is if we want more it's
| either pretty easy to make from something else we have a
| lot of, or we need to redo the Big Bang, the latter
| being, in my opinion, a bit of a disaster scenario.
| nkrisc wrote:
| Even synthesizing helium is prohibitively expensive.
| Unless you want whatever heavy decay products we have
| from nuclear waste, synthesizing elements at industrial
| scale probably isn't happening.
|
| Unless by "make from something" else you mean extract the
| element from existing chemical compounds found in Earth,
| in which case we're still just using existing deposits on
| Earth.
| bananaflag wrote:
| On the other hand, it is possible to run out of a metal
| when all of it is either somewhere in some device or
| scattered among landfills (i.e. not concentrated in a
| place like a mine).
| nkrisc wrote:
| That's still not running out. It's still there, just more
| effort to get.
| card_zero wrote:
| "At 10 parts per quadrillion, the Earth's oceans would
| hold 15,000 tonnes of gold", says the Wikipedia page on
| gold.
|
| I'm inclined to think we've lost that gold.
| nkrisc wrote:
| Practically speaking, sure. It's obviously not cost-
| effective to extract it. But it's there if someone can
| get it. I don't expect anyone to be extracting gold from
| ocean water, but there are other source of other elements
| that may not be cost-effective now but could be in the
| future or may simply become necessary despite the cost.
| PowerElectronix wrote:
| Effort high enough to consider that material lost to any
| practical purpose like a tv.
| swiftcoder wrote:
| Cost scales with refinement effort, so it just results in
| more expensive TVs. That said, pretty sure we'll have
| drowned the planet in landfilled TVs long before this
| becomes a serious issue
| nkrisc wrote:
| If prices of certain metals were high enough I bet people
| would stop throwing out TVs and dig up old ones from the
| dump.
| margalabargala wrote:
| It's a byproduct of aluminum production.
|
| The earth's crust is 8% aluminum.
|
| We will have bigger problems before hitting this one.
| adrian_b wrote:
| That is true, but gallium is present in the aluminum and
| zinc ores only in minute quantities.
|
| We will not remain without gallium, but it is impossible
| to scale up the gallium production to a higher level than
| provided by the current productions of aluminum and zinc.
|
| So there is a maximum level of gallium that can be used
| per year and it would not be possible to increase the
| production of blue and white LEDs and of power
| transistors above that level.
|
| Fortunately, the amount of gallium used per device is
| very small, so it is not likely that we will hit that
| level soon. A much more serious problem is the associated
| consumption of indium, for which the resources are much
| less.
| ta9000 wrote:
| Thanks for providing a real answer.
| pwndByDeath wrote:
| Its concentrated in a place like a landfill that already
| has access for large vehicles.
| pyrale wrote:
| > On the other hand, it is possible to run out of a metal
| when all of it is either somewhere in some device or
| scattered among landfills
|
| The metal isn't going to disappear, but it won't be
| concentrated enough to be as easily retrievable.
| myrmidon wrote:
| Sidenote: Whenever someone tells you that (vital) reserves
| of some ressource are going to run out soonish (implying
| drastic consequences), you should be _extremely_ skeptical:
|
| Such predictions have an abysmal historic track record,
| because we tend to find workarounds both on the supply side
| (=> previously undiscovered reserves) as well as
| flexibility on the demand side (using substitutes).
|
| This applies historically for oil, lithium, rare earth
| metals and basically everything else.
|
| edit: I'm not saying we're never gonna run out of
| anything-- I'm just saying to not expect sudden,
| cataclysmic shortages in general, but instead steadily
| rising prices and a somewhat smoothish transition to
| alternatives.
| mschuster91 wrote:
| > Such predictions have an abysmal historic track record,
| because we tend to find workarounds both on the supply
| side (=> previously undiscovered reserves) as well as
| flexibility on the demand side (using substitutes).
|
| That's a classic example of the "preparedness paradox"
| [1]. When no one raises the alarm in time or it is being
| ignored, resources can go (effectively) exhausted before
| alternatives can be found, or countries either need to
| pay extraordinary amounts of money or go to war outright
| - this has happened in the past with guano [2], which was
| used for fertilizer and gunpowder production for well
| over a century until the Haber-Bosch ammonia process was
| developed at the start of the 20th century.
|
| And we're actually seeing a repeat of that as well
| happening right now. Economists and scientists have
| sounded the alarm _for decades_ that oil and gas are
| finite resources and that geopolitical tensions may
| impact everyone... no one gave too much of a fuck because
| one could always "drill baby drill", and now look where
| we are - Iran has blasted about 20% of Qatar's LNG
| capacity alone to pieces and blocked off the Strait of
| Hormuz, sending oil prices skyrocketing.
|
| [1] https://en.wikipedia.org/wiki/Preparedness_paradox
|
| [2] https://en.wikipedia.org/wiki/Guano
| myrmidon wrote:
| I don't see the Guano industry as a straight counter-
| example, it even illustrates my point:
|
| If you had made predictions/scenarios in 1850 based on
| Guano deposits running out within a decade or two, you
| would have mispredicted completely, because a lot of the
| industry just transitioned to sodium nitrate (before
| synthetic fertilisers took over). Nowadays media
| landscape would've gladly made such doom-and-gloom
| predictions for global agriculture back then.
|
| I completely agree that quickly depleting reserves often
| indicate non-sustainable pricing for ressources (which is
| obviously bad long term), but that is very different from
| sudden collapse.
| bluGill wrote:
| I've seen articles from the 1880s claiming oil will run
| out by 1890. 140 years latter...
|
| Yes we can run out of oil, but nobody really knows if or
| even when that will happen. Right now I'm guessing we
| won't run out because wind and solar is so much cheaper
| for most purposes everyone is shifting anyway - this will
| take decades to play out.
| reylas wrote:
| I always add "cheap" to the sentence. It seems they are
| always talking about the cheap version of anything. Going
| to run out of water? Or are we running out of the "cheap"
| version of water that does not have to be processed?
| myrmidon wrote:
| This is a valid point: quickly depleting reserves often
| indicate that pricing is not sustainable. Which is bad.
|
| But non-sustainable pricing is very different from
| "cataclysmic collapse", and too many people expect the
| latter for too many things, which is just not realistic
| in my view (and historical precendent makes a strong case
| against that assumption, too).
|
| A society where water prices gradually increases to
| "reverse-osmosis only" (instead of "pump-from-the-ground-
| everywhere") levels is very different from a society
| where water suddenly runs out.
| nancyminusone wrote:
| Except for gaseous hydrogen and helium, and some
| spacecraft, all other atoms remain on the earth and are
| recoverable with enough energy and effort.
| philipkglass wrote:
| One more exception: uranium. It actually splits into
| smaller atoms when it's used as fuel.
| adrian_b wrote:
| Gallium is expensive to extract because it is extremely
| diluted in the environment.
|
| It accompanies in very low quantities aluminum and zinc, so
| it is extracted only in the mines of aluminum or of zinc,
| as a byproduct.
|
| However, the abundance of gallium is similar to that of
| lithium, while gallium is used in smaller amounts, so there
| is no risk to not have enough gallium in the near future.
|
| On the other hand, all semiconductor devices with gallium
| also use some indium. Indium is used in even greater
| quantities in all LCD or OLED displays, to make transparent
| electrodes.
|
| Indium is an extremely rare element in the entire universe,
| comparable with gold, so for indium there is a much greater
| risk that its reserves will become insufficient.
|
| This could be mitigated by extracting such critical
| elements from the dumped electronic devices, but this is
| very expensive, because only small amounts of indium are
| used per device, so very large amounts of garbage would
| have to be processed in order to extract a sizable amount
| of it.
| da02 wrote:
| What are some novel processes or technologies you see
| becoming more important in the next 5-10 years?
| asah wrote:
| > The pervasive high rise buildings did not happen before the
| invention of modern cranes.
|
| yyy! if we're going to wander off-topic :-) then I should
| mention elevators, water pumps, fire suppression including
| fire truck ladders and more! :-)
| bryanrasmussen wrote:
| sure, and also Montezuma didn't actually plan on diarrhea
| ruining people's vacations, but vernacular usage being what it
| is we have the phrase Montezuma's revenge.
|
| I only found Edison in the headline, I didn't find it anywhere
| in the body, nor did I find Tesla. Glancing through the article
| it almost seems like someone tried to make a catchy headline to
| get clicks.
| fsh wrote:
| It was Westinghouse who pushed the AC grid against his rival
| Edison's DC approach. Tesla was a minor figure working for both
| of them for a bit.
| mr_toad wrote:
| > If there was anything like a high power transistor back then
| he would have used that.
|
| Mercury arc rectifiers were used long before his death.
| crote wrote:
| Yes, but a rectifier only _rectifies_. That 's not going to
| give you DC-DC conversion - let alone converting it to a
| _higher_ voltage for long-distance transmission.
| wildzzz wrote:
| DC-DC before the transistor was difficult to do at scale.
| Vibrators and relays existed but were not reliable long
| term.
| amelius wrote:
| But there was an equivalent: a mechanical switch. Or an
| electromechanical relay. Or a spinning wheel with electrical
| contacts.
| ghighi7878 wrote:
| Title is clickbait. Edison is not mentioned anywhere else in
| article. I am okay with it.
| superxpro12 wrote:
| Yeah this isnt an argument. It was far simpler to wrap some
| copper wire around a chunk of metal than it was to fire up a
| mosfet fabrication plant in the 1800's.
|
| You can have the best idea in the world, but if you cant
| manufacture it you're SOL.
| crimshawz wrote:
| Agree, clickbait.
| metalliqaz wrote:
| yes, this! thank you good post
| altairprime wrote:
| Note that one could email the mods to de-clickbait/enrage the
| title, especially with such a concrete point as this comment's.
| (I haven't done so as TIL is a poor basis for such an
| argument.)
| dang wrote:
| Ok, we've deposed Edison from the title above.
| sghiassy wrote:
| I've always wondered about these new High-Voltage DC (HVDC)
| transmission lines.
|
| I always thought AC's primary benefit was its transmission
| efficiency??
|
| Would love to learn if anyone knows more about this
| cjbgkagh wrote:
| https://en.wikipedia.org/wiki/High-voltage_direct_current
| adgjlsfhk1 wrote:
| AC is less efficient than DC at a given voltage. The advantage
| of AC is that voltage switching is cheap, easy and efficient.
| Switching DC voltage is way harder, more expensive, and less
| efficient. However the switching costs are O(1) and the
| transmission losses are O(n) so for some distance (currently
| somewhere around 500 km) it's worth paying the switching cost
| to get super high voltage DC. The big thing that's changed in
| the last ~30 years is a ton of research into high voltage
| transistors, and fast enough computers to do computer
| controlled mhz switching of giant high power transistors. These
| new super fancy switching technologies brought the switching
| costs down from ludicrous to annoyingly high.
| arijun wrote:
| > AC is less efficient than DC at a given voltage
|
| To expand on this, a given power line can only take a set
| maximum current and voltage before it becomes a problem. DC
| can stay at this maximum voltage constantly, while AC spends
| time going to zero voltage and back, so it's delivering less
| power on the same line.
| adgjlsfhk1 wrote:
| this iirc is the smallest of 3 problems. the other 2 are
| skin effect (AC wires only store power on the outside of
| the wire) and capacitive effects (a write running parallel
| to the ground is a capacitor and AC current is equivalent
| to constantly charging and discharging the capacitor)
| manwe150 wrote:
| That's true, but my understanding is the main contributor
| is skin effect, since AC travels only on the surface of the
| wire, while DC uses the whole area, resulting in lower
| resistance loss (https://en.wikipedia.org/wiki/Skin_effect)
| adiabatichottub wrote:
| Maybe if by "same voltage" we mean DC voltage the same as
| AC peak voltage. When we talk about AC voltage we are
| referring to root-mean-square (RMS) voltage. It's kind of
| like saying the average, though for math reasons the
| average of an unbiased sine wave is 0. Anyhooo, 1 VRMS into
| a load will produce the same power as 1VDC. If AC delivered
| less power than DC at the same voltage then life would be
| very confusing.
| cogman10 wrote:
| The primary benefit of AC is it's really easy to change the
| voltage of AC up or down.
|
| The transmission efficiency of AC comes from the fact that you
| can pretty trivially make a 1 megavolt AC line. The higher the
| voltage, the lower the current has to be to provide the same
| amount of power. And lower current means less power in line
| loss due to how electricity be.
|
| But that really is the only advantage of AC. DC at the same
| voltage as AC will ultimately be more efficient, especially if
| it's humid or the line is underwater. Due to how electricy be,
| a change in the current of a line will induce a current into
| conductive materials. A portion of AC power is being drained
| simply by the fact that the current on the line is constantly
| alternating. DC doesn't alternate, so it doesn't ever lose
| power from that alternation.
|
| Another key benefit of DC is can work to bridge grids. The
| thing causing a problem with grids being interconnected is
| entirely due to the nature of AC power. AC has a frequency and
| a phase. If two grids don't share a frequency (happens in the
| EU) or a phase (happens everywhere, particularly the grids in
| the US) they cannot be connected. Otherwise the power
| generators end up fighting each other rather than providing
| power to a load.
|
| In short, AC won because it it was cheap and easy to make high
| voltage AC. DC is comming back because it's only somewhat
| recently been affordable to make similar transformations on DC
| from High to low and low to high voltages. DC carries further
| benefits that AC does not.
| prezk wrote:
| Important factor is that AC at given nominal voltage V swings
| between 1.41V and -1.41V, so it requires let's say 40%
| better/thicker insulation than the equivalent V volts DC line.
| This is OK for overhead lines (just space the wires more) but
| is a pain for buried or undersea transmission lines; for that
| reason, they tend to use DC nowadays.
|
| BTW, megavolt DC DC converters are a sign to behold:
| https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...
| topspin wrote:
| > I always thought AC's primary benefit was its transmission
| efficiency??
|
| There are many factors involved, and "efficiency" is only one.
| Cost is the real driver, as with everything.
|
| AC is effective when you need to step down frequently. Think
| transformers on poles everywhere. Stepping down AC using
| transformers means you can use smaller, cheaper conductors to
| get from high voltage transmission, lower voltage distribution
| and, finally lower voltage consumers. Without this, you need
| massive conductors and/or high voltages and all the costs that
| go with them.
|
| AC is less effective, for instance, when transmitting high
| power over long, uninterrupted distances or feeding high
| density DC loads. Here, the reactive[1] power penalty of AC
| begins to dominate. This is a far less common problem, and so
| "Tesla won" is the widely held mental shortcut. Physics doesn't
| care, however; the DC case remains and is applied when
| necessary to reduce cost.
|
| [1] https://en.wikipedia.org/wiki/Electrical_reactance
| umvi wrote:
| I don't understand why new houses don't just have one high
| quality AC/DC converter so you can just use LED lighting without
| every bulb needing its own AC/DC converter. I imagine the light
| bulb cartel wouldn't really like that.
| bluGill wrote:
| It wouldn't work. leds need low voltages, meaning massive
| wires. you can run the voltage change on ac or dc. Ac just
| needs a few capacters to smooth the wave out.
| throw0101d wrote:
| > _I don 't understand why new houses don't just have one high
| quality AC/DC converter so you can just use LED lighting
| without every bulb needing its own AC/DC converter._
|
| IEEE 802.3bt can deliver up to 71W at the destination: just
| pull Cat 5/6 everywhere.
|
| *
| https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...
|
| * https://www.usailighting.com/poe-lighting
| elcritch wrote:
| And pay $60 per Ethernet POE+ light bulb.
| throw0101d wrote:
| > _And pay $60 per Ethernet POE+ light bulb._
|
| In the commercial/industrial space this may be worth it:
| how long do these bulbs last? how much (per hour
| (equivalent)) do you pay your facilities folks? how much
| time does it take for employees or tenants to report an
| outage and for your folks to get a ladder (or scissor lift)
| to change the bulb?
| fortran77 wrote:
| Do you want your house to burn down? Lower voltages for LED
| lights mean higher current.
| bigiain wrote:
| That's traded off against the increase efficiency of LED
| lighting, at least compared to incandescent lighting. An LED
| "equivalent replacement" for a typical incandescent globe is
| down around 1/10th of the power. A 7Watt LED bulb is
| typically marketed as "60W equivalent". If that configured as
| a bunch of LEDs in series (or series/parallel) that need
| 12VDC, it's right about the same current draw as the 120V 60W
| incandescent equivalent. (Or perhaps double the current for
| those of us who get 220VAC out of our walls.)
|
| (Am I just showing my age here? How many of you have ever
| bought incandescent globes for house lighting? I vaguely
| recall it may be illegal to sell them here in .au these days.
| I really like quartz halogen globes, and use them in 4 or 5
| desk lamps I have, but these days I need to get globes for em
| out of China instead of being able to pick them up from the
| supermarket like I could 10 or 20 years ago.)
| Majromax wrote:
| With modern technologies, that's power over ethernet or USB-C.
| Other comments in this thread point out that the telephone
| service also routinely used 48V for the ring signal.
|
| However, higher DC voltage is riskier, and it's not at all
| standard for electrical and building code reasons. In
| particular, breaking DC circuits is more difficult because
| there's no zero-crossing point to naturally extinguish an arc,
| and 170V (US/120VAC) or 340V (Europe/240VAC) is enough to start
| a substantial arc under the right circumstances.
|
| Unfortunately for your lighting, it's also both simple and
| efficient to stack enough LEDs together such that their forward
| voltage drop is approximately the rectified peak (i.e.
| targeting that 170/340V peak). That means that the bulb needs
| only one serial string of LEDs without parallel balancing,
| making the rest of the circuitry (including voltage regulation,
| which would still be necessary in DC world) simpler.
| fragmede wrote:
| because shorts and voltage loss are a real issue at that scale.
| gizmo686 wrote:
| LED light bulbs exist exclusively for compatibility with Edison
| sockets. Every LED fixture I have seen had a single transformer
| for the entire fixture; and that transformer was reasonably
| separate from the LEDs themselves.
| ianburrell wrote:
| What voltage do you use? Most DC stuff wants low voltage
| (5-48V), but appliances need higher voltage like AC-level to
| get enough power over existing wiring. The result is DC-DC
| converters every place that have transformers now.
|
| The gain from DC-DC converters is small and DC devices are
| small part of usage compared appliances. There is no way will
| pay back costs of replacing all the appliances.
| amluto wrote:
| Every decent LED would then need ... a switching power supply.
| LEDs are _current_ -driven devices, and you get the best
| efficiency if you use an actual current-controlled supply. And
| those ICs are very, very cheap now.
|
| The part that would genuinely be cheaper is avoiding
| problematic flicker. It takes a reasonably high quality LED
| driver to avoid 120Hz flicker, but a DC-supplied driver could
| be simpler and cheaper.
| adrr wrote:
| Our houses should be DC. So wasteful to have all these bricks to
| change to AC to DC.
| bandrami wrote:
| I've worked overseas a lot and one thing that's really
| different from 2 decades ago is that I simply don't need a
| step-down transformer anymore because every single thing I plug
| in converts to DC (or otherwise accepts dual-voltage) anyways.
| So I have a giant collection of physical plug adapters because
| every device I use just needs to fit into the socket and takes
| care of it from there.
|
| (My stand mixer is the lone sad exception)
| 747fulloftapes wrote:
| Agreed!
|
| I spent a few years getting flown out around the world to
| service gear at different datacenters. I learned to pack an
| IEC 60320 C14 to NEMA 5-15R adapter cable and a dumb, un-
| protected* NEMA 5-15R power strip. While on-site at the
| datacenters, an empty PDU receptacle was often easy to find.
| At hotels, I'd bring home a native cable borrowed from or
| given to me by the native datacenter staff or I'd ask the
| hotel front desk to borrow a "computer power cable," (more
| often, I'd just show them a photo) and they generally were
| able to lend me one. It worked great. I never found a power
| supply that wasn't content with 208 or 240V.
|
| Example adapters: https://www.amazon.com/dp/B0FD7PHB7Y or
| https://www.amazon.com/dp/B01IBIC1XG
|
| *: Some fancier power strips with surge suppression have a
| MOV over-voltage varistor that may burn up if given 200V+,
| rendering the power strip useless. Hence, unprotected strips
| are necessary.
| ericd wrote:
| Something to consider, and something I got a vivid
| demonstration of while playing with solar panels, DC arcs
| aren't self-extinguishing, unlike AC arcs. At one point I stuck
| a voltage probe in, and the arc stuck with it as I pulled the
| probe away. It also vaporized the metal tip of the probe.
|
| My understanding is that DC breakers are somewhat prone to
| fires for this reason, too.
| bigiain wrote:
| Heh - I vaporised a fairly large soldering iron tip (probably
| 4mm copper cylindrical bar?), when I fucked up soldering a
| connector to a big 7 cell ~6000mAHr LiPo battery and shorted
| the terminals. Quite how I didn't end up blind or in hospital
| I don't know. It reinforced just how much respect you need to
| pay to even low-ish voltage DC when the available current was
| likely able to exceed 700A by a fair margin momentarily. I
| think those cells were rated at 60C continuous and 120C for 5
| seconds.
| ericd wrote:
| heh man, I'm glad you got out of that easy, I definitely
| wore safety glasses 100% of the time after my experience. I
| think a lifetime of experience with dangerous wall outlets
| and harmless little 1.5V/9V DC cells teaches us the wrong
| lessons about DC safety. I've since heard stories of
| wrenches _exploding_ when they fall across EV high voltage
| battery terminals. Wrenches aren 't supposed to be
| explosive.
|
| The electricians I was working with also told me stories
| about how with the really big breakers, you don't stand in
| front of it when you throw it, because sometimes it can
| turn into a cloud of molten metal vapor. And that's just
| using them as intended.
| bluGill wrote:
| Amps - the old 48vdc telco data centers vaporized wrenchs
| once in a while.
| jacquesm wrote:
| Those harmless 9V DC cells can do a lot of damage if you
| use them right.
| sobjornstad wrote:
| This reminds me of the sailor who [decided](https://darwi
| nawards.com/darwin/darwin1999-50.html) to measure his
| internal resistance by pushing probes through the skin on
| his thumbs and electrocuted himself with the 9V
| multimeter battery.
| jacquesm wrote:
| Mythbusters time. Salty fluids can be remarkably
| conductive. Blood qualifies. What's interesting though is
| that you have to wonder if there isn't some contributing
| factor here, as a kid I did this quite a few times, so
| that's one more for that list of stuff that could have
| killed me. At the same time: I didn't have nice
| insulation piercing tips back then (I _do_ now) and that
| may be what saved me. I will definitely not try this
| again.
|
| Another story in the same line is that I heard that a
| horse got killed by contact with a lantern battery, but I
| don't have any reference for that, just a story by a
| family member that collected coaches.
| scheme271 wrote:
| A bunch of those big breakers require two people. One
| person in a flash suit and another with a 2m long pole
| around the first person. That way if an arc flash
| happens, the second person can yank the first person to
| safety without also getting hurt.
| pocksuppet wrote:
| Why don't they use the pole to flip the breaker from 2m
| away?
| defrost wrote:
| Ruins the fun and interrupts instilling respect deep into
| the bones of interns.
|
| _Allegedly_
|
| While on "work experience" from high school I was put on
| washing power lines coming straight out of the local
| power station near the ocean - lots of salt buildups to
| clear.
|
| Same deal, flashover suits and occasional arcs .. and
| much laughter from the ground operators who drifted the
| work bucket close.
| jacquesm wrote:
| You got super lucky.
| bigiain wrote:
| Yep. Super super lucky. I suspect my reading glasses are
| the only reason I can still see anything.
| jacquesm wrote:
| I have a couple of those narrow escapes one of which led
| me to put a significant chunk of Eastern Amsterdam out of
| power. Another involved Beryllium oxide. 9 lives are
| barely enough.
| bigiain wrote:
| I would read that book...
| jacquesm wrote:
| 'Stupid stuff I've done and survived'...
| swamp_donkey wrote:
| Ah! Perhaps you are a member of the gigawatt club?
| Eligible for entry once you have accidentally tripped off
| 1000 MW of load or generation! No sweeping that under the
| table
| jacquesm wrote:
| I'm the idiot that sent a fairly high voltage spike into
| the grid setting off a cascade. Even years later I do not
| fully understand how it could happen, you'd think the
| grid would be low impedance enough to absorb a spike like
| that. But it set off a cascade on a part of the local
| grid that was known to be weak.
| bigiain wrote:
| Somehow I simultaneously desperately want to be in that
| club, and never want to be responsible for an event that
| would let me join that club...
| toast0 wrote:
| > DC arcs aren't self-extinguishing, unlike AC arcs. At one
| point I stuck a voltage probe in, and the arc stuck with it
| as I pulled the probe away. It also vaporized the metal tip
| of the probe.
|
| It would have self-extinguished if you waited long enough for
| the probe to vaporize.
| KaiserPro wrote:
| > My understanding is that DC breakers are somewhat prone to
| fires for this reason, too.
|
| I think its that DC breakers are more expensive, so people
| use AC rated breakers instead. They are both rated for 400v
| @10 amps, its the same thing right?
|
| It turns out they are not, and most people, even electronics
| types rarely play with 200v+ of DC.
| ericd wrote:
| Yeah, I think this array was pushing 350-400V
| kccqzy wrote:
| That's actually a recent phenomenon. Before the age of
| electronics most household appliances either worked with AC or
| DC equally well (like incandescent bulbs) or worked well with
| AC only given the technology at the time (think anything with a
| motor, fans, HVAC compressors etc).
| analog31 wrote:
| Taking it to an extreme, the house I lived in while in grad
| school had wall lamp fixtures that doubled as electric and
| gas lamps. At some point I imagine it would have been
| possible to choose between using electric or gas by either
| flipping the switch or turning a valve. They said "Edison
| Patent" on them. We could have lit the house on AC, DC, or
| gas.
|
| Thinking about the failure modes gave me the heebie jeebies,
| but the gas had been disconnected ages prior.
| jazzyjackson wrote:
| It's kind of fun that light switches predate electricity. I
| think you used to turn a key, I guess you were turning a
| valve? Now that I think of it using a key to operate a
| valve makes a lot of sense but you don't see it too often,
| well, I guess you want to turn things off without needing
| to find a key...
| eszed wrote:
| I lived in a 19th century house in San Francisco that had
| gorgeous plaster work medallions on the ceilings - think
| cherubs and fruits - in the middle of which were the light
| fixtures. One day my dumb-ass flatmate made an ill-advised
| attempt to DIY his light fixture and cracked the still-
| active gas line embedded in the ceiling. Sometime in the
| 1920s - the date was printed on a sticker in the electrical
| panel - when they electrified the house, they'd wrapped the
| electrical wires around the gas pipes, and left them
| otherwise in situ. Crazy stuff.
| torginus wrote:
| I've had discussed with people familiar with the matter, and
| they convinced me its really not worth it for many reasons, the
| main one being safety - DC arcs are self sustaining - AC
| voltage constantly goes to zero, so if an arc were to form, it
| gets auto extinguished when the voltage drops. With DC this
| never happens, meaing every switch or plug socket can create
| this nice long arcs and is a potential fire hazard.
| adiabatichottub wrote:
| Really depends on what we're talking about. A lot of
| electrical safety equipment has a DC rating, usually
| something like 90VDC/300VAC. Also, most DC equipment just
| isn't going to have the stored energy to generate a big arc.
| Well, except batteries, and we're already piling them all
| around us.
| torginus wrote:
| I mean it depends, but for dual rated stuff has both a
| voltage and current limit, both of which are way lower.
| Like typically a 230V/20A AC switch can switch 24VDC/2A.
| And the energy is not in the equipment, its in the mains
| (or batteries like you said, or PV panels)
| adiabatichottub wrote:
| Right, but that's why I mentioned safety equipment. Your
| common DIN-mount UL-489 branch circuit breaker will be
| rated for the same trip current, same short circuit
| current rating (SCCR), but lower voltage. So you can use
| the same wiring and breakers as you might have with AC
| and your 48V battery bank won't vaporize the $5 hardware
| store toggle switch that somehow became a shunt.
| torginus wrote:
| I mean, most AC circuit breakers use electromagnets to
| trip on overcurrent (as well as bimetallic strips using
| thermal methods for sustained high current).
|
| Electromagnets dont work for DC, so your breaker will
| never trip. For thermal protection, you need current, so
| that checks out, and it would make sense for it to be
| rated under 50V as thats considered the highest voltage
| thats not life threatening on touch.
|
| PV Batteries in general have a very high current (100s of
| A) at ~50Vish volts, so I dont think there's a major
| usecase for using household breakers for them.
|
| Im still not getting your point BTW, switches and
| breakers are two separate things, with different
| workings, and household (and datacenter) DC would be I
| think around 400ish V, which is a bit higher than the
| peak voltage of AC, but still within the arc limits of
| household wiring (at least in 230V countries).
|
| The advantage of DC is that you use your wiring more
| efficiently as the mean and peak wattage is the same at
| all times. Going with 48V would mean high resistive
| losses.
| adiabatichottub wrote:
| > Electromagnets dont work for DC, so your breaker will
| never trip.
|
| If electromagnets don't work for DC then what am I
| supposed to do with this pile of DC solenoids and relays?
| ;)
|
| > PV Batteries in general have a very high current (100s
| of A) at ~50Vish volts, so I dont think there's a major
| usecase for using household breakers for them.
|
| That's what the SCCR rating is for. When there's a fault
| you're going to have a LOT of current flowing until your
| safety kicks in. Something like the grid or a battery
| bank will happily provide thousands of amps almost
| instantaneously. Breakers designed for protecting
| building wiring are rated for this. Now, most household
| breakers aren't dual DC/AC rated, but you can actually
| buy DC rated breakers that fit in a home panel (Square D
| QO series).
|
| > Im still not getting your point BTW, switches and
| breakers are two separate things, with different
| workings, and household (and datacenter) DC would be I
| think around 400ish V, which is a bit higher than the
| peak voltage of AC, but still within the arc limits of
| household wiring (at least in 230V countries).
|
| My point is that there isn't any material reason why DC
| can't be as safe as AC, all the proper safety equipment
| already exists. Extinguishing a DC arc during a fault is
| a solved problem for equipment at household scale.
|
| > The advantage of DC is that you use your wiring more
| efficiently as the mean and peak wattage is the same at
| all times. Going with 48V would mean high resistive
| losses.
|
| I just mentioned 48V because it's a common equipment
| voltage for household DC systems. 400V would be good for
| big motors and resistive heating loads.
|
| Regarding DC vs AC and wiring efficiency, talking about
| mean vs peak wattage just confuses the issue. 1 volt DC
| is 1 volt RMS. It is an apples-to-apples comparison. If
| you want to say "we can use 170VDC or 120VAC with the
| same insulation withstand rating, and at lower current
| for the same power", then that is absolutely true. But
| your common 600V THHN building wire won't care if you're
| using 400V AC or DC, so it's mostly immaterial.
| jacquesm wrote:
| The 'what is safer' question for DC and AC at the same
| effective current and power has a mixed set of answers
| depending on conditions. For instance, DC is more likely to
| cause your muscles to contact and not let go (bad), but AC is
| more likely to send your heart into ventricular fibrillation
| (sp?, also bad).
|
| AC arcs are easier to extinguish than DC arcs, but DC will
| creep much easier than AC and so on.
|
| From a personal point of view: I've worked enough with both
| up to about 1KV at appreciable power levels and much higher
| than that at reduced power. Up to 50V or so I'd rather work
| with DC than AC but they're not much different. Up to 400V or
| so above that I'd much rather have AC and above 400V the
| answer is 'neither' because you're in some kind of gray zone
| where creep is still low so you won't know something is amiss
| until it is too late. And above 1KV in normal settings (say,
| picture tubes in old small b&w tvs and higher up when they're
| color and larger) and it will throw you right across the room
| but you'll likely live because the currents are low.
|
| HF HV... now that's a different matter and I'm very
| respectful of anything in that domain, and still have a burn
| from a Tronser trimmer more than 45 years after it happened.
| Note to self: keep eye on SWR meter/Spectrum analyzer _and_
| finger position while trimming large end stages.
| Tempest1981 wrote:
| > DC will creep much easier than AC
|
| Can you say more about "creep"? Is the resistance changing?
| Or is material actually migrating?
|
| Also curious why it's worse using DC.
| jacquesm wrote:
| https://www.eevblog.com/forum/beginners/understanding-
| high-v...
| Tempest1981 wrote:
| Thanks Jacques. So creepage is when current flows/arcs
| across the surface of an insulator, vs through the air.
| And it's worse with DC due to its unidirectional nature.
| Worsens when pollution builds up, or the surface
| degrades.
| jacquesm wrote:
| Indeed. And it's a really nasty thing to properly protect
| against because that pollution, especially with stuff
| that is unattended for a long time has a habit of ending
| up much worse than your worst fantasies. I've taken more
| than one electrocuted mouse out of the HV section of
| older color TVs for instance. Up to 250V or so it is
| manageable, above that you can get the weirdest problems
| including completely invisible arcing where the only
| giveaway is the ozone smell and the occasional click.
| Looking at HV circuitry in the dark or by putting a flame
| near a suspect spot is a great way to spot these kind of
| issues.
| bigiain wrote:
| Sure, maybe?
|
| If your house gets 800V DC you're still gonna need "bricks" to
| convert that to 5VDC of 12VDC (or maybe 19VDC) that most of the
| things that currently have "bricks" need.
|
| And if your house gets lower voltage DC, you're gonna have the
| problem of worth-stealing sized wiring to run your stove, water
| heater, or car charger.
|
| I reckon it'd be nice to have USB C PD ports everywhere I have
| a 220VAC power point, but 5 years ago that'd have been a USB
| type A port - and even now those'd be getting close to useless.
| We use a Type I (AS/NZS 2112) power point plug here - and that
| hasn't needed to change in probably a century. I doubt there's
| ever been a low voltage DC plug/socket standard that's lasted
| in use for anything like that long - probably the old "car
| cigarette lighter" 12DC thing? I'm glad I don't have a house
| full of those.
| jwilliams wrote:
| There are niches where DC makes sense - low-voltage lighting,
| USB/LED ecosystems.
|
| Once you get into higher power (laptops and up), switching and
| distribution get harder, so the advantages fade.
|
| For bigger appliances (fridge, etc), AC is fine + practical.
| adiabatichottub wrote:
| Your modern fridge is probably going to have an inverter-
| driven motor, so you're right back to using DC.
| adrr wrote:
| All modern appliances and HVACs are using inverter drive
| motors for efficiency. Brushless DC motors are more
| efficient though.
| userbinator wrote:
| "Brushless DC motors" are actually just AC synchronous
| motors.
| epx wrote:
| Having a single big DC converter at a home would help a lot
| with power factor (LED lamps connected directly to AC have
| terrible power factor).
| Mistletoe wrote:
| Modern bricks really aren't that inefficient though. An Apple
| charger is like 90% efficient. A DC to DC converter is about
| that efficient or worse.
| catlikesshrimp wrote:
| The power adapters became so efficient that we have to
| transition to wireless charging to keep it down
|
| The irony...
| flowerthoughts wrote:
| I'm renovating a house, and have been considering 24V or 48V DC
| outlets in a few rooms. Semiconductors become more expensive
| above ~32V, so 24V might be the sweetspot.
|
| However, there's also PoE (24 or 48V!), so maybe that's the
| right approach. It's not like each outlet is going to run a
| heater anyway.
| fc417fc802 wrote:
| Lower voltage makes voltage drop across the line
| proportionally worse. Depending on the purpose PoE is
| probably the way to go since the wiring and hardware is all
| standardized and safety certified.
|
| Unless you mean running AC and installing inverters in the
| wall? What is this even for? All my electronics are DC but
| critically they all require different voltages. The only
| thing I might benefit from would be higher voltage service
| because there are times that 15 A at 120 V doesn't cut it.
| Aloisius wrote:
| This article seems to imply that 800V DC is high-voltage DC, but
| that seems quite low.
| MathMonkeyMan wrote:
| Quite low compared to a power utility's HVDC, but quite high
| compared to the 5/12/24 V output of most AC/DC converters used
| for electronics.
| bigiain wrote:
| I think there'a a regulatory "Low Voltage" definition of "below
| 50V", which has implications around whether you need to be a
| licensed electrician to install it or not. Anything above that
| is - for at least some purposes - considered "High Voltage".
|
| Other people, of course, have other definitions of high
| voltage:
|
| "This resonant tower is known as a Tesla coil. This particular
| one is just over 17 feet tall and it can generate about a
| million volts at 60,000 cycles per second."
|
| and:
|
| "This pulse forming network can deliver a shaped pulse of over
| 50,000 amps with a total energy of about 1,057 times the tower
| primary energy"
|
| https://www.youtube.com/watch?v=RoGbrgOhPes
| KnuthIsGod wrote:
| Waiting for home DC.
|
| It is silly to have AC to DC converters in all of my wall
| connected electronics ( LED bulbs, home controller, computer
| equipment etc )
| jacquesm wrote:
| Not going to happen. For the same reason that the US never
| converted to a higher domestic voltage even though there are
| many practical advantages. The transition from one system to
| another at the consumer level would be terrible, even if there
| would be some advantage (and I'm not sure the one you list is
| even valid, you'd get DC-DC converters instead because your
| consumers typically use a lower voltage than the house
| distribution network powering your sockets) it would be offset
| by the cost of maintaining two systems side by side for
| decades.
|
| You could wire your house for 12, 24 or 48V DC tomorrow and
| some off-grid dwellers have done just that. But since inverters
| have become cheap enough such installations are becoming more
| and more rare. The only place where you still see that is in
| cars, trucks and vessels.
|
| And if you thought cooking water in a camper on an inverter is
| tricky wait until you start running things like washing
| machines and other large appliances off low voltage DC. You'll
| be using massive cables the cost of which will outweigh any
| savings.
| manwe150 wrote:
| I suppose that still begs the question somewhat, since the US
| does have 240V (2 phase) already driving many appliances. Why
| hasn't it ever become standard for luxury kitchens to have a
| European-style outlet for use with a European kettle? I know
| the US already has a different 240V plug shape, so it might
| have to be an unlicensed installation, but surely someone
| wanted hot tea faster and did that calculus before?
| jacquesm wrote:
| Well, as you say, it would not be according to code and the
| insurance company might have something to say about it.
| It's also single phase but not quite the way you do it in
| the USA, it would be a neutral and a phase whereas in the
| USA I think it is 2x110. Finally, it's 50 Hz rather than 60
| which would work fine for resistive loads but not so well
| for inductive ones such as transformers and motors.
|
| In all likely not worth the trouble. When I moved to Canada
| I gave away most of my power tools for that reason and when
| I moved back I had to do that all over again.
| aidenn0 wrote:
| > In all likely not worth the trouble. When I moved to
| Canada I gave away most of my power tools for that reason
| and when I moved back I had to do that all over again.
|
| If you ever have to do it again, you can probably get a
| transformer rated high enough for power-tools for cheaper
| than replacing all of your power tools.
| jacquesm wrote:
| Of course you can. That's kind of obvious. It is also
| highly impractical. Besides the frequency delta you end
| up having to lug a heavy transformer along and then you
| have to alternate it across your tools so you don't end
| up frying the transformer.
| mauvehaus wrote:
| The line frequency tends to screw with things with motors
| too. Moved from the US to Belgium back when compact
| cassette was a common format for music.
|
| Killed a few tapes with a transformer on a US tape deck
| before buying a 220V 50Hz unit. No, I don't remember if
| the pitch was grossly off, but I'm guessing it wasn't.
| ianburrell wrote:
| You can run 240V circuit to kitchen for kettle and put in
| NEMA 6 outlet. But few people care about fast boil and
| importing European kettle. Most people use the microwave or
| stovetop, and 120V kettles are fine in most cases. It will
| never become a standard thing.
| tbrownaw wrote:
| > _I know the US already has a different 240V plug shape,
| so it might have to be an unlicensed installation, but
| surely someone wanted hot tea faster and did that calculus
| before?_
|
| How expensive would a proper AC->DC->AC brick for that
| power level be?
| jacquesm wrote:
| Not so simple, you'd have to use a 'drier' or 'welder'
| socket for that otherwise you won't have enough power. A
| single circuit in Europe is 240V 16A or 3840W!
|
| A pure sinewave inverter for that kind of power is maybe
| 600 to 1000 bucks or so, then you'd still need the other
| side and maybe a smallish battery in the middle t
| stabilize the whole thing. Or you could use one of those
| single phase inverters they use for motors.
| jcalvinowens wrote:
| I wired a UK kettle to an unused 240V range outlet in the
| US once. It was amazing, boiled a liter of water in just
| under a minute. Obviously kinda sketchy.
| jacquesm wrote:
| That's more like it :)
| zahlman wrote:
| "Wired"?
|
| ...There was some kind of switch involved, I hope?
| vessenes wrote:
| Most important comment here!! I would love to buy like a
| 6kw battery induction kettle for the states. As far as I
| can tell, they don't exist.
| fc417fc802 wrote:
| Ahckhually US residential is split single phase, not two
| phase. https://en.wikipedia.org/wiki/Split-
| phase_electric_power
|
| I think the answer to your question is that it mostly
| doesn't matter for personal mug size quantities of hot
| water and if it does matter to you there are readily
| available competing options such as dedicated taps for your
| kitchen sink.
|
| Perhaps the biggest reason is that a traditional kettle on
| any half decent electric range will match if not exceed the
| power output of any imported electric kettle. Many even go
| well beyond that with one burner marked "quick boil" or
| similar.
| lostlogin wrote:
| I use an induction stove on maximum to boil water as I
| get irritated at the time it takes to boil water with
| 240v.
|
| I'm surprised that American exceptionalism can tolerate
| half powered sockets.
| bregma wrote:
| > but surely someone wanted hot tea faster
|
| No one in the USA drinks hat tea. The choices (and it tends
| to be regionally-based) is sweet or unsweet tea. No need to
| boil a kettle quickly for that.
| margalabargala wrote:
| What? Plenty of people in the US drink hot tea.
| mauvehaus wrote:
| > No one in the USA drinks h[o]t tea.
|
| There are dozens of us.
|
| Perplexingly I was traveling in one of the iced tea
| regions of the country in need of a cup of hot tea, and
| they had no way to make it. Like, you have a commercial
| coffee maker and hot cups, the coffee maker has a
| hot(ish) water tap. All you need is a $4 box of teabags
| that'll last until the heat death of the universe. Nope.
| vel0city wrote:
| As a counter argument, things like pour over coffee is
| getting to be more popular in the US and older drip
| coffee makers seem to be getting slightly less popular.
|
| Still though, I don't seem to see most of those people
| seriously clamoring for the electric kettle to go a bit
| faster. The cost for the wiring difference and dealing
| with odd imported kettles just isn't worth it generally.
| zahlman wrote:
| > The choices (and it tends to be regionally-based) is
| sweet or unsweet tea.
|
| ... Unless you're buying it pre-made, does this not still
| start with making hot tea the regular way? Or what
| exactly are you doing with the tea bags and loose tea
| from the supermarket?
| xoxxala wrote:
| Technology Connections did this with an EV battery charger:
|
| https://youtu.be/INZybkX8tLI
| SoftTalker wrote:
| I'm not sure it's likely, but I could see DC lighting start
| to happen in new construction. Have a single AC-to-DC
| converter off the main service entrance that powers hard-
| wired LED lighting fixtures in the house. Would probably be
| better than running the individual (and usually very low
| quality) converters in dozens of standard LED light bulbs.
| Would need to be standardized, codified, etc. so probably not
| happening soon.
| ansgri wrote:
| Would be more practical to have a single 50-300W AC-DC 24V
| PSU per room or group of rooms, then pull relatively short
| DC cables to each light. A multichannel light controller
| could also be placed nearby, and then if you need fully-
| featured brightness and color control, only a small PWM
| amplifier could be placed at each light if distance from
| controller to each light is too long to transmit PWM power
| directly.
| wincy wrote:
| I just wish I could run my air conditioner and my desktop
| computer at the same time without flipping the breaker. The
| RTX 5090 is a space heater and will easily peg at the 600W
| it's rated for, and so with that and an air conditioner
| window unit, I have to run a long cable from another unused
| room if I want to do anything that stresses the video card.
| jacquesm wrote:
| You can use nvidia-smi to reduce the powerdraw of the card
| to just below what will trip the breaker.
| zahlman wrote:
| If you're running an air conditioner and a "space heater"
| at the same time it might be worth reconsidering your
| priorities.
|
| I can watch 1080p video on YouTube and it runs in an up-to-
| date web browser using less than 50% CPU on 12-year-old
| hardware with 8GB of RAM and a graphics card that was a
| budget option at the time (my searches indicate it draws at
| most 80W, though it expects a 500W PSU for some reason).
| throw0101c wrote:
| > _Not going to happen. For the same reason that the US never
| converted to a higher domestic voltage even though there are
| many practical advantages._
|
| It would be relatively easy for the US to go to 240V: swap
| out single-pole breakers for double-pole, and change your
| NEMA 5 plugs for NEMA 6.
|
| For a transition period you could easily have 240V and 120V
| plugs right next to each other (because of split phase you
| can 'splice in' 120V easily: just run cable like you would
| for a NEMA 14 plug: L1/L2/N/G).
|
| What would be the real challenge would be going from 50 to
| 60Hz.
| rkomorn wrote:
| > What would be the real challenge would be going from 50
| to 60Hz.
|
| Other way around, no? The US is already 60Hz.
|
| Edit: I mostly remember this because the SNES games I used
| to buy in the US and brought back to Europe ran noticeably
| slower.
| zahlman wrote:
| ... or we could have _both_ sets of wiring, and use what 's
| appropriate for the task/appliance?
| ternus wrote:
| The lesser-known instance of this is RV power. When you're
| running off small batteries and solar, you want to make the
| best use of the watt-hours you have, and that means avoiding
| the DC-to-AC-to-DC loop wherever possible. So you run 12V (or
| in newer models, higher voltage) versions of everything,
| upconverting as necessary.
| amluto wrote:
| I am really skeptical that 12VDC power distribution in RVs
| actually saves power compared to a high-quality (hah!) higher
| voltage AC or DC system. 12V is absurdly low and you can't
| easily lose quite a few percent in resistive losses even with
| fairly large cables, and those large cables are quite
| unpleasant to work with and rather dangerous.
| saltyoldman wrote:
| I tried using a microwave off the RV batteries, your
| inverter needs 4/0 cable. Very "fun".
| scarecrowbob wrote:
| Well, having spent some time operating a 12VDC system last year
| when I moved into some shacks, I will say that I find it a lot
| more convenient to run 120VAC.
|
| I end up converting stuff anyhow, because all my loads run at
| different voltages- even though I had my lights, vent fan, and
| heater fans running on 12V I still ended up having to change
| voltages for most of the loads I wanted to run, or generate a
| AC to to charge my computer and run a rice cooker.
|
| Not to mention that running anything that draws any real power
| quickly needs a much thicker wire at 12V. So you're either
| needing to run higher voltage DC than all your loads for
| distribution and then lowering the voltage when it gets to the
| device, or you simply can't draw much power.
|
| Not that you can't have higher voltage DC; with my newer system
| the line from my solar panels to my charger controller is
| around 350VDC and I can use 10awg for that... but none of the
| loads I own that draw much power (saws, instapot, rice cooker,
| hammond organ, tube guitar amp) take DC :D
| jazzyjackson wrote:
| Catch me wiring my house with 20V USBC ;)
| mauvehaus wrote:
| Do you have a website with your system on it? I have an off-
| grid building I need to add solar to in the next year or so.
| After I fix the foundation and roof, of course. Naturally I'm
| exploring options for item 387 on the todo list instead of
| think about how I'm going to jack the building up.
| scarecrowbob wrote:
| It's a pretty simple system:
|
| 4KW of panels, 400W 48V EG4 6000XP charge controller/
| inverter 3x EG4 LifePower4 48V batteries a raspberry pi
| running solar assistant
|
| I feels like a bit overkill, and there is still a whole
| mppt unused on the 6000xp so I could still double my panel
| input. Also solar assistant tells me that I rarly go below
| 75% battery storage. If I just wanted to run my fridge and
| assorted convenience loads (and ran things like table saws
| off a generator) then I could get away with a lot less of a
| system.
|
| But I'm operating a recording studio, and there were a
| couple days this winter where I had a full-band session and
| a couple days of storms and got down to below 50%.
| est wrote:
| home appliances have lower voltage, like 12V or 5V. The wire
| loss and heat would be a problem.
| hahn-kev wrote:
| It's called USB power delivery
| gwbas1c wrote:
| Assuming you live in a "large" western home, it's impractical.
| Remember, Edison's first power grid operated at 110/220v DC to
| the home. If there was lower voltage (IE, 12 volts) going from
| the street to your walls, the line loss would be _significant._
| It only works in RVs and shacks because the wires are short.
|
| Thus, even if you had DC in the walls, it would be 100+ volts,
| and you'd still have conversion down to the lower voltages that
| electronics use. If you look at the comments in this thread
| from people who work in telco, they talk about how voltage
| enters equipment at -48V and is then further lowered.
| skullone wrote:
| Transitioning? It already happened decades ago. Only smaller
| scale/generic or less proficient "we bought all Dell and HP" use
| AC. At large scale it's been a ton of DC for literally decades.
| And for 70 years in telco and network gear.
| b00ty4breakfast wrote:
| They're still converting from AC to DC at the datacenter, it just
| isn't being stepped down at the perimeter. There is no
| transmission of HVDC going on. This isn't really Edison's
| revenge, more like his consolation price, ha!
| neoCrimeLabs wrote:
| The datacenter I built in 2007 was DC.
|
| Many datacenters I'd been to at that point were already DC.
|
| Didn't think this was that new of a trend in 2026, but also
| acknowledge I did not visit more than a handful of datacenters
| since 2007.
|
| It just seemed like a undenyably logical thing to do.
| jeffbee wrote:
| It's obviously not new. +-400VDC architecture was presented at
| Open Compute last year, which is a fair indicator that the
| presenter had put it into practice at least 5 years prior to
| disclosing it. 48VDC distribution within a rack, and 48-to-1V
| direct regulators for CPUs, were both contributed to OCP 7
| years ago, at which point they were both old hat. And 48VDC
| telco junk is, of course, totally ancient.
| Animats wrote:
| 800V to each rackmount unit, with hot plugging of rack units?
| That's scary. The usual setup at this voltage is that you throw a
| hulking big switch to cut the power, and that mechanically
| unlocks the cabinet. But that's not what these people have in
| mind. They want hot-plugging of individual rackmount units.
|
| GE has a paper about the power conversion design, but it doesn't
| mention the unit to rack electrical and mechanical interface.
| Liteon is working on that, but the animation is rather vague.[2]
| They hint at hot plugging but hand-wave how the disconnects work.
| Delta offers a few more hints.[3] There's a complex hot-plugging
| control unit to avoid inrush currents on plug-in and arcing on
| disconnect. This requires active management of the switching
| silicon carbide MOSFETs.
|
| There ought to be a mechanical disconnect behind this, so that
| when someone pulls out a rackmount unit, a shutter drops behind
| it to protect people from 800V. All these papers are kind of
| hand-wavey about how the electrical safety works.
|
| Plus, all this is liquid-cooled, and that has to hot-plug, too.
|
| [1] https://library.grid.gevernova.com/white-papers-case-
| studies...
|
| [2] https://www.youtube.com/watch?v=CQOreYMhe-M&
|
| [3]
| https://filecenter.deltaww.com/Products/download/2510/202510...
| rdtsc wrote:
| It is a pretty clever design
|
| > When it is detected that the PDB starts to detach from the
| interface, the hot-swap controller quickly turns off the MOSFET
| to block the discharge path from Cin to the system. After the
| main power path is completely disconnected, the interface is
| physically detached, and no current flows at this time
|
| > For insertion, long pins (typically for ground and control
| signals) make contact first to establish a stable reference and
| enable pre-insertion checks, while short pins (for power or
| sensitive signals) connect later once conditions are safe;
| during removal, the sequence is reversed, with short pins
| disconnecting first to minimize interference.
| Animats wrote:
| Yes, I read that. There had better be a backup system.
| MOSFETs tend to fail ON, and there's a megawatt going into
| each rack.
|
| Somehow this seems the wrong approach to AI.
| superxpro12 wrote:
| Fail _spectacularly_
|
| Data center workers are gonna need those big yoink sticks
| and those thick arc-fault bibs that furnace operators wear.
| Animats wrote:
| McMaster-Carr has the personal protective equipment
| required for 800V: Flash protection face shields [1] and
| Class 0 electrical protection gloves.[2]
|
| It's not that bad. It's just ordinary industrial
| protective gear.
|
| [1] https://www.mcmaster.com/products/arc-flash-
| protection-face-...
|
| [2] https://www.mcmaster.com/products/electrical-
| protection-glov...
| dist-epoch wrote:
| Or maybe you can require technicians to be in full-protection
| electrical suits.
| elif wrote:
| As long as you can control for fire, electrical safety seems
| like a temporary condition as robots and intelligent machines
| are cheaper and more available long term solution to hot swap
| blades in datacenter racks.
| QuantumGood wrote:
| I think you're being downvoted for speaking of a complex
| future possibility ("robots and intelligent machines ...
| solution") as if it was a proven commodity. There will be
| many twists and turns in the path to the possible
| reliability, scalability, and cost effectiveness of robots
| and intelligent machines.
| elif wrote:
| Yea I literally said long term but HN voters have such a
| hate boner for anything adjacent to AI
| elif wrote:
| It is a proven commodity already. Just not in our behind-
| the-curve country.
|
| Look at NTT Data or SoftBank.
|
| https://www.softbank.jp/en/sbnews/entry/20250917_01
| elif wrote:
| Dear downvoters: softbank has been optimizing their
| datacenters for robotic technicians since 2020.
|
| They are about to have fully human free datacenters by the
| end of this year.
|
| When you are designing _long term_ goals with datacenters, as
| I explicitly mentioned talking about, you can 't ignore
| automation.
| riedel wrote:
| An EV fast charger can do 1000V, so with a bit of logic that
| sounds doable.
| t0mas88 wrote:
| EV chargers take a different approach. There is no power on
| the connector while you're plugging it in. It then locks in
| place before the contactor closes and power is delivered.
| Unplugging is the same, power is removed before the plug is
| unlocked for release.
| hinkley wrote:
| The power connectors will be on the far side of the rack from
| the service side so shouldn't be a problem for humans touching
| the third rail so to speak.
|
| With that sort of voltage you should be able to use a
| capacitive or inductive sensor to activate a relay.
| mikewarot wrote:
| With a power rail that could supply kiloamps of fault
| current, thus megajoules of energy into an arc, I wouldn't be
| so sure of that.
|
| Copper vapor inhalation is a definite possibility and a
| horrible way to die.
| amluto wrote:
| I wonder how much of the benefit is simpler redundant power
| equipment. For AC, you have standby UPSes and line-interactive
| UPSes and frequency and phase synchronization. And everything
| needs a bit more hold-up time because, in case of failure, your
| new power supply might be at a zero crossing.
|
| For 800V DC, a simple UPS could interface with the main supply
| using just a pair of (large) diodes, and a more complex and more
| efficient one could use some fancy solid state switches, but
| there's no need for anything as complex as a line-interactive AC
| UPS.
| saltyoldman wrote:
| The large brick you have on all your tech when you plug it in is
| the converter. AC works great for some applications, none of them
| really technical in nature.
| fredgrott wrote:
| That is about like aying the band AC DC had its revenge.....
|
| can we stop vibe generating headlines?
| flossly wrote:
| AC is also waaaay safer for households: since the power drop to
| to zero 100x (50Hz) per second switches are cheaper and safer,
| and electrocution is less likely to happen.
| pjdesno wrote:
| 90% of the power in our academic data center goes 13.8kV 3-phase
| -> 400v 3-phase, and then the machines run directly from one leg
| to neutral (230v). One transformer step, no UPS losses, and the
| server power supplies are more efficient at EU voltages.
|
| But what about availability? If you ask most of our users whether
| they'd prefer 4 9s of availability or 10% more money to spend on
| CPUs, they choose the CPUs. We asked them.
|
| There are a lot of availability-insensitive workloads in the
| commercial world, as well, like AI training. What matters in
| those cases is how much computing you get done by the end of the
| month, and for a fixed budget a UPS reduces this number.
| chromacity wrote:
| > and then the machines run directly from one leg to neutral
| (230v)
|
| And then every machine has a switching power supply to convert
| this to low-voltage DC, and then probably random point-of-load
| converters in various places (DC -> AC -> DC again) for stuff
| like the CPU / GPU core, RAM, etc. Each of these stages may be
| ~95% efficient with optimal load, but the losses add up, and
| get a lot worse outside a narrow envelope.
| Dylan16807 wrote:
| Yes, but it's not like any other layouts avoid those issues.
|
| You could feed your servers off fat 12/24/48 volt supplies
| but with how much power a modern server can pull you're
| already converting in bulk even if you don't do that,
| limiting the potential advantages. For running CPU/GPU/RAM,
| there is no other option. When you need hundreds of amps at
| 1-2 volts, you convert that centimeters away if at all
| possible.
|
| A datacenter using DC distribution is still using high
| voltages and stepping them down in layers. The hassle it
| avoids is in other aspects of power delivery.
| poemxo wrote:
| Really you're down for over an hour a year? Unscheduled?
| gwbas1c wrote:
| Anyone notice that 400V and 800V are also used in EV battery
| architecture? I wonder if there's any sharing of technology?
| notorandit wrote:
| It does make a whole lot is sense. The amount of energy you loose
| to convert AC to DC can be humongous . And useless if you produce
| your own power (normally already in DC).
| sholladay wrote:
| Is there anything left in a modern home that really needs or is
| better on AC?
|
| We have some old ceiling and exhaust fans, but I know those can
| be replaced. Our refrigerator is AC, but extended family with an
| off-grid home has a DC refrigerator that cycles way less,
| probably due to multiple design factors but I'm sure the lack of
| transformer heat is part of it. I'm not as sure about laundry
| machine or oven/cooktop options but I believe those are also
| running on DC in the off-grid home without inverters.
|
| Most of these AC appliances also have transformers in them anyway
| for the control boards. It seems kind of insane to me that we are
| still doing things this way.
| Retric wrote:
| Of grid homes are vastly more concerned with the energy
| efficiency of their appliances and thus DC refrigerators
| generally have more insulation. Most AC customers prefer more
| internal volume for food over slightly increased efficiency.
|
| AC motors are using way more power than the puddly control
| boards in most home appliances. So you lose a little efficiency
| on conversion but being 80% efficient doesn't matter much when
| it's 1-5% of the devices energy budget. You generally gain way
| more than that from similarly priced AC motors being more
| efficient.
| sholladay wrote:
| I agree with everything you said, except it seems like a
| false dichotomy. We can clearly build DC refrigerators with
| more or less insulation. We can clearly build them large or
| small. If you want to prioritize volume, then surely you
| could do that with DC. Right?
|
| I know that a long time ago DC-to-DC voltage converters were
| very large in size, which meant AC would win on space
| efficiency. But unless I'm mistaken, that's no longer the
| case. Wouldn't a DC refrigerator with equivalent insulation
| and interior volume have nearly identical exterior dimensions
| as an AC refrigerator?
| Retric wrote:
| > Wouldn't a DC refrigerator with equivalent insulation and
| interior volume have nearly identical exterior dimensions
| as an AC refrigerator?
|
| Sure, but it's important to separate what could be built
| from what is being built based on consumer preferences and
| buying habits. The average refrigerator could be
| significantly quieter, but how often do people actually
| listen to what they are buying? People buying Tesla's
| didn't test drive the actual car they were buying so the
| company deprioritized panel gaps. And so forth, companies
| optimize in ways that maximize their profits not arbitrary
| metrics.
| samus wrote:
| Any appliance with strong motors should be more efficient with
| AC supply. But almost anything else can be regarded as a heater
| that doesn't care much as long as it is fed with the correct
| voltage. Which is actually the core issue.
|
| A DC household would have to choose a trade-off between
| multiple lines with different voltages or fewer voltages that
| need to be adapted to the appliances. And we're right back at
| the AC situation, but worse since DC voltages are more
| difficult to change.
|
| But consumers like datacenters can very well plan ahead and
| standardize on a single DC voltage. They already need beefy
| equipment to deal with interruptions, power sourges, non-sinus
| components, and brownouts, which already involves transformers,
| condensators, and DC conversion for battery storage. Therefore
| almost no additional equipment is required.
| sholladay wrote:
| What qualifies as a strong motor here? Are you comparing to a
| brushed DC motor? Do you think a washer/dryer would have
| worse overall efficiency with a BLDC in a DC home compared to
| what we have today? If so, that's news to me. Where can I
| learn more about that?
|
| The trade-off between, say, one (relatively) high voltage DC
| bus throughout the home vs many branches with lower discrete
| voltages is indeed a problem. With AC, we took the bus
| approach, running 120v everywhere (in the U.S., higher
| elsewhere). I'm inclined to say we should keep doing that for
| flexibility and predictability. But it's a trade off, like
| you said. It would obviously help if regulatory and standards
| bodies came out with official recommendations.
| zarzavat wrote:
| Probably 90% of my devices run 5V DC or similar, but you
| can't run that through a home so you're back to needing AC.
| If you're going to have AC and DC then you might as well
| just have AC.
| sholladay wrote:
| > Probably 90% of my devices run 5V DC or similar,
|
| Indeed. And that's quite normal. Our electrical system
| should serve our modern needs.
|
| > but you can't run that through a home
|
| 5V might be too low for that length of wire. But you
| could most definitely have a low voltage line in your
| house that we could design around, maybe 12V. Electric
| vehicles are moving towards 48V for accessories. It seems
| like lack of a standard is holding us back more than
| anything else.
|
| Or we could just keep doing 120V in the walls, with a DC
| supply. Modern DC-to-DC voltage converters are very
| efficient and small. But maybe I'm wrong. A lot of people
| seem to believe they are still not good enough yet for
| such a change to make sense.
|
| > If you're going to have AC and DC then you might as
| well just have AC.
|
| I arrive at the opposite conclusion. Most things are
| natively DC. So therefore, power in the walls should be
| DC and we should covert it to AC near the endpoint where
| necessary.
| samus wrote:
| Things like washing machines, dryers, dishwashers, air
| conditioners, or fridges spend a lot of energy by running
| powerful electrical motors, which should benefit from AC.
|
| Everything else I can think of in a typical household is
| basically a mere heater that in principle works equally
| well with AC and DC of the correct voltage. Even computers
| can be said to mostly care about the correct voltage since
| AC->DC conversion is vastly easier than voltage conversion.
| tibbydudeza wrote:
| Have a solar system at home and from the panels it is DC into the
| batteries but then the inverter needs to convert it to 220V/50Hz
| AC for home use.
| everdrive wrote:
| "How can we turn this technical story into a story about people
| and their conflicts?"
| BorisMelnik wrote:
| its really wild at all the AC to DC changes. for those non
| electric engineers / hardware hackers (like myself) one of the
| biggest "examples" I've seen of this has been ceiling fans.
|
| Installing a ceiling fan used to be treacherous and so heavy.
| Also loud and buzzy after installed. Now the fans in these things
| are so lightweight and easy.
|
| seeing the same in many more areas (lighting, etc)
| hamdingers wrote:
| Would love to see more mainstream DC lighting options and an
| updated code to match. I just finished a remodel of my workshop
| and blew over a hundred bucks on 14/2 for a 15 amp lighting
| circuit that is unlikely to ever see more than a 1 amps load.
|
| The irony is all the recessed lights I picked out _are_ DC,
| they all have little AC-DC boxes hanging off them using a
| proprietary connector. If I hadn 't needed to pass a rough-in
| inspection going all DC would've been trivial.
| p0w3n3d wrote:
| Hard as a rock! Well it's harder than a rock!
| Xcelerate wrote:
| I set up my own home network with a Vertiv Liebert Li-ion UPS a
| few years ago and was thinking about how inefficient the whole
| process is regarding power. The current goes from AC to DC back
| to AC back to DC. Straight from the UPS as DC would work much
| better, and as I was teaching myself more about networking
| equipment, I was surprised to learn that most of it _isn 't_ DC
| input by default (i.e., each piece of equipment tends to come
| with built-in AC-DC conversion).
|
| Then I started routing ethernet with PoE throughout my house and
| observed that other than a few large appliances, the majority of
| powered devices in a typical home in 2026 could be supplied via
| PoE DC current as well! Lighting, laptops, small/medium
| televisions. The current PoE spec allows up to 100 W, which
| covers like 80% of the powered devices in most homes. I think it
| would make more sense to have fewer AC outlets around the modern
| house and many more terminals for PoE instead (maybe with a more
| robust connector than RJ45). I wonder what sort of energy
| efficiency improvements this would yield. No more power bricks
| all over the place either.
| estimator7292 wrote:
| I think we're slowly, slowly coming around to the idea of
| domestic DC distribution. The vast majority of consumer
| electronics would be perfectly happy to consume 12v. It's
| cheaper, safer, more efficient. Less design work and
| certification on inbuilt AC adapters.
|
| I think it's highly unlikely we'll see mass scale retrofits,
| but if enough momentum builds up, I can see it as a great bonus
| feature for new builds.
|
| I got lucky with my house and every room has a dedicated phone
| line meeting at a distribution panel (a couple of 2x4s with
| screw terminals) built in the 50s. I'm in the process of
| converting it to light duty DC power. The wiring is only good
| for an amp or two, but at 48v that's still significant power
| transmission.
| zahlman wrote:
| > I think it's highly unlikely we'll see mass scale
| retrofits, but if enough momentum builds up, I can see it as
| a great bonus feature for new builds.
|
| I imagine rooftop solar could also source DC for the house
| directly (or via a battery), before hitting the inverter... ?
|
| The main problem I see is educating consumers. Maybe that
| starts with a standard for DC outlets and plugs that can't be
| confused with AC... ?
|
| (Now I'm imagining desktop computers with much simpler power
| supplies; but you'd presumably have to wire for dozens of
| amps incoming...)
| matt-p wrote:
| 48v is what most home battery/solar systems run off. Also
| coincidentally POE, IMO it makes a much more sensible
| candidate as it is still 'safe' while carrying 4x as much
| power for a given cable gauge. Consider laptops are 19 or 20v
| so you would essentially /need/ a minimum of 24v.
| rsync wrote:
| "... throughout my house and observed that other than a few
| large appliances, the majority of powered devices in a typical
| home in 2026 could be supplied via PoE DC current as well!"
|
| We installed 120 LED ceiling lights in our home circa 2020, all
| of which were run with high voltage (romex) and accompanied by
| 120 little transformer boxes that mount inside the ceiling next
| to them.
|
| Later ...
|
| We installed outdoor lighting with low voltage, outdoor rated
| wiring and powered by a 12V transformer[1] and I felt the same
| way you did: why did we use a mile of romex and install all of
| those little mini transformers when we could have powered the
| same lights with 12V and low voltage wire ?
|
| I then learned that the energy draw of running the low-volt
| transformer all the time - especially one large enough to
| supply an entire house of lighting - would more than cancel out
| energy savings from powering lower voltage fixtures.
|
| You don't have this problem with outdoor lighting because the
| entire transformer is on a switch leg and is off most of the
| time.
|
| So ... I like the idea of removing a lot of unnecessary high
| voltage wire but it's not as simple as "just put all of your
| lights behind a transformer".
|
| [1] https://residential.vistapro.com/lex-
| cms/product/262396-es-s...
| eqvinox wrote:
| > I then learned that the energy draw of running the low-volt
| transformer all the time - especially one large enough to
| supply an entire house of lighting - would more than cancel
| out energy savings from powering lower voltage fixtures.
|
| That's not a constraint of physics, you can absolutely build
| a DC power supply that is efficient in a wide load range.
| (Worst case it might involve paralleling and switching
| between multiple PSUs that target different load ranges.) But
| of course something like that is more expensive...
| Dylan16807 wrote:
| > But of course something like that is more expensive...
|
| More expensive than an inefficient unit, but it should
| still be a lot cheaper than 120 separate units, right?
|
| And I expect one big fat unit to do a better job of
| smoothing out voltage and avoiding flicker than a bunch of
| single-light units. Especially because the output
| capacitors are sized for the entire system, but you'll
| rarely have all the lights on at the same time.
|
| Though for efficiency I'd think you'd want 48v and not 12v.
| throw0101d wrote:
| > _I set up my own home network with a Vertiv Liebert Li-ion
| UPS a few years ago and was thinking about how inefficient the
| whole process is regarding power. The current goes from AC to
| DC back to AC back to DC._
|
| With double-conversion, generally yes.
|
| I recently ran across the (patented?) concept of a delta
| conversion/transformer UPS that seems to eliminate/reduce the
| inefficiencies:
|
| * https://dc.mynetworkinsights.com/what-are-the-different-
| type...
|
| * a bit technical: https://www.youtube.com/watch?v=nn_ydJemqCk
|
| * Figures 6 to 8 [pdf]: https://www.totalpowersolutions.ie/wp-
| content/uploads/WP1-Di...
|
| The double-conversion only occurs when there's a 'hiccup' from
| utility power, otherwise if power is clean the double-
| conversion is not done at all so the inefficiencies don't kick
| in.
| zahlman wrote:
| > Lighting, laptops, small/medium televisions. The current PoE
| spec allows up to 100 W, which covers like 80% of the powered
| devices in most homes.
|
| I find it a little hard to imagine that those devices outnumber
| things like stoves, dishwashers, washers/dryers, kettles, hair
| dryers... by 4:1.
|
| Unsure why PoE would be better for LED lighting than the
| standard approach of screwing a bulb directly into AC, either.
| How many lumens do you get out of strip lights these days? And
| you still have AC-DC conversion for whatever's sourcing power
| onto the Ethernet link.
| formerly_proven wrote:
| PoE is also fairly bulky, requires large connectors, and
| either requires a wholly isolated PD or what's basically a
| class 2 DC/DC converter. That's why PoE-powered stuff usually
| has that big transformer cube in it with a lot of clearance,
| slotted PCB, 2-4 kV capacitors etc.
|
| In practice PoE will have lower efficiency than mains
| powered, since it'll usually be at least double conversion,
| often three converters in series, plus the losses of the thin
| network wires, and the relatively high idle losses / poor
| low-load efficiency of the necessarily over-dimensioned PSE.
| sneak wrote:
| I think Ubiquiti (makers of the UniFi wifi products, as well as
| some of the most popular managed PoE switches) also make a ton
| of other PoE products such as the usual stuff like cameras, ip
| phones, network switches, access card readers, door locks, and,
| now, ceiling lights (presumably due to the latest PoE standards
| delivering significant wattage).
|
| It's super nice because you only need to put the UPS/ATS at the
| PoE switch and then you get power redundancy everywhere you
| have ethernet running (i.e. the phones don't go down).
| pdpi wrote:
| > maybe with a more robust connector than RJ45
|
| USB-C could be that connector, using USB-PD instead of PoE.
| Though I'm not sure I'd want to need that much smarts for every
| single power outlet.
| kjs3 wrote:
| Considering the number of times I've sheared off a USB-C
| connector vs ethernet, I wouldn't consider USB-C to be more
| robust than RJ45. YMMV.
| pdpi wrote:
| How often do you unplug RJ45s versus USB-C, though?
| kjs3 wrote:
| I'm not talking about unplugging. Normal use.
| crote wrote:
| The problem is that all of those DC devices don't operate on
| 48V either. The _vast_ majority of chips require a 5V or lower
| input, so with a 48V DC supply you 're still going to need a
| per-device PSU to do DC-DC conversion. In other words: no
| getting rid of power bricks.
|
| Efficiency isn't as straightforward either. You're still being
| fed by 120V/230V AC, so you're going to need some kind of
| centralized rectifier and down converter. It'll need to be
| specced for peak use, but in practice it'll usually operate at
| a fraction of that load - which means it'll have a pretty poor
| efficiency. A per-device PSU can be designed exactly for the
| expected load, which means it'll operate at its peak
| efficiency.
|
| We also don't use 5V DC grids because the wire losses would be
| _horrible_ , so a domestic DC grid should probably operate at
| pretty close to regular AC voltage as well. In practice this
| means the most sensible option would be to have a centralized
| rectifier and a grid operating at whatever voltage it outputs -
| but what would be the point?
|
| As to PoE: I personally really like the idea, but I don't
| believe it'll have a bright future. For its traditional use the
| main issue is that there doesn't seem to be a future for
| twisted-pair beyond 10Gbps. 25GBASE-T might exist as a standard
| on paper, but the hardware never took off due to complete
| disinterest from the datacenter market, and it is too limited
| to be of use in offices and homes. I fully expect that 25G will
| arrive in the home and office as some form of fiber-optic
| interconnect - with fiber+copper hybrid for things like access
| points.
|
| On the other hand, for a lot of IoT applications PoE seems to
| be too complicated and too expensive. It makes sense for things
| like cameras, but individual lights, or things like smoke
| sensors are probably better served in office/industrial
| applications by either a regular AC supply or a local DC one,
| plus something like KNX, X10, CAN, or Modbus for comms: just
| being able to be wired as a bus rather than a star topology is
| already a massive advantage. And for domestic use the whole
| "has a wire" thing is of course a massive drawback - most
| consumers _strongly_ prefer using Wifi over running a dedicated
| wire to every single little doodad.
| matt-p wrote:
| What if all homes had battery storage and or solar? You could
| then simply use it's rectifier as needed or direct 48v from
| the solar panels. That would be even more efficient than
| 230v.
| lillecarl wrote:
| We live on societies, switching from AC to DC because your
| low-power home appliances doesn't need AC makes no sense.
| Home power usage is dominated by heating and cooling not by
| your 45w laptop charger.
|
| DC infrastucture makes sense in highly specialised
| environments.... Like new gigawatt AI farms
| ssl-3 wrote:
| That'd be neat. But there's no standard for voltage for
| home solar: The batteries might be 12, 24, 48v, 60v, or
| even much more. Meanwhile, the panel arrays commonly output
| anything as low as 0V and up to ~600V. There's not much for
| rules and norms here.
|
| Even if we were to standardize a low (<50V) voltage for DC
| distribution within homes, we'd still need ~120/240VAC to
| power big stuff, or we'd instead need even-larger
| conductors (more copper) than we use today to do the same
| work with low voltage.
|
| But, sure -- we can play it out. So let's say we have an
| in-home 48VDC distribution standard and decide that this is
| the path forward and we enshrine it in law.
|
| We need to convert whatever the solar system has available
| to 48VDC. Then, we need to distribute that 48VDC using a
| completely separate network of cabling. Finally, we still
| need to convert 48VDC to whatever it is that devices can
| actually use.
|
| That's not representative of a reduction in steps, or an
| increase in efficiency.
|
| That is instead just an increase in installed
| infrastructure expense, and a decrease in device
| compatibility. It takes what we have, which is simply
| universal (at least within any given geographical area) and
| adds complexity.
|
| And for what? What's the perceived benefit?
| matt-p wrote:
| One of the main problems is conductor size. I wish we could
| access 22AWG copper in cheap and cheerful cat5e/cat6 format
| cable. 24AWG cat5e, sometimes CCA is not great for doing large
| amounts of POE.
| Xcelerate wrote:
| 22AWG Cat6A is actually what I used (cheap it was not
| however).
| ssl-3 wrote:
| It's fun to think about. There's advantages both ways, but I
| think it leans most-heavily towards keeping AC.
|
| 1. One of these is simplicity. With AC, one single home run of
| cabling (eg, Romex) can feed a whole room full of stuff, like a
| bedroom or a living room. At one end of the run is a circuit
| breaker (a fairly simple electromechanical device) and at the
| other end is a series of outlets (which are physically daisy-
| chained, but are functionally just wired in parallel with
| eachother).
|
| Since one single run of cable can feed many devices, it is easy
| to accomplish.
|
| 2. Another advantage is that it is universal. Anything can plug
| into these outlets. Whatever a person brings into the home to
| use, they can plug it into an outlet and it works. It works
| this same way in every home.
|
| 3. And there's quite a lot of power available: A common 20A
| 120v branch circuit cabled up with 12AWG Romex is stated to
| supply up to 16A continuously, or 1920W. For intermittent
| loads, it can supply 20A -- or 2400W. That's tiny by European
| standards, but it's still quite a lot of power. It's plenty to
| run a space heater when Grandma visits and she complains about
| the guest room being cold (even as you start to sweat when you
| cross the threshold to investigate) and a big TV and a whole
| world of table lamps, all at once. And you can plug this stuff
| into any outlets in a room, and it Just Works.
|
| 4. But, sure: Lots of devices want DC, not AC. So there's a
| necessary conversion step that is either integral to the device
| being plugged in, or in the form of the external wall warts we
| all know very well.
|
| So let's compare to power-over-ethernet.
|
| 1. It's also simple, but only tangentially-so. One home-run
| cable per outlet, whether that outlet is used or not, is
| something that can be rationalized as being a simple topology.
| A PoE switch at the head-end instead of a central box with
| circuit breakers is a simple-enough thing to transition to. And
| a lot more individual cables are required, but they're
| relatively small and are generally easier to install.
|
| 2. It's standardized, but it's not universal at all. I've got a
| few PoE widgets around the house, but I'm pretty friggin' weird
| when it comes to what I do with electricity. I can't go to Wal-
| Mart and buy more PoE widgets to use at home, and when people
| visit they aren't bringing PoE adapters to charge their phones
| and other electronics. My computer monitor doesn't have a PoE
| input. I can easily imagine a table lamp or a fan that connects
| to PoE, and also uses it as a network connection for
| automation, and that sounds pretty sweet in ways that tickle my
| automation bones in the most filthy of fashions... but that's
| getting even further into the weeds compared to how regular
| people expect to do regular things.
|
| 3. There isn't a lot of power available. 802.3bt Type 4 is the
| highest spec. And within that spec: While switch ports can
| output up to 100W, a device being powered is limited drawing no
| more than 71.3W. Now, sure, that's 71.3W _per port_ , but in a
| room with 10 ports that's still only ~700W -- at most -- in
| that room. And Grandma's space heater won't run on 71.3W, nor
| her electric blanket. My laptop wants more than this. The list
| of useful, portable things that we casually plug into a wall
| that only draw less than 71.3W is pretty short and most don't
| benefit from the main advantage of PoE, which is a
| _combination_ of [some] power alongside high-speed Ethernet
| data.
|
| 4. We still need wall warts since PoE is nominally ~48VDC. For
| example: Phones use less than 71.3W while charging, but they
| don't run on 48V. That means 120V AC comes in from the grid,
| gets shifted to 48VDC for distribution within the dwelling, and
| then gets shifted yet again to the produce the power (5, 9, 15,
| and 20V are common-enough in USB PD world) that devices
| actually want. That's _more_ lossy conversion steps, not fewer
| -- and we still get to keep the extra conversion (wall warts)
| as punishment for our great ideas. This is not the path towards
| increased energy efficiency.
|
| ---
|
| PoE is great for the things we use it for today. A camera, a
| wireless access point -- you know, fixed-location stuff that
| uses networked data as its _primary function_ and also requires
| power.
|
| Installed PoE light fixtures (like, say, task lights in a
| kitchen) also sounds neat -- unless they die prematurely and no
| PoE replacements are to be found. (Now, you have not just one
| or two problems, but many: The lights aren't working in that
| space and they can't be replaced with a trip to Lowes because
| the Romex that would normally have been installed was
| deliberately deleted from the plan. It could have been a
| 20-minute DIY fix that costs less than $100, but now it
| involves drywall and paint and retrofitting new cabling. Or
| maybe PoE replacements do exist, but it's now 2035 and the new
| ones don't talk the same network protocols as the old ones
| did.)
|
| But there are other upsides: I've got an 8-port PoE-powered
| network switch that works a treat. It's a dandy little thing.
| And it sure would be neat to plug my streaming box in with PoE
| and kill two birds with one cable; I would like that very much.
|
| But most people? Most people don't give a damn about ethernet
| (PoE, or not!) these days, or streaming boxes, and that trend
| is increasing. They just plug their lamp into the regular
| outlet on the wall like they always have, and deal with
| whatever terrible UI is built into their smart TV, and use wifi
| for anything that needs data.
|
| And when they buy a home that is filled with someone else's
| smart infrastucture, their first task (more often than not) is
| to figure out who to call to erase those parts completely and
| put it back to being normal and boring.
| wolvoleo wrote:
| Well they're kinda transitioning back. When I grew up most DCs
| (and telecom facilities) were running on 48V DC. Easy to back up
| with a big room full of lead acid batteries (just keep an eye on
| that hydrogen gas lol)
| tezza wrote:
| They were Thunderstruck?
| Rapzid wrote:
| I somehow made it to middle age without making the connection
| from AC/DC to electricity. Or I never thought about it till now.
| redm wrote:
| I guess we've come full circle. It was just 20 years ago that my
| datacenters gutted DC in favor of AC.
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