[HN Gopher] Linksys WRT54G and WRT54GS power supply (2005)
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Linksys WRT54G and WRT54GS power supply (2005)
Author : peter_d_sherman
Score : 54 points
Date : 2023-11-05 20:49 UTC (2 days ago)
(HTM) web link (kioan.users.uth.gr)
(TXT) w3m dump (kioan.users.uth.gr)
| peter_d_sherman wrote:
| This is an interesting page for several reasons:
|
| First, I think it would be a great idea for any future Single
| Board Computer or Router designer -- to design their product such
| that it will work with _any_ power supply from 5V to 12V
| (assuming that the power supply can provide enough amperes at
| that voltage).
|
| Even better might be to design a SBC or Router such that it works
| with say, a minimum 500 milliamps at 5V -- which should make it
| compatible with just about any consumer power supply out there...
|
| Yes, I know this is wishful thinking for several reasons. But
| let's look at the WRT54G & WRT54GS -- apparently these will work
| a power supply providing any voltage from 5V to 15V -- so long as
| it provides enough amperage at that voltage...
|
| To be able to accomplish this is a great design practice for
| Routers, SBC's, and other small computing devices.
|
| Also interesting: Look at the table of input voltages, supply
| current and watts.
|
| Note that Watts, in general, goes down (not by a lot, and not at
| every voltage, but generally, linearly) as Voltage goes up...
|
| That's an interesting effect...
|
| If the article is correct, then this seems to be the work of the
| "integrated 150kHz _step-down switching regulator_ ".
|
| I think it would be highly interesting (at least, if you are a
| SBC and/or Router manufacturer) to test all available _step-down
| switching regulators_ -- and craft similar tables of input volts,
| amps and watts -- over the regulators ' range of voltages.
| (Octopart anyone? https://octopart.com/)
|
| Which regulator produces the best response over the range of
| voltages it handles, and then, go an extra step -- research and
| discover WHY that is, what are the reasons in Physics -- for the
| phenomenon?
|
| I think that that would be a highly interesting endeavor!
|
| (And of course, I'm also open to any suggestions for webpages for
| people who have already done this, or something like this!)
| mozman wrote:
| You would appreciate this video about constant voltage
| transformers used in vintage computers:
|
| https://youtu.be/X3y7OUERyJg?si=ewtEzh_gGBCAZrRQ
|
| Usagi Electric has a lot of great videos.
| osamagirl69 wrote:
| It sounds like you would enjoy a career in electrical
| engineering. Most undergraduate EE curriculum will offer a
| class (usually both an undergraduate level and a graduate level
| version that covers more advanced typologies) specifically
| dedicated to answering the questions you are asking.
|
| Lucky for you the course notes are available for many of them.
| For example 6.334 from MIT
| https://ocw.mit.edu/courses/6-334-power-electronics-spring-2...
| Goz3rr wrote:
| > Note that Watts, in general, goes down (not by a lot, and not
| at every voltage, but generally, linearly) as Voltage goes
| up...
|
| I would say it flattens out pretty quickly and doesn't keep
| going linearly. This probably has to do with the fact that the
| device was designed to be powered from 12V so the supporting
| components of the power supply would have been chosen to
| maximize efficiency around that input voltage.
|
| EDIT: I was curious and had a WRT54G v2.2 laying around (unlike
| the 1.0 used by OP), which results in this graph:
| https://i.imgur.com/CBNTtRI.png The lower power usage can
| probably be explained by my later revision having less LEDs and
| more integrated chips instead of several discrete ones.
| Scoundreller wrote:
| This "higher input voltage is more efficient" can also happen
| with bridge/protection diodes. (E.g. devices that accept AC or
| DC, or any polarity of DC, or at least safely refuse to
| function if you plug in a barrel connector with the wrong
| polarity)
|
| They'll cause a fixed voltage drop, so the higher the voltage
| you put in, the lower the proportion of your power you lose.
|
| 240V computer power supplies are a bit more efficient than 120V
| ones because of this.
| quietpain wrote:
| First, I think it would be a great idea for any future Single
| Board Computer or Router designer -- to design their product
| such that it will work with any power supply from 5V to 12V
| (assuming that the power supply can provide enough amperes at
| that voltage).
|
| Devices that do that have been available for 10+ years, e.g.
| the OKI series:
| https://www.mouser.com/datasheet/2/281/oki-78sr-56393.pdf
|
| It's about the size of your thumbnail, costs around $5 and
| takes input voltage up to 36V
|
| These are my go to devices when I'm installing something in an
| old device, e.g. adding bluetooth to an old amplifier.
|
| edit: handling more power would require some more space but
| isn't exactly rocket science.
| Rediscover wrote:
| > ...Router designer ... to design their product such that it
| will work with any power supply from 5V to 12V...
|
| I am one of those who often makes purchase decisions around the
| internal power circuitry.
|
| I'm not at my lab desk at the moment (so I cannot report on
| that stuff), but I'm dragging around an old laptop, a small SBC
| (used as a general-purpose computer) and a monitor that I was
| employing earlier in cramped quarters for 40 minutes or so. The
| laptop is happy with 11.5V but doesn't have problems with
| 11-18V (9V 600mA will still charge the battery, _slowly_ ,
| during very mild use). The SBC has an NB679 buck converter so
| it's good for 5.5-28V. The monitor (2200 nits baby!) will
| accept 7-24V. These are older kit I use for crawling around
| with, but most of my "normal" equipment likewise has large
| input tolerances.
|
| Non-normal equipment (used for areas at home where tool
| loss/damage may occur) mentioned: OLPC XO-1 (great screen,
| kinda tough, freakin' old), FriendlyElec NanoPC-T4 SBC,
| FeelGood P7 field monitor (compact with a thick aluminum
| chassis).
| superkuh wrote:
| Yep, I did manually injected PoE on the extra ethernet pairs and
| soldered directly to the wrt54g board to put my router 70ft up in
| the pine tree next to my house. I powered it with 13.8v from a
| ham radio psu and it worked great. It was almost certainly less
| than 12v after the voltage drop from the run. I never did measure
| though, it just worked (for years).
| mozman wrote:
| How did you weatherproof it with antenna penetrations?
| superkuh wrote:
| I put everything in an oven pan then used a LCD screen
| diffusor panel for the top. I drilled holes in the side of
| the pan and sealed them with caulk. I did eventually get some
| water ingress from daily pressure/temp changes + humidity and
| significant rusting of the bottom of the pan but the elevated
| wrt54g was operational (if a bit nasty looking) when I took
| it out after 3 years. If I did it again I'd add some
| weep/drainage holes to mitigate build up.
|
| http://a.superkuh.com/wrt54g-in-oven-pan-with-caulk.jpg
| Scoundreller wrote:
| I'm surprised the zip ties survived in the sun like that
| without getting too brittle.
| rabbitofdeath wrote:
| Making sure you get UV resistant zip ties is key.
| phero_cnstrcts wrote:
| > manually injected PoE on the extra ethernet pairs and
| soldered directly to the wrt54g board
|
| Is there a guide for that somewhere?
| squarefoot wrote:
| A search for "PoE injector schematic" returns some
| interesting results.
| EvanAnderson wrote:
| If you're looking to connect a DC-powered device to a
| standards-based power-over-Ethernet switch without making any
| device modifications look up "PoE splitters". They're really,
| really handy devices. You can get them with USB connections
| and barrel plugs. I've gotten a lot of mileage out of them
| over the years.
| Scoundreller wrote:
| As the article goes into, it drops everything down to 5V (or
| less) on the board. So as long as you're getting like 7V
| (possibly as low as 4.75V per the article) to the board, you're
| good.
| Scoundreller wrote:
| As devices like home fridges move towards "inverter drive" with
| switch mode power supplies, I wonder how low of a voltage they
| could still run off. And if they'd happily accept 48VDC and still
| function.
|
| Saw a teardown/repair of a big home flatscreen TV and while the
| label on the outside said "120VAC", the power supply inside said
| 120/240V, so it was the same internals worldwide, but labelled
| differently to discourage gray-market imports.
| kube-system wrote:
| It could have just been that one team labeled the housing
| according to the requirements, and another team built the
| internals to meet (or exceed) the requirements.
| Goz3rr wrote:
| Or the power supply is sourced from multiple vendors, and
| other units might not have the same range
| woleium wrote:
| Or the power units were from a run that ended up as
| defective at the higher voltage
| Scoundreller wrote:
| Going to be no bueno if donor boards end up on the
| secondary market.
|
| But now that I think about it, it's possible they're
| fitted with different replaceable fuses (half the
| amperage in 240v areas).
| mschuster91 wrote:
| > As devices like home fridges move towards "inverter drive"
| with switch mode power supplies, I wonder how low of a voltage
| they could still run off. And if they'd happily accept 48VDC
| and still function.
|
| The technical side should continue to work until you reach the
| lower limit of what the bootstrap circuitry can handle.
|
| The problem will be the amperages required... say, a fridge.
| Its motor will run at ~200 watts, which means 1A at 230V. No
| biggie. But if you're going down to 48V, the high-voltage side
| will now run 4A, and more the lower you go on voltage - and
| that's without taking peak inrush currents into account which
| can easily go to 10A@230V (or 40A@48V) for a few split seconds.
| If your current source or the wiring can't hold that, you'll
| likely run into serious issues.
| sokoloff wrote:
| I thought one major advantage of inverter drives was the
| well-managed starting currents. This is a noise/vibration
| advantage but also an electrical win.
| hinkley wrote:
| But a wire pulling 2 amps at 3.3 volts experiences very
| different physics than a wire pulling .6 amps at 12 volts.
| quickthrowman wrote:
| Inrush current is much less of an issue with a VFD/inverter
| driven motor then a motor controlled by a basic DOL motor
| starter. ABB claims that the inrush current of their VFDs is
| 100-150% of the motor FLA, which lines up nicely with the NEC
| rule to size motor conductors at 125% of the FLA of the
| motor.
|
| https://library.e.abb.com/public/71d5526a71b34360bb3a258c950.
| ..
| hinkley wrote:
| I recall someone stating rather authoritatively that they were
| confident that the WRT54G could comfortably run directly off of
| automotive "12 volt" DC power, which in practice can go up to
| 16 volts due to the alternator.
|
| This person has a thesis that it can go up to 20 volts (which
| is 80% of the rating of one of the capacitors)
| Scoundreller wrote:
| Which could be user upgradeable with a snip and a soldering
| iron.
|
| It's just a smoothening capacitor, so higher voltage rating
| is the critical part and can probably get away with non-exact
| muF capacity.
|
| Possibly removable if you have a lead acid or lithium-ion
| battery capable of providing lots of current when needed and
| cleanly.
| jauntywundrkind wrote:
| Now that source/supply and sink/drain/device are usb-c, it seems
| like this kind of flexibility would be possible for a huge number
| of systems.
|
| It'd be interesting for systems to expose their efficiency
| curves, to make these kind of decisions optimally. Maybe your
| charger is much more efficient at 20v that the power efficient
| optimal solution is to pipe 20V in, even at low power modes.
| There's all kinds of optimization problems we could tweak, if
| this sort of efficiency data were visible.
| tpolzer wrote:
| Ideally with PPS, your device can actually just ask exactly for
| the regulated voltage it needs on USB-C.
|
| Most modern smartphones can use that to charge their batteries
| more efficiently/with less heating of the phone.
| jauntywundrkind wrote:
| Sure but that doesn't take into account charger efficiency.
|
| Something designed to output 5V-48V might be quite
| inefficient at generating an asked for 6.65V, perhaps.
| Optimizing just for the device might be missing gobs of
| energy efficiency that could easily be found with a little
| testing & discovery.
|
| There's decent odds that a good PPS implementation on the
| device - one that can directly connect the supply and battery
| without having to do intermediary conversions - is the most
| efficient option. PPS probably _is_ the best choice. But it
| 's not guaranteed. And particularly as we create higher power
| higher voltage capable chargers, their optimization point
| might be tuned to much bigger outputs (where they will
| absolutely require that efficiency to keep cool enough under
| load). Losses from running your charger sub-optimally could
| dwarf losses from the device receiving power sub-optimally
| for it.
|
| The point seems to hold: we need data to know what the best
| option to do is. This submission showed one way of DIY'ing
| that data, but devices could also do better jobs self-
| reporting, which would let everyone tune better.
| mschuster91 wrote:
| > That means that the lower limit of the supply voltage is about
| 5V but the upper limit is much less than 40V. That's because the
| input capacitor is rated at 25V, so I would not suggest running
| it on more than 20V.
|
| Even that will stretch it without rework. The higher the voltage
| difference, the higher the heat losses - at the minimum you'll
| need a heatsink, at higher voltages I'd even go for active
| ventilation.
| jhenkens wrote:
| If the total power consumption at the supply is the same or
| lower, how is the voltage regulation circuitry generating more
| heat?
| mschuster91 wrote:
| The problem is the voltage drop. The bigger voltage
| difference it has to handle, the hotter it gets as its the
| loss from "internal loss current x voltage drop" is converted
| into hat.
| jhenkens wrote:
| The heat has to come from the input power though. If I'm
| pumping 5W at 12V, or 5W at 20V into the device, with it
| idling, presumably the output from the devices voltage
| regulator circuit is the same voltage, and the downstream
| components are consuming the same wattage (let's call it 1A
| at 3.3V downstream, so 3.3W), the both the 12V and the 20V
| input would have 1.7W of heat-loss. The article shows that
| as voltage goes up, power actually drops, which would imply
| that it is producing less heat.
| onetwentythree wrote:
| That only applies to linear regulators.
|
| The router on this page uses a switching regulator.
| Switching regulators have a relatively constant power draw
| over the entire input voltage range.
| tonyarkles wrote:
| Yeah, I think they've mixed up linear regulators and buck
| converters. Buck converters are often more efficient with a
| larger voltage drop because the switch can run with a lower
| duty cycle.
| jhenkens wrote:
| Thanks, I never knew why. All I knew is whenever I need a
| buck converter in my DIY, novice PCBs, I just toss in an
| off-the-shelf preassembled one, with a small LDO on my
| actual PCB to drop the last bit and smooth it out.
| buildsjets wrote:
| Apple made a big deal about the switching-mode power supply that
| was used in the Apple ][ computers, although this author thinks
| that they were over-hyping their contributions to the technology
| a bit.
|
| http://www.righto.com/2012/02/apple-didnt-revolutionize-powe...
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(page generated 2023-11-07 23:00 UTC)