The cases of consumer-grade routers on puny power supplies
47 comments
·January 6, 2025ianhowson
Panzer04
Generic issues like brownouts and crashes I can believe as a power fault. Slowdowns? Not likely.
Possibly he's not describing the problems right. I can certainly believe a shitty enough power supply would cause problems.
pinkorchid
That actually happened at my job a few years ago, where some extra power draw off a power supply that was also feeding a PC would slow down the code running there. It does sound crazy...
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Waterluvian
I’m super fascinated by the rare occasion that digital things degrade in an analog fashion. Usually they just work or don’t.
PaulDavisThe1st
Yeah, I've lost two modem/routers to power outage incidents, despite them being on a reasonable quality surge protector.
But that was an all-or-nothing failure mode in which they would power up but never do anything else. Performance changes is a claim that requires much stronger evidence.
mindslight
When I hooked a Raspberry Pi (model B maybe?) up to an analog input on my Marantz NR1605, the UI of the receiver got noticeably laggier until it was barely responsive. Disconnecting made the UI perk back up. I noticed the Pi had a 2.5V DC bias on its audio out. I didn't investigate further.
As for the article, I'm left with more questions. Surely the solar inverter wasn't running all the time in series, like a double conversion UPS, right? So how how would the mains waveform have been significantly affected in normal operation?
Also those scope traces, what's the scale? Are we talking 100mV dip, or a 1V dip? And is that a storage scope, or is that one cycle of the supply's ongoing ripple? And the complete lack of any dip on the "fixed" trace with extra capacitance makes me wonder if they even got the triggering right.
CoffeeOnWrite
I think the inverter is always running in between the batteries and the AC outlets. It's a dedicated "solar circuit".
I have questions. What's the point of a dedicated solar circuit? They are leasing from their "local lines company". If the lines company is in the leasing business, this system must be grid-tied right? Why the dedicated solar circuit?
Also, is it common for full sine wave inverters to produce power less clean than the grid? Maybe when the batteries are low? Curious.
jen729w
My neighbour's internet was terrible last year. He replaced a bunch of stuff, and went as far as switching ISPs to my recommended provider. Nothing worked.
Finally a savvy helpdesk person had him move his ADSL router. I believe he moved it off a cheap power board and plugged it directly in to the wall.
All problems immediately solved.
PaulHoule
ADSL is particular sensitive to electronic noise. I'm afraid to set up my HF ham radio again.
kllrnohj
A fancy modern turbo'ing CPU which has power availability feedback loops might just slow down in this scenario, but I don't think anyone has put anything remotely that fancy into a low power SoC that these routers were using.
So yeah, seems unlikely the only impact would be a sluggish dashboard. Maybe the device was churning on error re-transmissions from the brownout? Like the CPU itself was OK but the ethernet ports weren't?
ianhowson
> Maybe the device was churning on error re-transmissions from the brownout
I think this is more likely. Two different routers impacted. Crappy grounding or induced noise causing high BER on the links.
outworlder
How fancy do we really have to get? A Raspberry Pi can detect an inadequate power supply and slow down.
Granted, cheap consumer devices are much simpler than that, but it's still something that can be added to the SoC.
dustyventure
I think the original Broadcom chips were overstock in the normal market because they were somewhat a nuisance of unnecessary checkboxes that would reward you with further testing/diagnostic complications in return for paying too much..
gazchop
I agree that you'd probably see crashes but it still could be power supply related. Crappy SMPS designs do tend to shovel some noise from the primary into the secondary side as well as adding their own. And there's a lot of noise generally coming from an inverter as specified. It might just be adding noise to the line and crapping on the SnR occasionally. ADSL is quite robust but with noise it does slow down horribly if you bend it hard. I used to be able to slow my line down keying on my amateur radio transmitter back in the day.
About the best thing they did was adding a choke on it.
On top of that, it's a crappy 40MHz analogue scope. You're not going to see anything useful.
gruez
>Clearly, the router is pulling more current during the dip than the power supply on my solar circuit can supply.
>[...]
>Ideally, we’d want manufacturers to put capacitance to that effect into their router power supplies or at least routers. But we realise that capacitors cost a few cents each and aren’t really required on stable grid supplies. And manufacturing costs matter.
Weird this was being seemingly blamed on "puny power supplies", and that "ideally" manufacturers should be overspecing their power supplies to accommodate his use case. Does he also think manufacturers should "ideally" add a battery to routers on the off chance that there's a transient blackout?
More to the point, he supposedly has a "4500W peak solar sinewave inverter", and his router probably consumes no more than 50W. That 50W is unlikely to cause issues with such a system, and even if it was the straw that broke the camel's back, it's weird to blame it on the router, rather than the inverter or the entire system. If you had a take-home salary of $10k, blew it all on gambling, then your card got declined on a starbucks purchase, you wouldn't characterize this as "my coffee habit was using more money than my income can supply".
digitalPhonix
The 50W load (if that) isn’t the problem - a lot of cheap power supplies assume a perfect sinusoid which you get from a spinning mechanical source of electricity.
The inverter probably only does a few step approximation of a sin wave which is fine for most things, but clearly not for this power supply which browns out (I’m guessing during an extended period of 0v on the stair step sin approximation).
Whether your average power supply should be tolerant is unclear, but if it’s the only device playing up it’s clearly less tolerant of imperfect power than everything else.
wildzzz
The wallwart for the router is going to be a dead simple design that doesn't in the least bit care about how dirty the sine wave is. It goes into a step-down transformer (12VAC usually), into a bridge rectifier (now 12VDC), add some decoupling caps to smooth out the 12V. Inside the router, there will be LDOs that bring that voltage down to something usable along with more decoupling caps to filter the input and output of the LDO. LDOs have high ripple rejection especially at low frequencies so they can take on pretty dirty voltages.
Unless that little dip on the supply is constantly happening, I highly doubt that's causing any of the issues. That dip could be from in-rush current or from the router powering up, both of which would be happening before any data transfer. It means nothing without any sort of voltage or time scale.
alright2565
There's no way a router in 2024 is using a big iron transformer. They're too expensive.
It'll be a switch mode power supply, where the power is rectified, converted to high-frequency AC (50-200 kHz), then sent through a certain specialized transformer.
krunck
There are server power supplies that won't work on non-sinusoidal power sources. (read: cheap UPSs) I learned that the hard way.
namibj
Use one that has the "240VDC (China only)" rating, and feed them proper DC.
Or get the modern western ~300V DC input ones, there's no good (technical) reason to feed AC from a non-grid-tie inverter to a SMPS-only circuit.
The DC can be quite passive, just switched in via a relay and anti-reverse-current-diode together with bridge-rectified mains, she otherwise just bare battery bank voltage There's a reason modern data centers use that style of setup (except with a central power factor correcting rectifier, not a plain bridge rectifier, and often hanging the batteries on it directly using controlled rectifier output voltage to control battery charging).
Animats
Huh. Is that line on the scope a one-time glitch at power up, or does it happen on every cycle?
"Rummaging through my old parts box unearthed a power supply that was a bit more powerful than the one that came with the router, and even fit the connector." Is he describing a "wall wart" type power supply? A picture would help. A teardown would help more. There are large numbers of really crappy wall-powered DC supplies available, mostly from China.[1]
Look for a UL approval marking and a UL approval number. That indicates at least some attention to quality. UL is mostly concerned about fire safety, but their basic test for power supplies includes connecting it to a load box at the power supply's maximum rating, then running it for a while to see if it overheats. This catches power supplies with exaggerated ratings.
Avoid no-name power supplies. This is a well-known headache.
ssl-3
UL tests electrical products for safety.
It isn't a mark of quality, or of fitness for purpose.
It does mean that the device(s) submitted for testing are unlikely to burn your house down, though.
giantrobot
I've found that a lot of devices anymore just pack in those no-name power supplies. Many things don't even ship with branded PSUs now. It makes sorting my box-o-wallwarts a giant pain in the ass.
Edit: don't repeat myself
themaninthedark
Label maker, apply to power supply!
giantrobot
This has been my exact strategy. I've finally got about half my box-o-wallwarts labeled for their associated device.
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devwastaken
Listing labs are a known scam. you pay them significant amounts to curb what result you want. then you change the components to cheaper quality and sell those.
The correct and effective means to have safe and correct products is to monetarily and criminally punish corps that produce faulty goods.
friend_Fernando
An even better fix for this category of problems is DC distribution at the homelab scale. I've replaced most of my 5V and 12V wall warts with a PC PSU. A number of transient issues that used to affect some of the gear disappeared.
baobun
Similarly: I thought I had some bad workstation hardware (brand-name mobo and PSU), seeing severe memory corruption issues. After putting it behind a UPS (only after losing a zpool from it), it's all clean.
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causality0
So he repeatedly feeds dirty power into consumer routers and is surprised when they don't function correctly. Then he writes an article complaining about it while being careful to exclude any relevant facts like the models of router and power supply or any actual measurements from his oscilloscope. Gold star writing this is.
timewizard
> But we realise that capacitors cost a few cents each and aren’t really required on stable grid supplies.
The type that can do this also fail at a rate that depends on temperature. Which is why they shouldn't use them internally. If you truly need to condition your power than you need to do it separately as almost no one shares in this problem and would not be benefited by adding these degradable parts.
ajuc
Some things never change.
I remember waking up early on Saturdays in 90s to load some game from tape on my C64 before the neighbor starts his sawmill. Couldn't load anything when it was running :)
mmcgaha
I used to run my mother's vacuum cleaner plugged into the same outlet as my C64 to keep it from crashing.
null
Irrelevant.
1. Downstream of the mains power supply are DC-DC converters that run the router hardware. Those contain the filters and capacitance you think you're fixing. Nothing in that router actually cares about mains power quality. They absolutely do not care about perfect sinusoids.
2. If you were seeing insufficient power to the router, you would observe crashes and faults -- not slowdowns.
3. Two different routers showed the same behavior, which suggests that the fault lies outside the router+power supply and more to do with something common (e.g. network, laptop).
The dip shows a reduction in voltage, and a larger one than I would like, but without a scale on either time or voltage, it's difficult to guess if it actually matters. I would suspect not, since the device does boot successfully. Again, the voltage doesn't matter, since the router runs off its internal DC-DC supplies, not the external power supply.
I'm happy that the capacitor and new supply has fixed the issue, but I'm unconvinced by the explanation. Check grounding between inverter and laptop.