[HN Gopher] The cases of consumer-grade routers on puny power su...
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The cases of consumer-grade routers on puny power supplies
Author : fanf2
Score : 50 points
Date : 2025-01-06 18:42 UTC (3 days ago)
(HTM) web link (blog.apnic.net)
(TXT) w3m dump (blog.apnic.net)
| gruez wrote:
| >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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| timewizard wrote:
| There's nothing special about the transformer in SMPS
| other than it's size which is due to the high frequency.
|
| The other problem they create, then, is high frequency
| noise which must be filtered out. Some cheaper adapters
| just dump the noise back into the mains and cause
| problems for _other_ devices.
|
| Come to think of it there's a decent chance it's a
| /different/ adapter somewhere on his system that's
| causing the problem and not the size or capacity of the
| products native adapter.
| krunck wrote:
| There are server power supplies that won't work on non-
| sinusoidal power sources. (read: cheap UPSs) I learned that the
| hard way.
| Animats wrote:
| 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.
|
| [1] https://hackaday.com/tag/wall-wart/
| giantrobot wrote:
| 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 wrote:
| Label maker, apply to power supply!
| giantrobot wrote:
| This has been my exact strategy. I've finally got about
| half my box-o-wallwarts labeled for their associated
| device.
| LeifCarrotson wrote:
| This is the opposite of my strategy: each wall wart in my
| box gets a legible label with voltage and ampacity. Eg 9V
| 200mA, 12V 500mA, etc. Each device gets a corresponding
| legible label with its required voltage and maximum
| current.
|
| Then it's just a matter of picking out one that's
| adequate for the selected device, it's a many-to-many
| mapping with lots of valid solutions, not one-to-one.
| devwastaken wrote:
| 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.
| ssl-3 wrote:
| 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.
| causality0 wrote:
| 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.
| ajuc wrote:
| 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 wrote:
| I used to run my mother's vacuum cleaner plugged into the same
| outlet as my C64 to keep it from crashing.
| ianhowson wrote:
| 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.
| Panzer04 wrote:
| 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.
| PaulDavisThe1st wrote:
| 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.
| kllrnohj wrote:
| 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 wrote:
| > 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 wrote:
| 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.
| gazchop wrote:
| 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.
| timewizard wrote:
| > 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.
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(page generated 2025-01-09 23:00 UTC)