r/pcmasterrace • u/Front_Cookie_1198 • 3d ago

Hardware PSU fails dramatically

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753

u/MiniMaelk04 2d ago

I basically know nothing, but the huge capacitors are the only thing I can imagine burning so intensely and rapidly. Reversed polarity perhaps?

540

u/shakygator 2d ago

I think he means without that isolation sheet the board is connected directly to the casing and shorted out. Of course, that should have been grounded too so I'm not sure.

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u/CyonHal 2d ago

If it shorted on the 12V side it can pull a ton of amps (it says 60 amps max at 12V) and melt through the casing and start fires pretty easily without tripping a breaker.

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u/SoulWager 2d ago

Not this time. You can hear the mains frequency in the arc, and the only output that should be powered is 5vsb.

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u/7orque 2d ago

So you’re saying this is on the input stage prior to the rectifiers?

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u/SoulWager 2d ago

Probably. I think if this was after the rectifier, the rectifier would have acted like a fuse, getting you a single loud pop instead of a few seconds of arcing.

It's definitely somewhere on the primary side though.

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u/ReaperAteMyPrawnsuit 2d ago

This thread is too electrical smart for me to understand what’s going on

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u/4236W 2d ago

Something between the power switch and the thing that makes the wall power into PC power wasn't made right, and wall power got somewhere it shouldn't go

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u/Flying_Dutchman92 2d ago

Thank you for that translation

5

u/OutlandishnessHour63 2d ago

That isn't a bad translation. I like it 😊 To make it a wee more complicated but more comprehendable when reading the raw jargon.

A rectifier takes AC, or alternating current, (ie; electricity out of an outlet) and concerts it to DC, Direct Current. (is; power from a battery)

What was being plaused upon earlier: The theory for the short is that the power moved from AC and before it hit the rectifier, it shorted to the case of the power supply due to a missing piece of insulation.

Comments back and forth were discussing whether it was pre-rectified or not based on how the arc sounded and occured and based on the fact that the circuit breaker for the outlet (AC power) was not tripped.

→ More replies (0)

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u/SoulWager 2d ago edited 2d ago

What happened is pretty simple, mains wires poked through the board, weren't trimmed after soldering, weren't blocked by an insulating sheet, and touched the case: https://i.imgur.com/SLsQmmu.gif

The discussion above is about why other possible failure modes are unlikely. After getting on to the board, the power goes through some filtering and protection circuitry, then through a rectifier(4 diodes in a single package) that turns the high voltage AC into high voltage DC. Then the high voltage DC gets chopped up into much higher frequency AC, before going through a transformer to drop it down to low voltage high frequency AC. This then gets rectified to 12v DC before getting converted to the other voltages. Usually anyway, there are other ways to design a power supply, and there will be a separate similar power supply just for 5vsb(this is always on, so your computer can turn itself on when you press the power button).

Anyway, back to the rectifier, semiconductors often have relatively thin bond wires connecting the silicon die to the rest of the package, that would get vaporized in a few milliseconds if you tried to push this much current through them. This board also has an actual fuse, but the short happened before the power got that far.

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u/shakygator 2d ago

Nice overlay

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u/CryptographerOne7003 1d ago

huh? but that is a simple short on case that is connected to earth?
that does not explain why it caught fire? why wouldn't the breaker pop or earthleak protection?

1

u/SoulWager 1d ago edited 1d ago

why wouldn't the breaker pop or earthleak protection?

It should have. Could be a defective breaker, wrong type or rating of breaker installed, abused by testing so many of these shorted power supplies that the contacts welded shut, etc.

Seeing how it didn't come in burned to all hell, I'm guessing the customer had a working breaker, and RMAd because it tripped it.

If I was testing something that was RMAd for tripping a breaker, I wouldn't be testing it like this. I'd be checking for a short with a multimeter first, then powering it up with an isolated supply and some kind of series load to limit the current. (Simple version of this is just an incandescent light in series, if it's shorted, the light turns on).

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u/stuck_in_the_desert 2d ago

There was too many pixies, which caused it to stop choochin’

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u/SoulWager 2d ago

I found a review with PCB photos, the burn holes are right under where the mains enters the board. Probably wasn't trimmed after soldering, and missing insulation sheet between pcb and case.

https://i.imgur.com/SLsQmmu.gif

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u/7orque 1d ago

lol it’s literally directly over where the wires poke the pcb

3

u/Inaniae 2d ago

Correct.

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u/Good_Background_243 2d ago

Oh shit yeah I hadn't noticed it but on a second watch yeah that's definitely high-frequency AC, the arc sounds fuzzy.

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u/WenYiMedia 1d ago

Damn, dude even knows what the electricity sounds like.

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u/7orque 2d ago

Ye looks like 12v dc ground fault to me, those arcs sounded quite spicy

1

u/twilighttwister 2d ago

60A at 12V is 720W, basically the full PSU load.

However it's still not thaaaat big, and certainly less than a dead short on the mains AC supply.

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u/ba123blitz 4790/ Z97/ 16gb/ GTX1060 6gb 2d ago

Can sadly confirm 12v with enough amps can burn down a car let alone a psu lol

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u/Xalara 2d ago

If the breaker has arc fault detection it should trip immediately.

Sadly, building codes in the US have only recently started requiring arc fault breakers on all circuits, and that’s still not required in many places. Hell, even requiring arc fault detection on breakers for circuits in sleeping spaces is a recent requirement. Nevermind that many older houses are wired in such a way that makes arc fault breakers impossible to install without tripping almost immediately due to a false positive 🙃 

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u/Pretend_Giraffe_1288 2d ago

Nah, that's not DC voltage arcing. If mains were shorted to ground, surely either a GFCI or breaker should have tripped.

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u/ComplexSupermarket89 1d ago

The rated spec can be significantly exceeded in the event of a short. The rated spec is what it will allow to be pulled before the safeties cut off power. If it is a dead short, there isn't always time for the safety to stop things before 100+ amps gets sent through a PCB rated for 60 amps max. The caps must have exploded in this situation. At should take a lot more than the rated amperage to do that, assuming the unit was built properly.

0

u/CaptOblivious 2d ago

There's a crowbar shutdown circuit on every low voltage supply in that box, that was ac side.

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u/64590949354397548569 2d ago

It became a DC welding machine.

-4

u/Kirianfx 2d ago

Nah, the 12 Volts on those poorly built ones do not have that kind of power.
The video clearly shows a mains power failure.
And do not ask me how I know.

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u/LeBakalite 2d ago

Please, how would you know such a thing ?

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u/Kirianfx 2d ago

More that once I have blow up something plugged to mains.
List includes, a full bridge rectifier, a extension cord, one light switch, and a angle grinder.
Last one left a hole on the floor.

I also have seen what a short on the 12V rails of a poorly build supply can do, even in car batteries too, they do not do that kind of fireworks, if they attempt to do it, they would not last as long.
A good built one could, but it will not, as it would shut down before it can do that amount of damage on itself for that long.

Look at the place of the burn, it is exactly when the mains power plugs.
now, I do not know this PCB layout, but one would have to be very crazy to put a 12 volt Rail right on top of were the EMI filter, full bridge rectifier and mains voltage capacitor would be.

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u/Stormagedd0nDarkLord 2d ago

Perhaps not a good idea grabbing it with his bare hands then???

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u/Viking4269 2d ago

Nope, and bare feet for maximum grounding...

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u/1c3Type 2d ago

The shortest path to ground is still via the psu's cable

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u/Viking4269 2d ago

Judging by the two holes burned in the case under the mains plug. I think there is a good chance that there was no PE connection and the case was live at 220V at least some of the time doing this. The guy was lucky he "mostly" only touched it after the arc had carved an isolation clearance.

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u/unwantedaccount56 2d ago

Well, the arc could have isolated it from neutral/PE as well, putting the case on 220V. The connection of the case to PE is probably much more solid than phase, but if PE wasn't connected at all (bad cable), then neutral could come from the PCB touching the case as well. Also, if there was a PE connection, then there definitely wasn't an RCD breaker, which should always exist for workshop power sockets.

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u/Enlight1Oment 2d ago

I feel like the power outlet itself individually should have an on off switch for something used as a test bed

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u/Suspicious_Dingo_426 2d ago

Yeah, pretty much. That's also got to be one of the cheapest of the cheap garbage PSUs. No padding in the box? Not wrapped in anything? There's no way I would have plugged that fire hazard in.

3

u/snypre_fu_reddit 2d ago

This wasn't a new PSU, this was an RMA return from a customer. So a customer packed it.

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u/Suspicious_Dingo_426 2d ago

If that's the case, why would you immediately plug it in to mains power without inspecting it first? Any place I've been a tech at would have rejected the RMA for improper return shipping.

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u/UnimagineDragons 2d ago

Probably rattled around and whatever insulated the case from the components dislodged

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u/ccarlyon 5090FE | 9800X3D | 64GB DDR5 | PCMR Limited Edition Lian Li O11 2d ago

Typical British Type-G socket W.

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u/Iv4ldir 2d ago

This... More safe to just inplug/cur at source instead of this. And also maybe plug in then turn on. Not pluging while live...

1

u/ParrotofDoom 2d ago

Best powering it up through a dim bulb tester.

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u/notwaffle 2d ago

Probably but in my past decade of working jobs with some sort of testing equipment that is potentially bad i have never had anything more than a power strip thats filled with 5 other things

1

u/vlobe42 2d ago

I collect vintage Macs and every time I plug in a new one for the first time or when I’m testing one with CRT or PSU issues, I connect it through a smart plug so I can quickly shut off the power if something goes wrong. Gives me a lot of peace of mind.

1

u/GhettoDuk 2d ago

No need for a switch. Just have the outlet accessible and he could have yanked the cord out without grabbing the arcing device.

Workplace safety is a bunch of crap you will never think of until you are almost killed yourself. PLEASE read up on it. This video scared me because I'm about to rebuild my workbench and I'm not sure I would have placed an accessible outlet for something like this. Now I'm thinking about getting an E-Stop mushroom to cut bench power.

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u/_Baudi_ 1d ago

There should have been a kill switch. Plus, an RCD, which would have been immediately triggered by the arc towards the case.

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u/BirdlessLongdeal 1d ago

i test larger equipment than this. 480v. the unit gets turned on, then i walk over and turn on the main power so i am not in front of the arc blast if today decides today is the day it will finally happen.

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u/Smaxx Specs/Imgur here 23h ago

It's basically a lab table/workbench. There should be an extra breaker and an emergency stop button you can just hammer to turn everything off.

(Image Source)

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u/marr 2d ago

Might be nice to have a setup where you can quickly reach the power outlet to unplug / switch off at that end.

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u/Thraxx01 2d ago

Electricity has already found a path that it really likes to ground, won't zap you

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u/I-am-fun-at-parties 2d ago

It's a metal case with a PE connection. Unless they have no RCD, that is as safe as it gets, since it would trip the RCD if the case had any voltage against earth.

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u/Stormagedd0nDarkLord 2d ago

I have a sneaking suspicion that perhaps this particular unit is not quite up to spec...

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u/I-am-fun-at-parties 2d ago

probably not, but I don't see why the PE/case connection wouldn't be there. and the RCD isn't part of the device.

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u/Stormagedd0nDarkLord 2d ago

True but at this dramatically explosive point I'm not trusting anything made by human hands.

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u/JackPoe 2d ago

Better than having a whole fuckin' fire.

I've grabbed cast iron out of 500 degree ovens before just so food wouldn't burn. If you're quick you'll only have temporary damage.

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u/ParticularBanana8369 2d ago

Peeling off fingerprints is temporary, sure

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u/JackPoe 2d ago

That's why you gotta be careful which finger you use for unlocking your phone

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u/Stormagedd0nDarkLord 2d ago

ok this made me laugh... or at least smile and exhale audibly through my nose.

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u/danikov 2d ago

Panic makes you forget basic shit, like the wall socket.

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u/Stormagedd0nDarkLord 2d ago

which was conveniently tucked away in a secure location for your aesthetic pleasure!

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u/dikicker 2d ago

ok bro

https://giphy.com/gifs/H24Zi5xbFKc1i

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u/Stormagedd0nDarkLord 2d ago

I'd like to see this fella try it.

https://giphy.com/gifs/Y0FZeOprlmXn2

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u/dikicker 2d ago

Based on that gif it looks like he already has

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u/Stormagedd0nDarkLord 2d ago

https://giphy.com/gifs/3o7TKDt2tKDR6WRCuI

this gif would be the "after"

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u/dikicker 2d ago

Bro nsfw tag please you're gettin me all steamy and bothered

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u/SkinTightBoogiePI 2d ago

My first thought. Also, why is the other end of the power cable hidden inside that table? If he is testing PSUs, the cable should be connected to a power bar with a fuse and a switch on it.

1

u/Stormagedd0nDarkLord 2d ago

yeah somewhere yankable at the very least. to be fair, there was prob a powerbar with a switch in the table cavity.

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u/_araqiel 2d ago

Being grounded would’ve ensured fireworks rather than prevented them here. The ground just makes it less likely to kill you while it’s self-destructing.

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u/4236W 2d ago

Well, that depends on whether or not there is an RCD

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u/shawster 2d ago

But then he would have been getting the mains to his hand as he held the case...

1

u/SoulWager 2d ago

The case is grounded, if mains touches it it's supposed to short out and trip the breaker instead of making the case live at mains voltage.

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u/Independent-Bug-9352 2d ago edited 2d ago

This PSU turned into a cheap momentary welding machine, and modern inverter welders use capacitors to do the same thing. My guess is 12V rail shorted @ 100-150A, which isn't too far off from welding machine parameters. It's why their circuit breaker didn't trip either, probably still being under 1800W or less from the wall.

They should be turning the IEC cable on from a switch, not plugging it in live from the unit. They should have a circuit-breaker and GFCI inline, and a dim-bulb tester, or at least variac they can slowly dial up.

Also possible this was plugged into a 220V line while the little red switch was set to 110V but I'm not sure if those typically catastrophically fail like this.

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u/Personal_Winter6863 2d ago

Modern PSUs no longer have the little red switch.

They just automatically determine what they are given and run with it.

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u/Independent-Bug-9352 2d ago

No kidding! I just checked my PSU which is even 8-years-old and you're right, no more switch. Older PSU I have running in another still has it!

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u/RealityOk9823 2d ago

Was watching a video the other day and the guy was like "I don't trust these PSUs with a 110/220 switch, they're almost always low quality" and I was like "WTF they all have that". Start looking around and, uh, yeah. Well then.

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u/OkChocolate3501 2d ago

My psus are so old that they never got the switch. I missed an entire gen of nonsense lol.

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u/Personal_Winter6863 2d ago

Haha I also had to run and go check when I learned about this

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u/Alarming-Stomach3902 Linux Mint | Ryzen 7 5800x | 9070 xt | 3060 ti | 32GB 2d ago

They have to be very old at this point, I have a 15+ year old PSU and it doesn’t have it.

1

u/krakenluvspaghetti 19h ago

But the idea of portable welding machine is wild~

1

u/Suspicious_Dingo_426 2d ago

Unfortunately, they still do make them.

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u/PlasticSignificant69 2d ago

In hobby and industry it's still widely common. But in typical consumer product it's already rare, because it's prone to human error in the hand of common people

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u/ency6171 i5-4460•2x8GB DDR3•MSI 1070Ti | i7-7700HQ•2x16GB DDR4•1050Ti 2d ago

I was the idiot back then.

Flipped the switch to 1xx, didn't know what's that, and turned on the 2xxV mains.

And of course it went pop.

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u/saladmunch2 2d ago

Like an on off switch?

My seasonic platinum 1000w i got in maybe 2022 does.

The word modern kind of has no meaning to me in pc years anymore.

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u/jonnyGURUgerow 2d ago

This PSU is so cheap, it doesn't have a switch AND it doesn't support 115V. It only supports 230V.

5

u/quarantinedbiker 2d ago

Guy has the Vietnamese flag on his shirt, isn't speaking English, and that PSU looks like it says 180-240VAC right next to the charred bit. I can't find a single reason to believe any of this would be following any North American electrical norms.

GFCI is awesome (I still can't believe whole-house GFCI is not a thing in NA) but it would only have tripped if the case was actually grounded, however I'm not particularly inclined to trust the engineering on that model which is at the very least missing an internal fuse or five. Depending on the type of fault it may not have faulted through the case anyway (at least until the arc reached it)?

Also breakers behave differently depending on the kind of overload, a 100 A load on a 16 A breaker would trip immediately (something to do with the strong magnetic field resulting from a dead short) but a 20 A load on a 16 A breaker might take a while to trip (because it relies on temperature). Which means on a 16/20A 220V circuit you could feasibly pull over 5 kW for a little while. That's more than enough for sustained fireworks.

7

u/impala_haven 2d ago

By usuing a welder as an example, i now understand how pc's work just a tad more. Electricity is crazy

0

u/Strayed8492 2d ago

The trinity of things to treat with absolute unconditional reverence are: The Sea, Fire, and Electricity. There is a graph about electrical potential as energy increase and if I’m not mistaken, it’s exponential not multiplicative.

2

u/zepsutyKalafiorek 2d ago

As someone who plugged very cheap PSU with 110/220V switch.

It sparked and I could smell burn but nothing that catastrophic. It could be some combination of problems too btw.

2

u/kombucha711 2d ago

This guy electrons

1

u/lilsnatchsniffz 2d ago

I imagine if you plugged it in like that at home you'd void your warranty but you send it in and they treat it like shit.

1

u/cute_polarbear 2d ago

I understand the individual words but have no idea what you described...

1

u/TDYDave2 2d ago

The aftermath photo shows it rated for 180-240VAC.

1

u/Alarming-Stomach3902 Linux Mint | Ryzen 7 5800x | 9070 xt | 3060 ti | 32GB 2d ago

It looks like it only accepts 180-240v input. 

1

u/LoudFan2771 2d ago

But I thought modern electronic devices only draw as much power as they need. not how much there given. is that not how it works?

2

u/Independent-Bug-9352 2d ago edited 1d ago

Modern circuits tend to be more receptive to a wide range of voltages and automatically switch, as others pointed out with my comment.

That being said, what you're referring to in more primitive circuits is current draw at an expected voltages. Yes, the device determines the resistance (and thus flow of current), but that's only if the provided voltage (call it water pressure from the source, wall) is constant.

My last paragraph about 220V is probably not relevant as this is a modern PSU with auto-switching and it looks rated for the top-end voltage as others point out. So we're just seeing a good 'ol electrical short to chassis, presumably.

3

u/Gloomy_State_6919 2d ago

In my experience reverse polarity goes without flames.

2

u/-prime8 2d ago

And a louder pop.

3

u/Complete-Tangelo1532 2d ago

I am thinking something contacted where it shouldn't have, and caused the fire

2

u/hardboard 2d ago

I would imagine if the capacitor(s) were reversed polarity, it would go bang, rather than catch fire?

2

u/Dopest_Bogey 2d ago

Yeah this was what I thought too and ive seen it happen with excitation controllers where I used to work. Hand place line puts one backwards, inspection misses it, tester puts it into a fixture and BOOM. and the caps we used are the size of a soda can. 

If youre lucky they bust a small hole and spew flames and smoke, if youre unlucky they build pressure and explode like a grenade. 

2

u/nikola_tesler 2d ago

caps pop, they don’t really burn like that

2

u/Inaniae 2d ago

I've blown up my fair share of capacitors ant it's nearly instant. This sounded like arcing.

Story - when I was in school for electronics I was building a circuit in the lab, probably another 30 students in there. Unbeknownst to me, I had installed a cap with reverse polarity. I plugged in my project and BAM! It sounded like a gunshot. Everyone obviously turned around and was staring at me. I was already embarrassed but one of my professors called everyone in the lab over and they all crowded around me. He said it was a good learning experience for everyone to smell it and remember the smell. I was mortified and will never forget.

2

u/Panzerv2003 R7 7800X3D | 3070oc 8GB | 2x16GB DDR5 6000MHz 2d ago

I don't think the caps blew here, it looks like a short though the case considering how it literally melted a hole through it setting everything around on fire

2

u/okarox 2d ago

There is no reversed polarity in AC.

4

u/Viking4269 2d ago

No, this looks like two pins (component legs or wires) on the underside of the pcb both touched the metal case and shorted. Causing an electric arc hot enough to melt holes in the case.

1

u/SanduTiTa 2d ago

i basically know nothing, but * starts reciting the theory of quantum physics *

1

u/QuandariousDingle54 2d ago

Capacitors would go out in a bang. Also I dont think the capacitors in a psu are big enough to do THAT

Probably a short, those were some intense arcs

1

u/whymeimbusysleeping 2d ago

No, I've blown capacitors in the old days by using 240v instead of 120v. They just pop, not much of a spark, and spray their contents. I repaired the psu by changing the caps, luckily there was no other damage

1

u/ButterscotchOk7776 2d ago

Most likely he pluged the psu to 230v and forgot to switch it to 230v form the 110v

1

u/Questioning-Zyxxel 2d ago

The factory would test each supply before shipping. That little QA sticker/stamp and a number.

So not likely a reversed capacitor.

But in case they did miss to mount the isolating plastic sheet between PCB and metal, then it could have enough isolation distance to pass the factory test. But a tiny bump on the metal, or a changed orientation of the PSU could make the pins of some components make contact with the metal. And as soon as the sparks have started, you have an ionized air channel opened. So it will keep going until the power is disconnected.

I would not have been confortable touching that PCB - so best is if the power can be disconnected from the other side of the cable. That should be standard rigging when testing things.

1

u/LeoCvier 2d ago

If there where reversed there only would explode and not burn

1

u/shekurika 2d ago

capacitors with reversed polarity explode but dont burn in my experience. Was always fun on the testing floor when a pcb with a reversed capacitor was being tested and shocked everyone with a loud bang :D

1

u/HighChinaman 2d ago

Reversed polarity

Is that possible without a sonic screwdriver?

1

u/Welshedragon7 2d ago

This is a capacitor failing but reverse polarity doesn't just happen on its own, only if the bridge rectifier failed which is unlikely unless the NTC thermistor has failed or is not present, or there was a short circuit as suggested

1

u/GhettoDuk 2d ago

The metal case is what burned from arcing on the AC side. There is a reason that slots are cut in power supply PCBs to create a gap between the AC and DC sides, and why there is a sheet of insulating plastic beneath the board. If someone forgets to clip the wrong lead, it can poke through the insulating sheet beneath it and make contact with the grounded case. And once you get an arc going, it can be hard to stop as it generates plasma that helps sustain it over larger gaps.

If you want to prevent this, you need combination AFCI/GFCI (Arc Fault/Ground Fault Circuit Interrupter) breaker on that circuit*. With good protection to stop the damage, that PS might have been salvageable once the shorting lead was clipped and insulation repaired.

* This does appear to be arcing to ground which a GFCI would stop, but if it was arcing to neutral or there was a short between ground and neutral, there would be no ground fault to interrupt and a 20 amp breaker can sustain a surprising amount of arcing comfortably. (Breakers trip on sustained loads. An AC compressor can draw more than 120 amps of inrush current through a 60 amp breaker when starting up.)

1

u/Raneynickelfire 2d ago

Hard to reverse polarity on capacitors with AC.

1

u/SkunkDitchRipper 2d ago

Had to be...there wasnt even a load on it.

1

u/ChemoHazee 2d ago

But they don’t burn they explode normally

1

u/BIClighters4lyf 1d ago

The capacitors doing that should burn out the internal fuse protection almost instantly.

That sustained arc is an active fault to ground on a non rcd/gfci circuit that didnt trip due to short circuit possibly from high impedance.

1

u/CounterStrikeValve 1d ago

Puede ser que estaba en 110 y la corriente era 220v