Author Topic: Be careful with those teardowns, kids!  (Read 20413 times)

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Offline TerminalJack505

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Be careful with those teardowns, kids!
« on: October 10, 2012, 02:07:26 am »
Teen electrocuted while working on unplugged computer

Quote
A 16-year-old is stripping down a family computer, which is unplugged. He dies. An autopsy reveals electrocution burns.

Apparently this happened when he took the PC's power supply apart.  I'm guessing there was still a lethal charge on the mains cap(s).
 

Offline Monkeh

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Re: Be careful with those teardowns, kids!
« Reply #1 on: October 10, 2012, 02:12:36 am »
Darwin at work.

More wildly inaccurate bullshit from the supposed experts and the media, too.
 

Offline FenderBender

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Re: Be careful with those teardowns, kids!
« Reply #2 on: October 10, 2012, 02:38:14 am »
Darwin at work.

More wildly inaccurate bullshit from the supposed experts and the media, too.

What did you expect?
 

Offline bullet308

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Re: Be careful with those teardowns, kids!
« Reply #3 on: October 10, 2012, 04:18:54 am »
:-/

Guess I need to post a sign over my bench... "When Working on Mains Stuff, Sit On Your Left Hand!"

I am gathering that it is unlikely to get a fatal zap from a big cap with one hand involved.
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Offline Monkeh

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Re: Be careful with those teardowns, kids!
« Reply #4 on: October 10, 2012, 04:27:01 am »
Darwin at work.

More wildly inaccurate bullshit from the supposed experts and the media, too.

What did you expect?

Nothing less.
 

Offline MrPlacid

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Re: Be careful with those teardowns, kids!
« Reply #5 on: October 10, 2012, 05:29:23 am »
Dave need to do a tear down of a computer powersupply immediately.  Dave, give your opinion and advice on how to properly tear down power supplies.
 

Online IanB

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Re: Be careful with those teardowns, kids!
« Reply #6 on: October 10, 2012, 05:48:37 am »
Dave need to do a tear down of a computer powersupply immediately.  Dave, give your opinion and advice on how to properly tear down power supplies.

Well see, there are these big round things that might have something written on the side of them like "300 uF 500 V". They might bite you if you touch their pins. It's a good idea to make sure you discharge them with a screwdriver or something before you go near them. (And watch out for the bang if you do that. It might startle you if it takes you by surprise.)
« Last Edit: October 10, 2012, 05:50:23 am by IanB »
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Offline Bored@Work

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Re: Be careful with those teardowns, kids!
« Reply #7 on: October 10, 2012, 06:05:02 am »
More wildly inaccurate bullshit from the supposed experts and the media, too.

Actually not. For a tech report in the media they were more accurate than usual. The website got it right
Quote
Still, though many teens now fancy themselves as technological experts

Yep, "fancy themselves" is exactly the point. "fancy themselves" because they can download a ringtone to their cellphone, install some memory in a computer, manage to spell Arduino, or manage turn on the microwave. While in reality they have no clue.

But the worst, they are ineducable. Just look here. Almost every week some idiot shows up, with an idea for an non-islolated power supply, with an idea to convert a computer SMPS into a spaceship, idiots promoting unsafe meters, idiots being proud that they got zapped at least 30 times. You name it, we got it here.

And dare you you tell them that something is not safe and they should keep their hands off. Ha! No, they are entitled to it, because the "fancy themselves as technology experts".

The video http://www.kctv5.com/story/19767067/teen-electrocuted-while ? Yes, inaccuracies like "power storage box" and an expert who is just a box shifter. But the basics are still right, electricity is dangerous, and nature doesn't care if you feel entitled.
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Offline Dago

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Re: Be careful with those teardowns, kids!
« Reply #8 on: October 10, 2012, 06:21:48 am »
Having played a lot with electrolytic caps I'm fairly sure touching the mains filtering caps on a computer PSU would NOT result in "electrocution burns". Causing tissue damage requires a LOT of energy (cause humans are mainly water). I'd be willing to bet it was plugged on...
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Offline westfw

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Re: Be careful with those teardowns, kids!
« Reply #9 on: October 10, 2012, 06:52:36 am »
I'm under the impression that a typical computer power supply will rather quickly discharge its main capacitors when unplugged, and it takes something special (like a picture tube or strobe circuit) to retain a lethal charge for more than a few moments.  True, or not?

That's not to say that you can't get unlucky with relatively low voltages.

I don't know what "electrocution burns" as seen in an autopsy might be.  Most (US) mains-caused electrocutions are going to be less than visible burn-causing events, but they could leave behind something that medical professionals might call "burns."

And it's not to say that I've never done anything stupid.  I especially remember the AC cord I sliced through with a knife, that turned out NOT to be the cord I had just carefully unplugged.  (It ruined a good kitchen knife!)
 

Offline ThievingSix

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Re: Be careful with those teardowns, kids!
« Reply #10 on: October 10, 2012, 07:02:31 am »
Quote
Yep, "fancy themselves" is exactly the point. "fancy themselves" because they can download a ringtone to their cellphone, install some memory in a computer, manage to spell Arduino, or manage turn on the microwave. While in reality they have no clue.

But the worst, they are ineducable. Just look here. Almost every week some idiot shows up, with an idea for an non-islolated power supply, with an idea to convert a computer SMPS into a spaceship, idiots promoting unsafe meters, idiots being proud that they got zapped at least 30 times. You name it, we got it here.

And dare you you tell them that something is not safe and they should keep their hands off. Ha! No, they are entitled to it, because the "fancy themselves as technology experts".

The video http://www.kctv5.com/story/19767067/teen-electrocuted-while ? Yes, inaccuracies like "power storage box" and an expert who is just a box shifter. But the basics are still right, electricity is dangerous, and nature doesn't care if you feel entitled.

Sounds like you fancy yourself to be an expert at safety?, i bet you didn't pick up all that knowledge from a textbook. But of course, dare i not tell you such a thing.

Quote
But the worst, they are ineducable. Just look here. Almost every week some idiot shows up, with an idea for an non-islolated power supply, with an idea to convert a computer SMPS into a spaceship, idiots promoting unsafe meters, idiots being proud that they got zapped at least 30 times. You name it, we got it here.

Maybe "some idiot" is posting that design so he can get feedback and learn about what's wrong with it and how to improve it. Why in the world would he post a perfectly engineered design that meets all safety standards? Oh that's right, I forgot the standards book costs over $400, and we're not all professionally trained engineers supported by the company credit card. If "idiots" such as Michael Faraday, Nikola Tesla, Thomas Edison and  J.J. Thomson, to name a few, hadn't been "playing" around with potentially dangerous stuff we wouldn't even know as much as we do about electromagnetism today. If anything we learn more from our mistakes than our failures, and ultimately every safety precaution should be taken, but at the end of the day, if you don't take risks you don't learn anything.

To add, i thought i'd do a little investigative work, and i found that there were no records of death by police on the day mentioned "August 16th" and the news article cites KCTV as the source, since when did a news station become a reliable source??

Quote
"Shawnee police said too many don't realize that computers carry a charge in them even when they are unplugged and broken. They urge everyone not to strip an old computer to build a new one. "There's a real danger if you don't know what you are doing," said Shawnee Capt. Dan Tennis.

So essentially the police said what was actually quoted, and the reporter made up the rest. To add to that it sounds like they've simply dug up an old story to fill "news time" with a little fear mongering.  They mentioned nothing on the boy himself, his family, any other circumstances surrounding his death, or even the death report. Hmnn i smell a fishy news story.

http://gsh.cityofshawnee.org/WEB/PoliceCMS.nsf/vwContent/PoliceDailyActivity?OpenDocument&Start=1&Count=610&Expand=2
« Last Edit: October 10, 2012, 07:20:10 am by ThievingSix »
 

Offline MrPlacid

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Re: Be careful with those teardowns, kids!
« Reply #11 on: October 10, 2012, 07:06:39 am »
IanB, I was thinking Dave should follow the news so he can stand out more. That is what those guys who appeared on the news over and over again do. I think people would start scouring youtube for how to open computer power supplies videos, so it would be a good time to make such a video. And Fast.

BTW,  is a 300uF 500V the actually value of capacitors in a computer power supply?  I would thought it would be much larger.
 

Offline MrPlacid

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Re: Be careful with those teardowns, kids!
« Reply #12 on: October 10, 2012, 07:10:57 am »
Having played a lot with electrolytic caps I'm fairly sure touching the mains filtering caps on a computer PSU would NOT result in "electrocution burns". Causing tissue damage requires a LOT of energy (cause humans are mainly water). I'd be willing to bet it was plugged on...

I am with you. My thought is that the boy had it plugged in and electrocuted himself. Guardian disconnected it and rather claim that it was unplugged. If they don't they'll probably be charged with child endangerment or something.
 

Offline retiredcaps

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Re: Be careful with those teardowns, kids!
« Reply #13 on: October 10, 2012, 07:12:33 am »
I'm under the impression that a typical computer power supply will rather quickly discharge its main capacitors when unplugged, and it takes something special (like a picture tube or strobe circuit) to retain a lethal charge for more than a few moments.  True, or not?
A few months ago I worked on a LG 2234 monitor.  It was made in 2008 so it is fairly "modern" SMPS lcd power supply.

The big cap retained its 165V DC charge overnight after I unplugged the lcd from the power bar before going to sleep.  I had to discharge it manually.  Now maybe this is a one off, but I always check the large filter capacitor with a multimeter before working on anything now.

A couple of ATX power supplies that I have worked on takes several minutes to discharge.  Most, but not all, SMPS power supplies that I have worked on in lcd monitors discharge the big cap in usually less than 1 minute.
 

Offline sorin

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Re: Be careful with those teardowns, kids!
« Reply #14 on: October 10, 2012, 07:14:20 am »
Quote
an autopsy revealed electrical burns
I dont thing that 300V 500uF capacitor can do this...
 

Offline grumpydoc

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Re: Be careful with those teardowns, kids!
« Reply #15 on: October 10, 2012, 07:33:46 am »
Quote
I dont thing that 300V 500uF capacitor can do this...

Energy = 0.5 CV2 so 22.5J. Water (we're mostly water) has a heat capacity of 4.2J per g per  °C so, no, that much energy would be incapable of producing much in the way of significant deep burns - maybe some superficial ones.

That said electrical burns often look much less serious on the surface because all you see is the relatively small entry and exit points for the current - the current path spreads out in the body and considerable heating and damage to tissue can take place.

The stored energy is enough to interfere with the heart rhythm though if he was unlucky enough to manage to get the current path to flow across the heart - that's really the theory/folklore behind the "sit on your left hand" rule.

As has been observed these caps can hold high voltages for some time, especially if the power supply is faulty and there is no load to drain the charge. In this case it seems likely that the PSU was faulty as it was being "stripped for parts".
 

Offline vk6zgo

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Re: Be careful with those teardowns, kids!
« Reply #16 on: October 10, 2012, 07:35:00 am »
I'm under the impression that a typical computer power supply will rather quickly discharge its main capacitors when unplugged, and it takes something special (like a picture tube or strobe circuit) to retain a lethal charge for more than a few moments.  True, or not?

That's not to say that you can't get unlucky with relatively low voltages.

I don't know what "electrocution burns" as seen in an autopsy might be.  Most (US) mains-caused electrocutions are going to be less than visible burn-causing events, but they could leave behind something that medical professionals might call "burns."

And it's not to say that I've never done anything stupid.  I especially remember the AC cord I sliced through with a knife, that turned out NOT to be the cord I had just carefully unplugged.  (It ruined a good kitchen knife!)

Actually picture tubes are highly overrated when it comes to danger from them remaining charged.
The EHT voltage is quite high,& they do retain charge for quite a while,but their capacitance is too low to supply a lethal shock.

It would be quite easy to see how much charge is available in the caps after the mains rectifier in a switchmode power supply.
I would have thought,nasty,maybe life-threatening,but electrical burns seems a 'bridge too far".
 

Offline tom66

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Re: Be careful with those teardowns, kids!
« Reply #17 on: October 10, 2012, 07:43:44 am »
Typical capacitor in a genuine 300W power supply without PFC: about 1200uF 200V, times two. Caps are in series to make a 600uF 400V cap, the centre tap is used as part of the half-bridge converter (I think.)

Typical capacitor with PFC: around 220uF (low 250W Dell supply) to 1000uF (1200W beast - IBM ThinkCentre RAID server PSU), at 420-450V.

The caps would typically discharge within about 2 minutes due to the constant ~0.5W lost in the standby circuit and other parts of the PSU such as bleeder resistors.

Both would cause a bad shock if touched: if you had a weak heart, maybe even fatal... but it wouldn't cause burns.

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Offline David_AVD

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Re: Be careful with those teardowns, kids!
« Reply #18 on: October 10, 2012, 08:16:03 am »
A faulty switch-mode power supply (that didn't start) can certainly hold a charge for some time on the main filter capacitor.  Some units have a bleed resistor, but not all.
 

Offline amyk

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Re: Be careful with those teardowns, kids!
« Reply #19 on: October 10, 2012, 08:31:29 am »
My bet is on it being plugged in, or he was particularly lucky to have bridged the cap across his heart with both hands. Probably the former, as the amount of stored energy isn't what would cause the burns described.

Quote from: vk6zgo
Actually picture tubes are highly overrated when it comes to danger from them remaining charged.
The EHT voltage is quite high,& they do retain charge for quite a while,but their capacitance is too low to supply a lethal shock.
The danger of those is not from the shock itself, but from the surprise making you do something else, like drop the set or smash your hand against the neck. I've gotten static shocks on dry days, those can be tens of kV and the secondary effects are what really makes you do something stupid, not the shock itself.
« Last Edit: October 10, 2012, 08:33:30 am by amyk »
 

Offline Bored@Work

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Re: Be careful with those teardowns, kids!
« Reply #20 on: October 10, 2012, 08:33:37 am »
@BoredAtWork: You seem bitter at people?

No, I am not bitter at people. I am annoyed by these fruitcakes who think they are an engineer just because then can rip off the latest Lady Gaga abomination and load it as a cell phone ring tone, or who glue Arduino to everything. And I am annoyed by those companies like Make who encourage them and rip them off.

Just read this thread. It didn't take long and you have a bunch of fruitcakes coming out of the closest telling you that the primary cap in a SMPS can't kill you. Because, wait for it, they survived it. Hint, those who didn't survive it can't talk any more. Hint 2, if you get zapped you failed, nothing to be proud of. They should sit in a corner, being ashamed of themselves, think about how to avoid it in the future, instead of proudly announcing that this is all harmless. And it does not matter if the boy in the current case was killed by it or something else. That doesn't change the fact that it is dangerous.
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Offline G7PSK

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Re: Be careful with those teardowns, kids!
« Reply #21 on: October 10, 2012, 09:04:35 am »
At one time many large high voltage caps had a built in discharge resistor,on others there was one across the terminals, what has happened to these.
 

Offline LoyalServant

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Re: Be careful with those teardowns, kids!
« Reply #22 on: October 10, 2012, 09:04:40 am »
I have to agree with @boredatwork...
I have tried to show a few young fellas a thing or two and basic safety like keeping one hand behind your back.
They won't do it.. they are invincible.

I guess in a way they win a Darwin award?

Some of these articles from supposed experts are painful to read too....
 

Offline T4P

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Re: Be careful with those teardowns, kids!
« Reply #23 on: October 10, 2012, 09:45:10 am »
the last ATX PSU i take apart has  massive HV warnings everywhere ...  ::)
And even a "no user serviceable parts inside" on the outside ... Yeah sure ...
Give them 15mins max, it won't keep much voltage much longer, unless it's so broken ... Well, always use a capacitor discharging pen to be sure (I used to have giant HV stickers then i dumped them  ;) )
As it's a a PSU for a PC it's not going to keep much of the voltage unlike what you see with a monitor ... they can run on the standby for like 5mins after flipping the switch (I'm talking about a Samsung 4 series 165Watt 22" TV not Monitor!)
 

Offline HackedFridgeMagnet

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Re: Be careful with those teardowns, kids!
« Reply #24 on: October 10, 2012, 12:05:38 pm »
I'm skeptical too of the facts presented in this article.
As others have pointed out you're not going to die of burns from these caps.
Maybe you can die from heart failure from these caps but you probably would have more chance of being struck by lightning.

Actually I think the whole electrical safety thing is a bit overrated, as far as I know the most dangerous things are cars, rich food and alcohol, but I'm not about to do the risk analysis.

Remember:
Don't turn it on, take it apart.





 


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