Teen electrocuted while salvaging parts from a computer

By Shawn Knight ยท 98 replies
Oct 12, 2012
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  1. Anyone that's worked with computer hardware knows there are some risks involved. Sharp edges inside a case can leave your hands and fingers looking like you lost a thumb-wrestling match with Edward Scissorhands not to mention the potential to short...

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  2. ikesmasher

    ikesmasher TS Evangelist Posts: 3,002   +1,322

    RIP dude...
    But it should be well known that you DONT mess with power supplies unless you're like a trained professional.
  3. nazartp

    nazartp TS Enthusiast Posts: 178   +12

    "Electrical burns"? Seriously? He must have been grounded with the wrist band and touched the capacitor with another for electricity to flow through the heart to kill him. It must be really bad luck to get killed by a capacitor charge.

    In any case, very sad to read this. My condolences to kid's family.
  4. Alexmx

    Alexmx TS Member Posts: 23

    I'm no rocket surgeon but, does a power supply really stores all that energy after unplugged?

    What I always do after unplugging is press the power button on the computer to drain the remaining electricity
    valentyn0 likes this.
  5. EEatGDL

    EEatGDL TS Evangelist Posts: 568   +241

    Very sad indeed, as the article said: dismantling a PSU is not worth it. Very strange how the conditions could have been in order to make that possible with just a loaded capacitor.
  6. andrewdoyle88

    andrewdoyle88 TS Booster Posts: 114   +96

    Bad luck Brian takes apart his first computer... Dies. I shouldn't be joking though poor kid just really bad luck
  7. noel24

    noel24 TS Evangelist Posts: 359   +203

    Yeah, read numbers on those big one, they can store pretty punch. Its a good idea to push a power button on an unplugged PC and leave it overnight for those charges to dissipate, before raplacing fan or capacitor.
  8. nazartp

    nazartp TS Enthusiast Posts: 178   +12

    Sadly it does. Pressing the button does discharge the capacitors though. I am just REALLY surprised that the kid got killed. In 30+ years tinkering (and I'm an engineer by background) I got zapped more than once. Most typical case you brush something with your hand while touching the chassis with the same hand. Painful, but hardly damaging. To get killed you need to really have a path for electricity to flow through your vital organs, primarily brain and/or heart. That's why I think he had an anti-static bracelet properly grounded.
  9. nazartp

    nazartp TS Enthusiast Posts: 178   +12

    Out of sheer curiosity computed the energy stored in a typical capacitor. At 120V and capacitance of 2000 uF (pretty typical for a power supply) the energy stored is about 14.5 joules. Standard automatic biphasic defibrillators deliver first shock at around 150-175 J. So 14.5 is pretty low.
    ghasmanjr and wiyosaya like this.
  10. nismo91

    nismo91 TS Evangelist Posts: 930   +33

    this. then you'll see the system & cpu fan turns on for a brief second.
  11. PC EliTiST

    PC EliTiST TS Enthusiast Posts: 51   +7

    What the? Indeed, I have only opened PSU just once in my life... It was when I built a new PC, I opened the old one to clean the fan and generally the inside... You know, because it is inaccessible, it gathers a lot of dirt after a few years.

    My M/B AND my PSU both have LED-lights to warn me when there's still electricity. After I unplug, it usually takes ~3 secs until the LED-lights go out. I hope this indication is enough... Unless the electricity in capacitors is different and the LED cannot measure it...
  12. wiyosaya

    wiyosaya TS Evangelist Posts: 1,946   +765

    I smell a lawsuit coming here. No discharge resistor across the capacitor.

    However, I highly doubt that the kid unplugged the computer. Voltages and energies are so low in a PSU _AFTER_ you have unplugged it that to me, it sounds like the kid still had it plugged in; otherwise, I don't see the seriousness of the resulting burns.

    IF the kid had a CRT and the kid touched the anode lead of the CRT after unplugging it, I could see this happening because the voltage is extremely high.

    For anyone interested, the formula for energy storage in a cap is


    where C is in farads and V is in volts.

    Even in typical caps on the mains line of modern switching supplies, the energy is about 60 J for a 240 V main, and will discharge quite quickly once the PSU is unplugged as it continues to power the switching circuits until it discharges.

    As I said, I am willing to bet the kid had failed to unplug the PSU from the mains, and touched the wrong spot.
  13. wiyosaya

    wiyosaya TS Evangelist Posts: 1,946   +765

  14. cliffordcooley

    cliffordcooley TS Guardian Fighter Posts: 9,745   +3,710

    You are reading words from someone who has been shocked more times than he can could from wall current while touched a direct ground. I've been bitten by automotive coils which charge up thousands of volts just to be able to create a spark for ignition. Talk about an experience try unplugging a coil while the engine is running(did this once because the key was broke and couldn't kill the engine).

    This reminds me of the stories you read or hear about people sky diving and parachute failing then living to tell about it. Reminds me of the people in accidents where the vehicle is shredded and live to tell about it. Then you read a story about someone who hits a ditch at 20/25 miles an hour and dies with little damage to the car.
    Lets not forget the people struck by lightning that live to tell about it. And then reading this story about a young kid who appears to do everything by the book, dies from a fraction of the current behind a lightening bolt.

    Reading such contrasting stories will always leave confusion in heart and mind of those reading and especially the ones living them. Stories such as this one will never be understood, my condolences to this family for their loss.
  15. Gareis

    Gareis TS Member Posts: 73   +14

    I've never thought to do that before, thanks for letting me know ;)
    ( of course, I've only Been working with computers for a few years...)
  16. Per Hansson

    Per Hansson TS Server Guru Posts: 1,960   +218

    This is good advice but it only applies when the powersupply is working, and chances are high that if you need to disassemble it it's actually not working properly...

    First of all the primary capacitor or capacitors in a computer's switch mode powersupply (PSU) sit after the input rectifier, which converts the incoming AC voltage to DC voltage. In the case of 120VAC input power there is also a voltage doubler stage active which does what the name implies.
    Secondly if the PSU is a modern design it will instead have a APFC stage (Active Power Factor Correction) which sets the voltage at the primary capacitors to ca 400v

    Have you actually ever opened a cheap Chinese built PSU? (A $20 PSU as the linked news movie talks about)
    Most ones lack any and all input filtering, there are no X or Y capacitors, no MOV's and no coils to be seen, just jumper wires on the PCB where the missing components should be.
    What makes you think they would hesitate to not install the primaries bleeder resistor?
    I have a charger for a camera right here lacking exactly that, made in China of course.
    Actually the majority of PSU's power switches do not switch of both Line & Neutral, which is required by law in Europe.
    Because many European countries use the Schuko plug which is not polarized, meaning it can be inserted either way (AC power does not care, so we can flip the live and neutral in any equipment).
    This has the interesting side effect that when the PSU switch is off there might actually be power present through the entire PSU all the way back to the switch!
    All you have to do is provide a path for the Neutral and there will be a circuit formed.
    Like if you hold the PSU's chassis while touching the primary sides heatsinks!
  17. TomSEA

    TomSEA TechSpot Chancellor Posts: 2,720   +860

    I'm not a PS guru, so had no clue you could even get shocked, much less die from one.

    Not that I'd ever tear one apart, I'd have no reason to. But good thing to know and sorry to hear about the kid.
  18. ..err, is this possible? I once get electrocuted accidentally bumped with loaded capacitor from one of my lab device that has diameter twice of my finger and all I got is only minor burns on my breast :p
  19. nazartp

    nazartp TS Enthusiast Posts: 178   +12

    Yep, forgot about that. It's still a very strange death. Electric burns and death just from a cap. Baffles me unless he forgot to unplug the computer. Gotta go show the article to my son - should put some fear of electricity into him.
    valentyn0 likes this.
  20. cliffordcooley

    cliffordcooley TS Guardian Fighter Posts: 9,745   +3,710

    I'm sure it takes longer than 3 sec to take a PSU out of the case and remove the screws from the PSU cover.
    If there is any voltage on the circuit, the LED's will be illuminated. There is probably internal switches that cut-off the each rail of power from the PC, leaving main power fully energized. How else could you explain the short burst of electricity while pressing the power button mentioned above. I personally have not observed the short burst but understand how its possible.
    Source link

    For a PC to maintain standby power, the main power source can not be turned off. Only power rails can be switched off, leaving the PSU fully charged and waiting for a power good signal from the motherboard. This is a system which was needed for allowing the operating system, control of powering down the PC. Once the motherboard gets a signal from the operating system that it is safe to shutdown, the power good signal is removed which tells the PSU to switch off all rails. The motherboard must maintain power though so it can re-initialize the power good signal and turn the PC back on.
  21. cliffordcooley

    cliffordcooley TS Guardian Fighter Posts: 9,745   +3,710

    Respect would be a better word. Fear can lead to other problems.
  22. I've been shocked many times working on various electronics over the years, some are minor and some hurt quite bad. I've had some friends that have had some bad zaps as well. One ended up in the hospital and they said if he had used his other hand to complete the circuit he may not have survived.
  23. Well its not the jauls that count it is that thing the band was formed around called AC/DC is the big killer. Remember computers like direct current not alternating which is more user friendly. This is why you have that in your house. For dc even in smaller amounts can kill you. It stops your hart. AC alternates at 60 herts to match your pulse a little closer. And DC just fibrillates you. This is why the warning. Same thing in a Television old type though that one is much higher. This is why they tell you never ground yourself when inside a power supply. That is the last thing you want to do and yes you could have been zapped many times but it only takes one time grounded to stop your heart. Also this may have not been fatal if he had worked with a partner for the current probably only stop his heart with no fatal damage. He just needed CPR within I don't know about 5 min. That is about the time you are allotted to avoid serious brain damage. Loner is what killed him or his dad getting home late. I guess this is what the scene is like when you try to prove a warning wrong but all you are able to manage is prove it dead right.
  24. lipe123

    lipe123 TS Evangelist Posts: 719   +236

    He must have had a weak hart to start with or some other underlying issue. In the states those caps only charge upt o 200V and its converted to DC.
    The discharge from that is enough to give you a good prick but its almost always between two fingers on the same hand! You'd have to try really hard in the first place to get one hand per terminal/track its soldered to.

    If he had burn marks on his body there was MUCH more to this story than just stripping a PSU (which you shouldn't do anyways!).
  25. danhodge

    danhodge TS Member Posts: 80   +13

    I have messed around with my old PSU trying to retrieve a fan, I didn't realize there was so much danger :S
    Not doing that again!

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