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Electronics danger

Discussion in 'Science & Technology' started by Aleksander, Nov 16, 2012.

  1. Aleksander

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    I was reading a book about electronics and was thinking about the danger you might have while working on old parts by disassembling them, since the book is clearly stating not to do that until you know what you are doing.

    Is there really any danger on old electronic parts which are plugged off normally and I am asking because nothing like this happened before to me
     
  2. [Ion]

    [Ion] WCG Team Assistant

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    Some. Motherboards and graphics cards are (or at least were) frequently made with lead solder. Lead, as you probably know, is toxic. So it's always best to wash your hands thoroughly when you're done. Power supplies hold a great deal of power, even after sitting unplugged--they're regarded as the most dangerous components. Don't do anything with them unless you know what you're doing. But just use common sense and wash your hands and you'll be OK.
     
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  3. sneekypeet

    sneekypeet Unpaid Babysitter Staff Member

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    PSU components can hold a charge and zap the piss out of you...same for TVs and such with Capacitors that don't discharge unless properly grounded to earth.
     
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  4. Aleksander

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    Yeah, now i remember watching psu reviews when they hold that bracelet for grounding!
     
  5. erocker

    erocker Super Moderator Staff Member

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    That bracelet is for static electricity. A capacitor on a PSU can hold enough charge to kill you. I remember reading something in the past year where some kid died from messing with his PSU.
     
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  6. Jack1n

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    Really? i got zapped by a PSU that i forgot plugged in the power outlet while i was swapping a fan,it hurt abit but it was nothing really.
     
  7. 95Viper

    95Viper

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    No No No... that bracelet, as you call it, is a static discharge device to protect sensitive components from STATIC discharge. IT IS NOT TO PROTECT YOU FROM ELECTRICAL SHOCK!

    Always use the one hand rule when testing electricity and don't ground yourself anywhere.
     
  8. [Ion]

    [Ion] WCG Team Assistant

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    It all depends on the capacitor. The big ones hold a ton of charge--you cearly were ucky and only got "hit" by one of the weaker ones. Regardless, I can't imagine that you were disassembling a PSU while it was still plugged in :wtf:

    If you are going to....unplug it, and then try to power up the system. That will clear most of the charge--then, ideally, leave it sitting for a few weeks. Then it will be pretty safe to disassemble.
     
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  9. Aleksander

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    LoL, I am new to electronics so wait until I read some new stuff on the book and understand that bracelet thing :)
    Ty for replies!
     
  10. Easy Rhino

    Easy Rhino Linux Advocate

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    i hear that if you disassemble older electronics wearing nothing but underwear a hot chick appears out of nowhere and gives you a helping hand.
     
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  11. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Oh for crying out loud.
    The capacitors in a PSU will discharge in milliseconds through bleed resistors or just the general resistance in the circuits components once the power is removed.
    At worse case a few seconds. If you are paranoid leave it for 15 minutes and all capacitor voltage levels will certainly have dropped to safe (not able to overcome body resistance) levels.
     
  12. Aleksander

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    Actually, that happened with a cigar :toast:
    From what i am reading, electricity will always be there in the conductors, even if you turn off everything.
    It will not have enough current to power up again!
     
  13. [Ion]

    [Ion] WCG Team Assistant

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    Fair enough. I'm just repeating what my Dad told me. Thanks for the correction. :)
     
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  14. Aleksander

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    Depends if you are talking about Electric with Amperes and Electronic
    with miliAmperes which means far less electrons go through a point than electric.
    But if you are talking about the psu i guess that part is electric!!!
     
  15. acerace

    acerace

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    My dad is always diassembling old electronic parts, mostly TV's and radios ( lately hi fi components) and if can, repair it. Nothing happen to him. Well, he got almost 30 years experience in electronics, and I think that's why.
     
  16. Aleksander

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    I have a new question about electronics:
    Why modern electronic circuits are described with conventional current and not from negative to positive? This sounds absurd
     
  17. Aquinus

    Aquinus Resident Wat-man

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    He might have been talking about CRT TVs. I know that those hold a charge for a little while and give you a bit more of a zap than a PSU does.
     
  18. silkstone

    silkstone

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    DC current is pretty safe, .3A of DC current can cause fibrillation, which is about 5x more than needed for AC. Considering that the bodies resistance is at least 1,000 ohm (when soaking wet) and over 1M ohms when dry, you would need a potential difference of 333 V at a minimum. another important factor is duration and path the current takes. The duration of discharge for a capacitor is extremely quick and the fact that the current would have to travel across your chest mean that in theory, they could kill you, it is very very unlikely.

    further reading: http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

    I've actually been shocked by layden Jars where the current travelled across my chest, it scared the hell out of me, made me short of breath for a while and hurt pretty bad. I didnt realize how dangerous they were at the time as they we only connected to a van de graff type machine (can't think what it's called now). So even if the charge from a capacitor isn't deadly, it can hurt like hell and i would strongly recommend being extremely careful around them.
     
    Last edited: Nov 17, 2012
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  19. eidairaman1

    eidairaman1

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    they are talking about Capacitors, CRT Monitors and TVs can hold a charge for a very long time.

    Of course the obvious is when the components are plugged into a wall/PSU or on batteries too.

    http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html
     
    Last edited: Nov 17, 2012
  20. silkstone

    silkstone

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    The values in the tables from that link are for AC current btw, also the period for the discharge from a capacitor is in the range of nano or microseconds.

    Again, you really don't want to get shocked by one as they can hurt like hell, they really don't carry enough charge to be truly dangerous unless you are talking about one the size of your fist. You are more likely to die driving to work than being shocked by a psu cap, but you should still be careful as it is still a possibility.

    Tazer's work using capacitors bigger ones than found in PSU's (Edit - Some of the cheaper ones use smaller caps though). They also use AC current and the prongs penetrate the skin (vastly reducing the resistance of the human body). Those things can be deadly, but in general they are considered safe for use by the police.

    You'd prolly be best just to discharge all the caps beofre working on them, get a thin metal screwdriver and rest it across the legs of each of the bigger caps, that should make a psu much safer to work on.
     
    Last edited: Nov 17, 2012
  21. Aleksander

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    The bracelet i was talking about before, is an anti-static wristband.
    I learned that it is used for earth ground, but it is basically even more dangerous than not having it.
    If an earthquake happens or another similar thing, that becomes energized.
    You end up shocked!!!
     
  22. Sasqui

    Sasqui

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  23. CJCerny

    CJCerny

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    Some electronics, like older TV's and CRT's, do indeed have capacitors in them that are large enough to kill you if they are fully charged when you discharge them. It is not uncommon to find a 20k volt capacitor in a TV made in the 50's or 60's. They don't hold a lethal charge more than about an hour or so after the TV is unplugged, however. Best advice is to not work on any device that you don't understand the dangers of. For the most part, unplugged eletronics are safe to work on.
     
  24. Kreij

    Kreij Senior Monkey Moderator Staff Member

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    Yes, be very careful working on CRTs and if you are going in hot with an oscilloscope make sure you use an isolation transformer.

    We had a teacher who always harped on us about using isolation transformers.
    We got in 3 new CRT TVs to work on at school and the first thing he did was forgot to use the transformer and blew the bridge rectifier right out of the TV.
    He was on the receiving end of a lot of ribbing for that one. lol
     
  25. Completely Bonkers New Member

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    CAREFUL when working on live equipment. Especially using things like probes and voltmeters where inadvertent holding of the unsheathed part of the probe means YOU can be the short circuit from one side to the other... across your heart.

    ALWAYS when working on live equipment use at least one probe with a croc clip, and set it safe. Only HOLD one probe, never two, ie never one in each hand.
     

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