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A daycare in my city has taken a donation of desktop and laptop computers for the older children to take apart.

I am concerned that the various capacitors would present a shock hazard for the children, and have volunteered to discharge them.

The original plan was to unplug the computer, hold the power button to discharge the PSU output capacitors, then cut off an ATX cable and short the rails to ground, which should take care of the electrolytic filter capacitors on the motherboard.

Would this create a floating potential that could cause a shock if someone were to be touching the case and something else that was properly grounded?

Also, would there be a good way to discharge the PSU input capacitors?

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    \$\begingroup\$ You're wasting your time. The voltages present anywhere on a PC motherboard (under normal circumstances) are nowhere near enough to present any kind of shock hazard - even while powered up and running. \$\endgroup\$
    – brhans
    Mar 15, 2017 at 14:31
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    \$\begingroup\$ The PSU is the only component with potentially hazardous voltages. Remove the PSU, and you're done. (Assuming you're not dealing with old CRT monitors as well.) \$\endgroup\$
    – Dampmaskin
    Mar 15, 2017 at 14:31
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    \$\begingroup\$ As for the PSU input caps, just let the PC sit on a desk for a few hours to be sure the caps discharge through the bleeder resistors. \$\endgroup\$
    – bobflux
    Mar 15, 2017 at 14:33
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    \$\begingroup\$ Other hazards exceed voltage ( after taking @Dampmaskin advise), including RoHS non-compliance, leaky batteries, small-part choking hazard to name a few. \$\endgroup\$
    – glen_geek
    Mar 15, 2017 at 15:14
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    \$\begingroup\$ Laptop batteries are a bigger hazard than most people think. \$\endgroup\$
    – pjc50
    Mar 15, 2017 at 15:49

2 Answers 2

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The highest voltage you are likely to see on the motherboard of a desktop PC is 12V. Even if the capacitors aren't discharged, that's not going to kill anybody. On a laptop, it could be up to 19V, which is still pretty harmless.

The PSU of a computer may have a few hundred volts when in use, but that should dissipate fairly quickly. Leave the computers off for a few days, and it will be gone.

Beware of letting smaller children near all the bits left over after disassembling a computer. The little backup batteries on the motherboard can be pretty nasty if swallowed, and the other components can contain all sorts of toxic chemicals.

Beware of shorting out laptop batteries, as lithium cells are notorious for catching fire

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The voltage on motherboard is very low and will not present danger. UNLESS it has build in PSU on motherboard which is very rare these day, they used to do that on 1980s/1990s old computer but not anymore due to CE certification and safety reason.

If you so concern, you can short whole motherboard with antistatic mat or foam.

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