With capacitors being used in different parts of the automobile, such as in conjunction with audio equipment, what is the correct way to discharge them in order to prevent personal injury?


I know two ways, depending what the equipment is:

1) to allow sufficient time for self-discharge, usually stated by the manufacturer when dealing with the high energy ignition circuits,

2) for the large audio power capacitors then to discharge them through a power resistor of about 4k ohms...

  • How does one go about #2? #1 seems pretty obvious ... you just wait the specified time. – Pᴀᴜʟsᴛᴇʀ2 Oct 22 '18 at 13:41
  • Professionally designed equipment should have the resistors to automatically discharge the caps already built in. Leaving such resistors permanently connected has no effect on the operation of the device and they only cost a few cents. If you don't trust that, switching on the device after disconnecting the power supply will usually discharge the caps. Otherwise, you have to bridge the cap terminals with the resistor for a few seconds, which runs the risk of giving yourself a shock by touching both terminals of the capacitor at the same time. – alephzero Oct 22 '18 at 13:51
  • Once the car battery (or batteries) are disconnected, then using the resistor connect between the cap’s live side and earth - carefully, otherwise you get to be part of the circuit.... :) shocking... – Solar Mike Oct 22 '18 at 13:53
  • The way not to do it is to short circuit the cap terminals with a screwdriver or something similar. In extreme cases, that will produce a big spark, a loud bang, and vaporize part of the screwdriver blade - been there done that, back when I was a teenager and didn't know better! – alephzero Oct 22 '18 at 13:55
  • I’ve got a screwdriver like that :) ... – Solar Mike Oct 22 '18 at 13:57

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