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How to Discharge a Capacitor Bank

Capacitors can kill you. More specifically, the charge contained within a capacitor bank --- a group of connected capacitors --- can interrupt your heart rhythm, burn right through you or even cause your tissues to explode. Admittedly, the more extreme consequences are true only with very large capacitor banks, but this is nothing to play around with. A capacitor holds charge well after it's disconnected from its power source, so you've got to discharge it to be safe.

Things You'll Need

Screwdriver with insulated handle
10- or 12-gauge copper wire
10 kohm, 5W resistor
Alligator clip
Soldering iron
Solder and flux, or fluxless solder

Instructions

- 1
  Strip the insulation from 1 inch of one end of the copper wire. Wrap the stripped portion around the metal shaft of the screwdriver, an inch or two from the handle. Solder in place. Because the screwdriver is a big heat sink, it may take a while to get hot enough for the solder to melt onto it.
- 2
  Cut the wire about 6 inches from the screwdriver. Strip that end, wrap the stripped end with one lead of the resistor and solder together.
- 3
  Cut another length of wire, about a foot long, and strip both ends. Solder one end to the other lead of the resistor. Solder the other end of the wire to the alligator clip.
- 4
  Place one hand behind your back. To resist the temptation to move your hand, you can tuck it in a back pocket or into your waistband. This step is to reduce the chances that discharge current will go through your chest if you inadvertently contact a powered terminal.
- 5
  Connect the alligator clip to ground or to the negative terminal of the capacitor bank.
- 6
  
  There's a reason high voltage equipment is protected --- and a big part of that is the energy stored in capacitors.
  
  Touch the point of the screwdriver to the positive terminal of the capacitor bank. Hold the screwdriver there 10 seconds for every 10 microfarads of capacitance.
- 7
  Touch the shaft of the screwdriver to both terminals of the capacitor bank. This is a final safety measure. This creates a short-circuit current path for any remaining charge in the capacitor.

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