DIY Capacitor Discharge Probe

I am sharing a circuit I read about and trying it in the simulator. Really large value capacitors could take a long time to discharge. First, charge capacitor then switch to discharge capacitor. Battery, capacitor, and SPDT switch are to show in simulator. Probe tip is wire going from 2K ohm resistor connection to capacitor and insulated clip is where switch on bottom of circuit goes up to capacitor. 2 Lighted LEDS are used to indicate the potential remaining regardless of polarity. When they go out it indicates the cap is fully discharged. Be sure probe is well insulated. A plastic, vinyl or other insulating tube should house the probe. You could place the resistor inside the tube and use a short length of #14 solid wire as a probe end. The whole circuit could be placed inside a plastic tube for safety. Be sure to solder all connections and be sure the ground clip is also insulated. If it comes off the ground point while you are discharging, the full cap voltage will appear on the ground clip. Ouch!, or worse. The 8 diodes are 1N4000 series silicon rectifiers or similar.These diodes raise the junction of 100 ohm resistor about 3v off ground. This permits the indicator LEDs to light. LEDs are any type without internal resistor. 2K ohm resistor is for Low Voltage (up to 450 volts) For Microwave ( 5000 v caps ) ovens use 100K ohm resistor in place of 2K ohm resistor. For TV anodes use 1 Megohm where 2K ohm resistor is located. 2 Watt resistors should be adequate since current will flow for a short period of time. 100 ohms resistor is ½ watt and limits the current to the LEDs. For ground remember to use the same ground point that the capacitor being discharged uses. Simulator gives idea of time to expect for set up you choose.

published 9 years ago