In a car, locate your battery in the engine bay or trunk, then loosen the nuts holding the cables on the negative (-) and positive (+) terminals using an open-ended wrench or socket with a ratchet. Slide the cable off of the terminal to disconnect it. Wrap the end of each cable with a rag so they don’t touch anything. In your house, you can usually unplug the device you’re working on from the wall, but if you are unable to do so, locate the house’s breaker box and flip the switch that controls the flow of electricity to the room you’re working in.
Setting it to the highest possible setting will ensure you get an accurate reading of however many volts of electricity the capacitor is charged with.
You may need to open your appliance or remove components to gain access to the capacitor. Refer to an application specific repair manual for help if you can’t locate or access the capacitor. Touching both leads to the same post will not produce an accurate reading. It doesn’t matter which lead you touch to which post because it’s reading the level of current passing from one to the other.
If the capacitor reads as having fewer than 10 volts, you don’t need to discharge it. If the capacitor reads anywhere between 10 and 99 volts, discharge it with a screwdriver. If the capacitor reads in the hundreds of volts, the safest way to discharge it is with a discharge tool, rather than a screwdriver.
If you touch the two posts, or accidentally connect them with a tool, you could get badly shocked or burned.
If you are unsure whether or not your screwdriver is insulated, it’s best just to buy a new one. You can purchase insulated screwdrivers at any auto part or hardware store, as well as at most large retail stores. It does not matter if the screwdriver is a flat head or Phillips head.
Purchase a new insulated screwdriver if the handle on yours is damaged. You don’t have to throw a screwdriver with a damaged handle away, just don’t use it to discharge capacitors or do other electrical work.
Maintain a comfortable grip. There’s no reason to squeeze the capacitor too hard. Keep your grip low on the capacitor to avoid contact with sparks when you discharge it. Use a pair of insulated pliers to hold smaller capacitors so you don’t accidentally shock yourself while you’re discharging it.
You will hear and see the electric discharge in the form of a spark. Make sure the screwdriver is touching both terminals at once or else it won’t work.
This step is just a safety precaution. Once you’ve confirmed that the capacitor is discharged, it’s safe to handle. You can also confirm that it has been discharged using your multimeter if you’d prefer.
The alligator clips make it much easier to keep the tool connected once it’s completed. You will also need electric tape or heat shrink wrap and a soldering iron if you don’t already have one.
Each wire just needs to be long enough to connect one end of the resistor to one post on the capacitor. Cutting the pieces a little longer gives you some extra slack to work with and may make things easier.
Both ends of both wires should show bare metal now. Make sure to remove enough insulation to solder the stripped ends to other wires or clips.
It should now look like a resistor with long wires sticking out of each end. Leave the loose ends of each wire free for now.
If you use heat shrink wrap, you can shrink the wrap in place over the connection by exposing it to the flame from a lighter or match. Do not expose electrical tape to a flame.
If you are going to use heat shrink wrap, remember to slide it over the wire before soldering the clip into place; otherwise, you won’t be able to get it over the head of the clip once it’s permanently affixed to the wire.
Be sure each clip has a clean connection with the metal of the post. Be careful not to touch the posts with your hands while you connect them.
If the voltage doesn’t drop, one of the connections isn’t right in the discharge tool. Examine it closely for where one might be broken. Once all of the connections on the discharge tool are good, try again and it should discharge.
