Capacitors store energy inside a device for use as a dedicated power supply to a particular system. A car uses a capacitor to power an alarm, so the capacitor is drained of power instead of the battery if the alarm is not shut off. A capacitor can be tested with an ohmmeter or a multimeter to determine if it's functional or shorted out. An appliance or system that's not working properly may only need a new capacitor.
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Things you need
- Insulated screwdriver
Discharge the power supply stored in a capacitor prior to testing with an ohmmeter. Touch both terminals on the unit with a metal screwdriver that has an insulated handle. The connected circuit formed by the screwdriver blade against the terminals will drain the power. Unscrew the terminals and remove the wires.
Set the ohmmeter or multimeter for testing. Set a multimeter to an ohm setting in the high range. Turn the meter on, touch the leads together and set it to zero with the calibration wheel.
Touch both terminals with separate meter leads. Watch the needle motion. The needle should swing to the right a couple times and then rest on the infinity mark on the left.
Reverse the leads. Remove the ohmmeter leads and place them on the opposite terminals. The needle will swing to the right again before resting on the infinity mark if the capacitor is good. The needle will drop to the zero mark on the right if it is shorted out.
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