How Do I Check to See If a Capacitor Is Still Good?

Written by skip shelton Google
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How Do I Check to See If a Capacitor Is Still Good?
Multimeter tools measure resistance. (Polka Dot Images/Polka Dot/Getty Images)

A capacitor stores energy in two plates separated by an insulator. Capacitors smooth electricity by providing a steady, uninterrupted stream. Capacitors also provide electrical discharges at voltages far beyond the incoming electrical feed. Appliances, computers, digital cameras, guitar amplifiers, televisions and many other electrical devices use capacitors. Failed capacitors cause electrical shorts, part failure and erratic device behaviour. Visibly damaged capacitors require replacement. Test capacitor functionality with a multimeter measuring resistance. Always discharge capacitors before testing to avoid electric shock and enable accurate test results.

Skill level:
Moderately Easy

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Things you need

  • Insulated wire
  • Insulated screwdriver
  • Electrical safety gloves
  • Multimeter tool

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  1. 1

    Remove the electricity from the device to be tested. Turn off the device, pull the electrical plug, and remove any batteries powering the device.

  2. 2

    Discharge the electricity stored in the capacitor. Two leads protrude from the capacitor. Touch these wires with a thick wire or metal screwdriver to bleed off electricity. The thick wire or metal screwdriver acts as a resistor and drains the capacitor's electrical charge. Do not grasp the wire or screwdriver by the metal. Wrap the wire in electrical tape, hold it by the insulation, or use electrical safety gloves. Grasp the screwdriver by the insulated handle.

  3. 3

    Hold the wire or the screwdriver against the two electrical leads for at least 30 seconds. Capacitors with wires protruding from the sides, instead of the bottom, require bending of the wire to touch both leads simultaneously.

  4. 4

    Adjust your multimeter tool to measure Ohms. The Ohm setting is often indicated with the Greek symbol Omega. Omega is shaped like an upside-down horseshoe.

  5. 5

    Touch the red-and-black multimeter leads to the two leads protruding from the capacitor. Each multimeter lead touches only one of the capacitor leads. Monitor the output on the multimeter tool. The multimeter's battery, when both leads are touching the capacitor, charges a good capacitor until the electrical charge is at its maximum.

  6. 6

    Determine if the capacitor is still good. Good capacitors read zero initially on the multimeter tool. The resistance measurement slowly climbs to infinity without stopping.

  7. 7

    Identify failed capacitors. Failed capacitors in an open state fail to produce a reading on the multimeter. Electrically shorted capacitors do not store charges and only read zero. Leaking capacitors initially read zero and climb toward infinity but stop as charge begins to leak from the capacitor.

  8. 8

    Replace failed or visibly damaged capacitors.

Tips and warnings

  • Visible damage to capacitors includes broken prongs, bulging, gel leakage and extreme corrosion.
  • Before replacing leaking capacitors, as measured on the multimeter tool, verify the expected behaviour by measuring a known good capacitor. Some capacitors do not reach infinity in a functional state.
  • Fully discharge capacitors before handling. Charged capacitors are hazardous.

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