How to Test for a Leaky Capacitor

Capacitors are electronic devices designed to store electrical charge. A typical capacitor --- such as an electrolytic capacitor --- consists of plates that hold the charge and a dielectric between the plates that prevents the plates from shorting between each other. However, when a capacitor ages, the dielectric breaks down and the capacitor becomes "leaky," meaning that it will no longer hold a charge and is finding a way to discharge itself --- usually through the dielectric between the plates. An expensive way to test a capacitor is with a specialized capacitor tester and oscilloscope. However, an affordable way to test for possible leakage of an electrolytic capacitor is with an analog Volt-Ohm-ammeter.

Things You'll Need

  • Analog Volt-Ohm-ammeter with test leads
  • 9-volt battery
  • Hookup wire
  • 1000-ohm resistor
  • Electronic breadboard
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Instructions

  1. Short/Open Circuit Test

    • 1

      Discharge the capacitor to be tested. A safe way to discharge a capacitor is by connecting its leads to a breadboard in a series circuit with a 1000-ohm resistor. The capacitor will slowly discharge from one internal capacitor plate to the other through the resistor in the circuit.

    • 2

      Connect the red (positive) lead of the Volt-Ohm-ammeter to the positive lead (long lead) of the capacitor. Connect the black (negative) lead of the Volt-Ohm-ammeter to the negative lead (either the shorter lead or one indicated by the capacitor labeling) of the capacitor.

    • 3

      Turn the meter's selector knob to the highest ohmic setting.

    • 4

      Observe the meter's needle pointer. If it deflects sharply toward zero ohms and then begins to drop slowly toward the infinity mark on the ohms scale, the capacitor may be good. If the needle remains at a specific resistance value greater than infinity, the capacitor is shorted. If the needle does not deflect at all, the capacitor may be an open circuit.

    Stored Charge Test

    • 5
      Observe polarity when connecting a battery to a polar electrolytic capacitor.

      Charge the capacitor with a 9-volt battery. Connecting the capacitor leads to a series circuit with a 9-volt battery on an electronic breadboard will allow the capacitor to charge up to nine volts almost immediately. If the capacitor is rated less than nine volts, use a battery that matches the capacitor's rating.

    • 6

      Remove the capacitor from the breadboard circuit.

    • 7

      Turn the Volt-Ohm-ammeter selector knob to the 10-volt setting. Connect the meter leads to the appropriate leads (negative to negative and positive to positive) of the capacitor. If the capacitor is good, the meter will indicate a charge of approximately nine volts and the needle will drop as the capacitor discharges through the meter. If the meter indicates zero voltage, the capacitor is leaky and cannot hold a charge.

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