How to Test an AC Capacitor


To determine whether or not a capacitor is functioning properly, a test is necessary. Following a few simple steps will tell you whether or not a particular capacitor is performing at its rated level and will help you to troubleshoot problems in an electrical device or circuit. Having access to the capacitor's two terminals, is necessary to test it. If you notice any bulging in the body of the capacitor, or any oil leaking from it, the capacitor probably needs to be replaced, otherwise follow these steps to check its performance.

Things You'll Need

  • Digital capacitance meter
  • Capacitor
  • Read the stated value of the capacitor which printed on the housing. This value will most likely be in micro Farad (uF) and then set the dial on the capacitance meter to the next highest value setting. For example, if your capacitor was rated at 470 micro Farad, then you would want to set the dial to 2000 micro Farad so long as the next nearest value was below 470.

  • Connect the red probe from the meter to one of the two terminals on the capacitor.

  • Connect the black probe from the meter to the other of the two terminals on the capacitor.

  • Read the display on the meter. If the value is within five percent of the value printed on the capacitor's housing, it is operating correctly. If the reading is more than five percent of the rated capacitance, the capacitor should be replaced.

Tips & Warnings

  • When dealing with large capacitors, ensure they are properly discharged before handling as certain size capacitors are capable of storing large amounts of power and could become a shock hazard.

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