DIY Standalone Capacitor Meter

• You can build a standalone capacitor meter and make it an integral part of your test bench equipment. Check your spare parts box for the following components, starting with a low current 280 volt center tap (VCT) transformer. The schematic provided indicates an on/off switch in a fused primary and another switch in the secondary to change to different applied voltage taps. The simple power supply has a rectifier and filter with a bleeder resistor and a 10 meg ohms resistor in series with a 50 uA meter. The unit can be made portable by mounting components in a small plastic box.
  
  Mount the meter face on the front of the box along with switches clearly marked. Mount the transformer and all other components hardwired and soldered around the mounted items. Convenient test leads can be coiled and held to the case with a spring clamp. Another option is to mount the tester into your bench at an easy access location.
  
  

Testing Method Using the Capacitor Meter

• Disconnect one end of the capacitor from the circuit. Set the voltage switch to the high (400 VDC) or low (200 VDC) range. Apply voltage across the test capacitor. It will indicate a high voltage momentarily then fall to zero. Using the 10 meg input resistor, a .1 microfarad capacitor should take eight seconds to go back to zero. If it fails to kick, either the capacitor is open or it is too small to provide the kick. The low limit here is a .01 microfarad capacitor. This limit depends on your meter's response speed. If you have a small fast-indicating meter, the range may go as low as .0025 microfarad.
  
  If the capacitor is shorted, then it will register the output voltage of your power supply and stay in that position. Usually a bad capacitor will show a leak. Initially it will kick and then fall back toward zero and never return to that point. This indicates the capacitor is passing direct current and has failed.