Using an Ohm-meter to test charge a capacitor

To test if a capacitor is charging or not defective

You place an ohm meter in parallel of the capacitor and watch the ohm meter slowly increasing up into the Meg ohms. This is a good capacitor.

I think this only works when capacitors are in parallel , tied to ground like a filter cap and also the value of the capacitor has to be large?

Hi,

For a reliable solution you should disconnect the capacitor from any other circuitry. Else the circuitry may cause error in ohm reading.

Mind to discharge the capacitor before disconnecting it from circuitry / before touching it or connecting it to measurement device.. The stored energy may hurt you and/or the measurement device.

Btw. Your measurement shows only the leakage resistance of the capacitor. With large capacitors this may need an indefinite time! And additionally the resistance value depend on quality, age, size, manufacturer, type, and chemistry .... of the capacitor.
A value of 100k may be a very good value for a large electrolytic capacitor, but a very poor value for a film capacitor.

Also mind that polarized capacitors show different values with reversed connection.

Klaus

There are more problems in "easy and quick" capacitor tests like above.

1. Electrolytic capacitors, in addition to the important polarity, need a certain "formation" time under the nominal voltage during which the electrolytic process forms the nominal capacitance. Without this formation the capacitor may not show the nominal capacitance. Ohmmeters utilize a low-voltage battery that may not form the capacitor.

2. Some capacitors are not designed for a low internal resistance. Their charging/discharging time in series with a resistor may imply a high capacitance but really it may not be true. For instance, "flash" capacitors are specially designed for a fast charge/discharge. If you use an ohmmeter, such capacitor may still hold a charge and burn your ohmmeter.
3. For testing, separate the capacitor from other circuits and discharge it. Then find a similar-value capacitor and connect one after another to your ohmmeter with a correct polarity (negative lead from Ohmmeter becomes positive in this test), bet with a series resistor like 1...10 kOhms. Record ohmmeter indication over time (ohms/sec.). Test your known good capacitor the same way. If both give a similar charging pattern, both may be good.

A multimeter is not really a very good tool to use to check capacitors though, as the capacitor could be bad, but still exhibit normal looking behavior on a multimeter. Usually you want to use an ESR Meter or capacitor function meter to check capacitors

Edit: to test the capacitor you need to remove it from the circuit even with ESR meter

My ohm meter uses only 0.2V to measure Ohms so it does not cause a silicon junction to conduct. Then it is almost useless to test a capacitor for leakage.