How to Test a Leaky Capacitor

1. For checking lower values, C2 can be reduced to say 100 pF or 1000 pF. The blinking rate being a function of the value of C2 and leakage resistance of test capacitor, it becomes faster and is thus more convenient to test high . valued capacitors. Similarly, quality of non-electrolytic capacitor C2 must be better than of the capacitor under test, to give correct indication of leakage of V test capacitor. Otherwise, after completion of initial charging of capacitor, the effective voltage across the neon lamp may not be sufficient due to potential divider action of their relative leakage resistances,
2. When testing a leaky capacitor the actual blinking rate is a function of both the leakage resistance and capacitance value. For example, a 2ptF capacitor with I0 megohms shunt leak under test produces a blink every few tens of seconds. Therefore, while testing capacitors observe the initial glow to get an idea of the capacitance value and wait a minute to watch for any leakage.
3. he tester works well with all low leakage type capacitors such as poleyster, polystyrene, ceramic, mica, and paper. All types of non—electrolytic capacitors can be connected across the test probes without observing any polarity restrictions. While testing electrolytic capacitors, the positive terminal of capacitor should be connected to the red test probe and . negative terminal to the black test probe. These terminals should not be reversed. And since the leakage resistances are generally of the order of one megohm only, the value of capacitor C2 is to be suitably increased to reduce the blinking rate so that it will be convenient to identify leaky capacitors.
4. The test capacitor value should be one order higher than the value of C2, for correct results. Otherwise, when initially both capacitors are charging together in series, the effective voltage across the neon lamp may not be sufficient to show`the initial blink because of the voltage divider action of the relative capacitive impedances.  ln the present circuit 0.0l;J.F (10,000 pF) is used for C2 so that a little higher value test-capacitors can be easily evaluated.
5. A leaky capacitor may not be indicated properly by the neon lamp’s blinking. T V The neon lamp can be any common type meant for pilot lamp on 230V AC. lf its firing voltage is lower, it serves V better and improves the test range toc. Since the tester operates directly on AC/mains, utmost care must be taken to·avoid electric shock. Correct live and neutral wire connections are shown for better safety. Even after turning off power, some stored charge in smoothing capacitor Cl remains for quite some time. So short circuit the test probes after removal of power by turning switch Sl into test position, before handling.
6. With a little experience and practice, the results can be made very effective. V This tester has more uses such as continuity tester.

How to test a leaky capacitor is shown below: