[R-390] Testing mica and HV caps

[Jacques Fortin]

Bob,

The series resistor can be the DVM itself (10M ohms resistance on DC ranges is a common value).
Adjust the HV supply to the DCWV of the capacitor to be tested for leakage, then connect the DVM in series with the capacitor across the HV supply output.
If the DVM reading do not goes to zero, you have a leaky capacitor: 1µA of leakage equals to a 10 volts reading, for ex.
If the DVM reading "balances" to zero after a time (C in µF x 50 seconds), there is no measurable leakage to be concerned with (all the modern capacitors behaves like this).
Do not forget to discharge the capacitor after testing....
If it is leaky, it will discharge itself ! 

I also made a HV supply for that purpose with a small 700Vct HV transformer.
It provides up to +500 / -500 Vdc when the primary is driven by a Variac.
So caps can be tested up to 1kV DC.
500k ohms resistor in series with each + and - output prevent suicidal accidents (limit the output current at 1mA).
The HV filtering uses just 1µF, 600V caps in each leg.

This is just to test leakage, however.
Testing value and ESR requires something else...

73, Jacques, VE2JFE