Diy capacitor leakage tester

[diydidi]

Hi
I want to build a capacitor leakage tester/ checker instead of buying something expensive.
I was thinking of using my variac, followed by a voltage doubler to reach about 700V DC.
I'm not sure how to do the metering. I could either use a 50uA moving meter in series with a 10k resistor followed by the cap under test, or I could measure the voltage across the cap instead of the uA meter keeping the series 10K resistor.
I'm open for ideas and if any one has a better layout, please share it with me.
Thank you!

[nickb]

My test is very pragmatic. Put voltmeter across power B+. Remove all the tubes (except the rectifier) and power up then off and observe how quickly it partially discharges. The leakage current = total capacitance X change in voltage / time. While power is applied you can also measure the drop across any dropper resistor to see what is happening further down the chain if you need to isolate. You may need to subtract any current through discharge / balancing resistors if any.

For non psu caps any leakage usually just shows up as a voltage somewhere it should not be.

I never built a leakage tester as it would require the cap to be removed. If I'm going to do that I might as will put in a fresh one and save the test time.

If your heart is set on it I think there are two methods. (1) Charge and then measure the discharge rate - no use for small values or (2) Adjust the variac to get a steady voltage on the cap then measure the current through it. Don't forget to protect the meter from overcurrents. And don't forget an isolating transformer.

[Enzo]

If you want to test loose caps, find an old Heathkit or Eico capacitor tester, they work great. I built an Eico 950B about 55 years ago or more, and I still use it.

In circuit, I have never needed a cap tester, as I can tell the health of a cap by its performance in the circuit. As nick said, a coupling cap should block all DC, if it doesn't, it's bad.

[nickb]

Here is the Heathkit C3. It's based on a bridge. Does capacitance, leakage, power factor and resistance too.