Testing leakige on electroulytic cap

I am looking for a project to test leakige of electroulytic caps.
Can you help me.

Hi Gregory,

I usually charge the cap to a defined voltage and let it rest for a while. Measuring the voltage at regular intervals using a very high impedance voltmeter I plot a curve.

If it keeps moving downslope I forget about the cap.

Boncuk

Hi Gregory,

If these are old ones, they can usually be re-formed.
Stick a current limiting resistor in line, and put it on charge.
I normally start at very low currents, with a meter in line for monitoring.

Electrolytics do leak a little anyway, but not normally enough to run warm,
unless they are intended to run at more than a few hundred volts.
Old types running at over three hundred volts would be expected to be warm
to the touch, but not actually hot, that would mean excessive leakage and
time to investigate.

They are chemical units and the leakage changes with the applied voltage so
you cant just treat it like a resistor.

If these are quite low voltage caps like for small transistor stuff, just
hold a little nine volt battery in series with a hand held voltmeter on ten
volts, and see that the reading drops. It wont stop reading completely,
cos they all leak a bit anyway, even new ones.

Best of luck with it, John

When you charge a Cap do you charge it with 25 V DC with a low current say 1 Amp.
Testing a 250 V cap 220 uf
If I only have a DMM do I have to insert a Resistor in series to read the voltage. If the voltage is high.

Gregory said:

When you charge a Cap do you charge it with 25 V DC with a low current say 1 Amp.
Testing a 250 V cap 220 uf
If I only have a DMM do I have to insert a Resistor in series to read the voltage. If the voltage is high.

Click to expand...

while using dmm and high impedance meters, no use of series resistorunless it reaches 100Mohms.
iJust imagine the impedance of DMM in DC Voltages ranges,and compare your seires resistor that is proposed. Just of no avail.

Charge the capacitor with the voltage you intend to run it at.

Connect a large series resistor, measure the voltage across it and calculate the current using Ohm's law.

You could actually use a multimeter as the series resistance. If you know the input impedance then calculating the current is easy.

Also note that the leakage current depends on the voltage you charge it to. You can build a circuit that does all of this automatically if you like but you need some way of providing a suitable variable voltage possibly as wide as 3 to 500V depending on what you want to do.

Hero999 said:

Charge the capacitor with the voltage you intend to run it at.

Connect a large series resistor, measure the voltage across it and calculate the current using Ohm's law.

You could actually use a multimeter as the series resistance. If you know the input impedance then calculating the current is easy.

Also note that the leakage current depends on the voltage you charge it to. You can build a circuit that does all of this automatically if you like but you need some way of providing a suitable variable voltage possibly as wide as 3 to 500V depending on what you want to do.

Click to expand...

Yes Hero999, I got a point . Thanks