How to confirm AC power capacitor OK?

Question

How to confirm AC power capacitor 100% OK?

For an example a 200uF 250Vac power capacitor,

I have came across by using multimeter to check its uF,resistance eventhough is ok,but when putting it to the unit,it didn't work.

Any other methods can confirm it is 100% ok?

Answer 1

You could put it in series with an inductance and measure the AC voltage drop across it.

At 60Hz, Xc = 1/wC = 1/(2*pi*60*200e-6) = 13.26 Ohms reactance.

Whereas, XL = wL = 2*pi*60*L

so for a 2 Henry inductor, you'd get XL = 754 Ohms reactance.

Thus, in series, you'd expect to see about 2 volts on a 110volt line.

Answer 2

Connect it to the mains then remove the power and see if it still measures voltage. It should hold voltage for a while unless its bad. If it has a discharge resistor inside it, then you may have to be quick. A resistor symbol on the side will tell you. You can also measure the current while its connected to the mains. You will have to work out the impedance to know what it should be at whatever frequency your mains is.

http://pr.erau.edu/~newmana/imped.html

Be careful connecting to the mains. Do it through a switch with a fuse in case the thing is short as many fail short.