Capacitor voltage leak??

[MagicSmoke]

While in circuit and powered on should a capacitor ever have voltage to the metal can that contains it??

I have 2 220uf 25v caps on an X main board that have 60v when probe is touched to the X vent. None of the others of that voltage and uf have any volts to can.

Are they bad?? Neither one is bulging. Thanks.

[mariushm]

Re: Capacitor voltage leak??

The voltage written on the case of a capacitor is the maximum voltage the capacitor can tolerate before it becomes damaged.

The metal case of the capacitor can sometimes be isolated from the capacitor, but it's often "connected" to the negative lead (not on purpose, just a consequence of how a capacitor is built).

Therefore, it's best to measure the voltage between the two leads of the capacitor, not between one lead and its case, or one lead and the metal chassis.

I suspect you measured 60v incorrectly, because of different grounds (maybe you put the probe on chassis or the monitor).

You can't really tell that a capacitor is bad or not by measuring voltage. Even measuring capacitance is not a good way to check a capacitor - it's quite possible to measure the capacitance with a multimeter and see the expected value but the capacitor can still be bad when you actually power up the circuit.

Proper measurements can be done using LCR meters or ESR meters with the capacitor removed from circuit.

[MagicSmoke]

Re: Capacitor voltage leak??

I did have ground probe on chassis, readings of 60v to can are not incorrect, these are on an X main plasma board which is grounded to chassis.

3 others of same V and uf have no volts to can. Nor do any of the other cap's on this board (2 100v 220uf and 5 250v 150uf) caps.

That's why I was curious about reading.

Board is supposed to be outputting 58v DC and -198v DC its input voltage is 211v DC.