I have a completely discharged (when I got it there was a paper clip between the posts) 120v capacitor. It is the same (physical) size as the capacitor my brother is currently using between his battery and amplifier in his car. I would like to know if I can charge this capacitor off my car battery and use it for my amplifier. I assume that it will only charge to the voltage I apply to it, but I would like to have an expert advise me on it before I try ( I'd just as soon not cook my amp). It says nothing about Farad capacity on it just the 120v designation. Thank you for any help you can provide.

sclark

Technically, it all depends. However, as a general rule, the answer is a very large no. Unless they are the same amplifiers, used for the same purpose, with the same sized (capacitive size, not physical size) capacitor, it could cause some severe trouble.

The capacitor itself would only store a potential up to the voltage that you put across it. However the capacitance of the capacitor (the Farad value) when combined with the other elements of the circuit cause different time constants and discharge at different rates.

For a series RC circuit (using your cap against a load);
VR = Vo e-t/RC
If C decreases, the time constant 1/RC increases.
This means that the voltage change happens much quicker. The passing of charge at a quicker rate means that more current is flowing through the rest of the circuit. This is liable to damage a circuit.

Simply,
1) Find out the capacitance required for your amplifier
2) Find out the capacitance of the cap you have
3) Only replace the desired cap with the one you have if you are SURE that they won't damage each other.