Voltage on capacitors

[ppppenguin]

Electrolytics behave differently to other types of capacitors. For paper, plastic, mica etc if there's any* leakage then the capacitor is dead. If you overvolt them and they leak then for all except X rated caps you have killed them. X rated caps are designed to withstand this by blowing away a bit of foil at the site of the leak. Do it too often and the capacity drops. Common problem with capacitative droppers.

Electrolytics have to leak a little in order to work. The dielectric layer is formed this way. An electrolytic that has been used at a fraction of its rated voltage for a long time will form a dielectric layer suited to that voltage. If you suddenly apply full rated voltage then you will get grossly excessive leakage until either the capacitor re-forms or dies. Hence the need to reform NOS electrolytics. Many electrolytics are quite tolerant of short term overvoltage, for example at switch-on before valves (tubes) have started to conduct. Some types have 2 ratings - continuous and short term or surge.

*The meaning of "any" is different between ordinary radio/TV work and some precision instrumentation where ultra low, sub picoamp, leakage is needed.