jj@rabbit.UUCP (10/19/83)
Electrolytic capacitors do indeed require a polarization voltage when they are first used, however, most cap's are "formed" at the factory, and will not have outrageous leakage when you turn them on, unless they've been out of use for a long period (a typical half life for an electrolytic coating is 6 months.). If the capacitors do need to be formed, the "right" way is to limit the leakage current, and let them form slowly, which is not what happens when you turn on your amp. As an aside, whenever you turn on your amp (or anything with semiconductor rectifiers in it) you charge the filter capacitors VERY QUICKLY, typically a normal 35 volt supply's inrush current will be on the order of 100 amps for one half cycle of the AC line, and 25 amps for the next half cycle. This surge is what makes your lights dim, and your TV shrink when you turn on your amplifier. Some amplifiers do have surge limiting built in, especially higher powered amps (they have a disproportionally large inrush current for reasons that I will momentarily skip.), but most amps just use a large rectifier <they're dirt cheap> and let the surge happen. This surge is indeed hard on both rectifiers and capacitors, which is a good reason not to turn you amp on and off a lot. (Independant of other considerations.) If your amplifier has been off for quite a while, I would suggest putting a commercial (UL approved, etc) surge limiter in series, and starting it up with the surge limiter in circuit. That way, if the electrolytic cap's have depolarized, you will limit the current through the breakdown points. <When a capacitor depolarizes (as opposed to drys out, another, much slower mechanism) the capacitance goes UP and the breakdown voltage goes down. Problems usually arise only if the supply voltage is lower than the breakdown voltage of the deformed cap, which is an unusual occurence.) Capacitors usually have a safety factor of 2-3 built in, with additional depolarization protection in the form of a permanently anodized layer on each foil. Anodizing is the same process as polarization, but the rate of loss varies with the material. -- O o From the pyrolagnic keyboard of ~ rabbit!jj -v-v- \^_^/ (pyrolagnic- from pyro<=>fire and lagnic<=>eating.)