On
10/07/2010 03:15 PM, Richard wrote:
Yeah, but this isn't what occurs when you
just power on the device.
Actually, it is.
No, it isn't. The part you
didn't quote is where the other poster was
saying "apply increasing voltage gradually". That's what you do when
you reform a cap. Its *not* what happens when you turn on the power.
Otherwise people wouldn't need reforming circuits.
The specific context was a device that's been powered off a relatively
short time. The oxide has only deteriorated a small amount, and not to
less than the working voltage. Powering it up, at the working voltage,
will do some reformation, and will no damage the capacitor.
I never said that this procedure was applicable to capacitors that had
been powered off for a long time; in fact, I think I specifically said
otherwise.
I described a different procedure for capacitors that haven't been
powered for a long time, which involved limiting the current into the
capacitor. Limiting the current has the effect of not allowing the
voltage to increase beyond what the capacitor can handle (assuming that
you chose the current limit appropriately). This is actually much
better than ramping the voltage at a constant rate, because the
capacitor make take longer for reformation during some points in the
process than during others. We saw that with some capacitors in the PDP-1.
Despite that, it is still the case that reformation is what is occuring
in both scenarios, which is what I replied "actually, it is" to in the
quote above. It is the same electro-chemical process; you seemed to be
claiming that it was not.
Eric
