19 Jan
2012
19 Jan
'12
7:41 a.m.
On 1/18/12 9:50 PM, "Eric Smith" <eric at brouhaha.com> wrote:
Rob Doyle wrote:
I've cited this research before in this thread, and it states that the
common failure mode is that the equivalent series resistance (ESR)
increases, which contributes to other failure modes. "The wearout process
is rarely driven by
evaporation and escape of the electrolyte unless the safety vent is
compromised due to high leakage current and pressure buildup."
Overvoltage is not likely to be a factor in an existing system unless
there has been some other failure in the power supply, in which case you
have other things to worry about, too.
http://www.cde.com/tech/reliability.pdf
These are the people who *make* these things. I think they probably have
some insight here.
It seems to me that you'd need to understand
the failure
mechanism to build a monitor for it.
You don't need to understand the failure mechanism of a component to
monitor for the failure. You only need to understand the observable
behaviour of a failing component.
Nevertheless, the failure mechanisms of aluminum electrolytic capacitors
are well understood. Three of the most common are:
1) oxide breakdown - when not under bias for an extended period, the
oxide breaks down, which reduces the safe working voltage of the
capacitor. At lower voltages, the capacitor appears to be more leaky
than it should be. This can be fixed by reforming the capacitor.
2) catastrophic breakdown - when the applied voltage exceeds the safe
working voltage (which may be reduced from factory spec due to oxide
breakdown), the capacitor will short out in a spectacular manner.
Non-repairable.
3) electrolyte drying out - this happens if the seals are bad, or if
the capacitor is overstressed and ruptures the seals. Non-repairable.
It is as-if the capacitors initially shorted for
a while,
and then opened...
Sounds like it had oxide breakdown, which then resulted in catastrophic
breakdown.