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~misfit~[_3_] ~misfit~[_3_] is offline
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Default Replacing Large Electrolytics

Once upon a time on usenet John Robertson wrote:
On 2018/08/25 11:23 AM, Cursitor Doom wrote:
On Sat, 25 Aug 2018 10:39:13 -0700, John-Del wrote:

Heat and charge cycles do affect a capacitor's life, but they're
not the only factors. Humans who smoke, drink, and do drugs have a
shorter life than those who don't, but we all will die eventually.


Hmmm. Not really a valid analogy!

I've had plenty of electros in stock go off value, become leaky,
and go up in ESR just from sitting in a nice quiet bin. I don't
install any cap without running through my Z meter, and I will toss
an entire lot of caps if one is bad.


I managed to find 8 electros in my bin that could used in parallel
to get the equivalent of the failed ones I've removed. I've checked
them all for ESR, leakage and Capacitance and the readings I've got
have come out indistinguishable from new caps of the same value &
voltage rating. I've picked the best 6 (with the lowest ESR) and am
re-forming them over the course of this weekend.
I'll report back in due course on the success (or failure) of this
method. I certainly wouldn't want to hit them with their rated
voltage straight away after so long in limbo as that *would* be
inviting disaster.


The final test is leakage, set the cap up with an ammeter in series
and put it on a power supply running around 75% of the rated maximum
voltage. Leakage should be very low after the cap has stabilized.

Here is a nice write-up:

https://www.nmr.mgh.harvard.edu/~reese/electrolytics/

Heathkit made a great cap checker that we use to check older off the
shelf NOS caps. Has the Magic-Eye tube and everything - except ESR.


Thanks for that link.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)