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John Robertson John Robertson is offline
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Default Replacing Large Electrolytics

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.

John


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