[sdiy] Electrolytic capacitor life

[ASSI]

On Monday 15 August 2011, Dave Kendall wrote:
> A few years back I got many unused electro caps amongst other things
> from a clear-out of a broadcast maintenance department that was
> closing-down. I have heard that electro caps "dry out" over time. These
> particular caps are probably around 10 - 20 years old.
> 
> Are they any good? Recently I found and rejected at least one cap that
> measured well below its rated capacity.

If they've never been used and stored properly most of them are probably 
still OK, but don't expect them to still be within spec and I wouldn't use 
them in an application where the reliability might be key.

> I guess someone here has some real-life info on electro cap ageing.

They can dry out and they're dead when this happens.  If you measure much 
less capacitance than new, this is a good sign that you probably shouldn't 
use them.  The other thing that electrolytics like to do is losing their 
"forming" and this means that they will leak a lot more than they should and 
do not handle the rated voltage well.  If they are otherwise OK, you can try 
and re-form them by slowly ramping up a voltage on them while measuring the 
current until you get to the rated voltage (or a bit on top of that) and the 
leakage current goes down to normal.  Or you just charge them through some 
MOhm resistor (for each cap individually) and monitor the voltage drop over 
that resistor.  After they've been taking well to the top voltage for a day 
or so and aren't leaking any more, if you really want to make sure they're 
good you would need to check their series resistance with an AC voltage.

New electrolytics are usually cheaper and safer to use than doing the above, 
YMMV.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf microQ V2.22R2:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada