Surplus caps how old is too old?

[woody]

In cleaning out my garrage I found a box of electrolitic caps I had
bought back in 1980. They seem to still be healthy but is there any way to predict how long an old cap like this will last if put to
use. When charged up to their rated voltage these 15,000uf 63v
Marcom caps didn't seem to have any leakage current to speak of
and held a charge for a few hours when disconnected. I have 20 of these I would like to find a new home for but don't want to sell
anything that is likely to fail real soon.

Thanks for past and future help,


Woody AKA bob12345678

[tiroth]

You could test the ESR. I believe a major failure mechanism is aging causes a rise in ESR, which causes higher dissipation, faster aging, etc.

[Peter Daniel]

I like surpluss caps too. Check my other thread dealing with that matter: How long electrolytic caps last?

[yeti]

Usually they should still be ok,but possibly the dielctric must be reformed.
To do so ,you can connect a variable power supply to the caps in series with an ammeter, now increase the voltage to 1/3 of the maximum voltage of the caps.
At the beginnig there will be a certain amount of leakage current that decreases after a while, if the leakage current is below 1 mA you can slowly increase the voltage applied.
If you reached Vmax * 1.2 at a reasonable leakage current the caps should do for te next 10 years.

regards; Arne