Shelf life of electrolytics

[Dryjoint]

Hello all. I've been offered a quantity of 63V 6800uf caps, but the're date stamped 1996. I vaguely remember being told that the electrolyte degrades, or that the working voltage decreases if they're not charged regularly. This was in 1976, so whilst the technology has, no doubt improved, is this still the case? Thanks, Steve.

 

[Skogsgurra]

They may need to be reformed. At least if you are going to use them in a high-power application.

What happens is that the Al2O3 isolating layer on the electrode's surface deteriorates. By letting them work at a reduced voltage and with a limited current, you can "rebuild" that oxide layer. It usually takes several hours to do it. Connect via a resostor to about half the working voltage. Make the resistor low ohms so that the initial leakage current doesn't consume all the voltage.

Gunnar Englund

http://www.gke.org

 

[rtronics]

Hello Steve,
Reforming electro's went out of fashion when manufacturers started making ones that don't spill when they are tipped over.
Provided that your ones have been stored within man's specs, they will be as good as new.
OTOH, putting 10 YO electro's in new equip't will be noticed, to the detriment of reputation.
Regards, Ray.

 

[Dryjoint]

Thank you both for your information. Whilst it's not for commercial use (wind generator charge controller), and I'd quite happliy nurse them back to full capacity, for this application I think I'll let these ones go, as I do need reliability. Thanks again.

 

[eeinpa]

About 15 years ago I worked for a large industrial controls company which had dealt with a MAJOR field problem involving deterioration of electrolytic caps in power supplies. It cost them a lot of money, and they forced themselves to learn a lot about these caps. My understanding (I came on board after the problem) was that the primary problem is loss of electrolyte. As temperature is increased, the rate of electrolyte loss increases in a very predictable (and exponential) manner. I was told they could get a customer's operating conditions and predict the failure date of the caps to within a month or so. In work I have done since, it still appears that the limitation with electrolytic caps is electrolyte loss due to heat. The bottom line is, if the bargain caps you mention were stored under reasonable conditions (i.e. "room temperature") they are probably fine. If they were stored in an overheated spot, you may be in trouble. If you primary concern is reliability, I'd keep looking!

 

[TurboXS]

This may help;

http://electrochem.cwru.edu/ed/encycl/misc/c04-appguide.pdf

regards
Peter