×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Shelf life of electrolytics

Shelf life of electrolytics

Shelf life of electrolytics

(OP)
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.

RE: Shelf life of electrolytics

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
www.gke.org

RE: Shelf life of electrolytics

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.

RE: Shelf life of electrolytics

(OP)
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.

RE: Shelf life of electrolytics

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!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources