Unused Capacitor Life?

[Killjoy99]

I've searched and can't find much.

I have come across some capacitors that have been stored for 1-2 years but have never been used. I have read that Large Electrolytic Caps such as these have a set shelf life and that buying old capacitors is never recommended. I cannot test them since I am still deciding whether or not to buy.

Should I be worried about there life span if they have never been charged? AS far as I know they were stored in the factory box so chances are the other storing conditions such as humidity and such were within bounds. Any Idea?

The planned usage is in a Solid State Power Supply as Filter caps. 100v.

[ace3000_1]

About 3- 8years shelf life for medium sized caps was the last thing i read on this matter for unused caps, typical of 25000uf and up. Basically the bigger the cap the less time they can be in an unused state.

[amb]

If left in a totally discharged state for many years, the DC leakage characteristic of electrolytic capacitors deteriorates. Sometimes a catastrophic
failure (physical leakage or explosion) may result if immediately recharged to full rated voltage. Higher quality caps tend to have longer shelf life.

Old electrolytic capacitors could be successfully brought back into specification by a process called "reforming". Search google "electrolytic capacitor reforming" for info. It's not a 100% success rate, but may be worth a try.

-Ti

[Pjotr]

Hi,

Shelf life or low load life is mainly set by the quality of the sealing for electrolytic caps. Most manufacturers specify 15 years. But in practice this can easily the double of that. Also depends on storage temperature.

But if left unused for many years the reforming issue holds. It is wise to reform trough a sufficient large resistor and measure the current. If the current doesn’t drop to a very low value (say < 1 mA) after a day your cap is gone.

Cheers

[Pjotr]

I've searched and can't find much.

Have a look here:

http://www.elna-america.com/tech.htm
http://www.elna-america.com/PDF/life-equation(12,13).pdf

[Jason Hubbard]

I have a choice of using one of two different types of capacitor. The larger is a spague compulytic made in 1982 - it was bought a few years back as NOS. I have charged a few up and they seem to hold a big charge OK, i've not checked for current leakage, but the capacitors have not leaked electrolyte and all seem to work as you would expect. I am happy to have a go at reforming them if need be.

The other is one of the "stubbies" bought in the UK Aleph-X group buy - they were made in 2000 so should have had far less time to deteriorate - there is obviously a huge difference in size for similar uf and voltage ratings.

What is the difference in use going to be between these capacitors and which should i use in my amplifiers?

[EchoWars]

Sprague made some damn good caps back then. I used a few 25,000µf 75V NOS caps in an amp I built last year. The date code was like Feb of '82 or thereabouts. I brought them up very slowly with rather large resistors to allow them to reform, and they work just peachy.