Electrolytic Capacitor Lifetime and Capacitance Loss After 30 Years Storage

Do electrolytic capacitors 'age' when not regularly used?I have a project I built about 30 years ago (from EPE magazine).  A timing electrolytic cap seems to have reduced capacitance.So I'm wondering what is the 'lifetime' of electrolytic caps?Is it better I replace all the electrolytic caps in the circuit?ThanksAndy

Hi Andy-YES- Electrolytic capacitors definitely do age. It's hard to say what kind of lifetime you can expect from a capacitor.  This depends on the quality of the materials used in the capacitor, especially the electrolyte, and how close the to the maximum working voltage capacitor has been operated, also the operating temperature.Sometime you can at least partially restore a capacitor to its original specs by gradually applying voltage to it while monitoring the current.  This is known as re-forming a capacitor, and is often done when restoring antique radios. If replacing all of the capacitors is an option and it's not too time consuming or expensive, that is probably the right thing to do.-Rick    

Hi AndyAs Rick mentions above, yes they do age and that is a particular problem for vintage radio enthusiasts. Also our Audio Out column did a walk-through about swapping them for dry capacitors in audio amp circuitry.  An Electrolytic Capacitor reformer project appeared in August and September 2012 issues.-- Alan W  / EPE

Hi Andy, Yes electrolytic capacitors will aged but im not sure on the lifetime of them.  Replacing the cap would be a good route but costly.  Save money and restore what you can. 

A bit off topic but a good thing to know,  Tantalum bead electrolytics - especially older types - can go short-circuit if left for a bit.  I had some in a power supply that I did not use for a few years and when I switched it on again I got the smell of cooking transformer.  Shorted tantys were the culprit.  I replaced them and all was well.  I've read a couple of articles on this - it's a fairly well known effect it seems, so beware!

Thanks for all the replies.
The capacitor in question was in an RC timing circuit to turn off the LED display after so many seconds to save the battery.  The cap did recover a bit after a while but I replaced it in the end with a greater value.

The irony is the equipment was a capacitor meter!   From EPE December 1985.  Anyway all working now. 

Having retired I'm going through stacks of old components I've accumulated over the years, including some large caps.  And wanted to measure their values to see if they are still good.
Some Sprague 15,000uF caps are measuring around the 19,000 to 20,000uF.  I'm surprised they are over value rather than under value.  Why would that be?

Regards
Andy

Hi David,
I was going to ask if this 'ageing' process applies to other types of caps, but you've anticipated my question! 
Any other types apart from electrolytics and tants?

Thx
Andy

Andy - electrolytics typically have a skewed tolerance like -10 / +50% of nominal value because they do tend to lose capacitance over time.  Sprague is a very respected manufacturer of capacitors - now you see why!

Andy - Aluminium and Tantalum electrolytics are the main culprits for ageing.  You'll find very ew problems with non-polarised type of capacitor (polyester, mylar, mica, even the old paper ones are often just a good after years of use.

Besides electrolytics, the paper capacitors in old radios are famous for becoming leaky. Some restorers, including me, replace all the coupling and bypass capacitors on general principles before powering-up an old radio for the first time, as a leaky paper coupling capacitor can damage hard-to-replace tubes and coils. I have seen an old padder (series-tuning) capacitor develop a high series resistance: The oscillator would quit on the low end of the band. Old sealed metal-can oil-filled capacitors can become leaky in the other way: PCB (polychlorinated biphenyl) fluid leaking out, environmental hazard.

Thanks for all the replies.
My large 15,000uF Sprague caps, first time around on my capacitance meter were reluctant to charge.  IE they charged slower than they should have done.  So were measuring 2 to 3 times their rated capacitance.
On the 2nd attempt they measured much closer to their correct value.  And subsequent attempts gave similar readings.
Why did they have a charging problem first time around?
Regards
Andy

Sorry for the delay, but my hobby is restoring old synthesizers and as a matter of course I replace all electrolytic caps more than 25 years old as they can leak. A quick test is place a hot iron next to the connecting leads, if you get a small of fish, it is dead.