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electrolytic capacitors shelf life

electrolytic capacitors shelf life

electrolytic capacitors shelf life

I have found that electrolytic capacitors only have a shelf life around a year. By not being used they degrade and read out of spec.

I purchased a large assortment of caps and found many are reading low when tested. I have herd of reconditioning but finding conflicting info on how best to do this.

I would like to make a simple bread board style reconditioning device that I could just plug in dozens at a time to keep them fresh.

So what would be the best voltage to do this at as a percentage of the cap rating, What kind of current limiting is recommended, and a time length to do this?

RE: electrolytic capacitors shelf life

A one-year shelf life? Those must be the worst ever 'lytics. If you purchased an "assortment", I have a feeling you either purchased used/recovered or you purchased old lots that were dropped many years ago.

You cannot recondition a cap that has dried out... it's not a battery that has grown tin whiskers, it has lost an important part of its chemistry.

Dan - Owner

RE: electrolytic capacitors shelf life

No they are all brand new name brand caps unsoldered with untrimmed legs. Without exercise caps loos their charge i.e. "charge capacity" Just like old NiCad batteries they develop a "memory" to the discharged state. Not dried up just in need of something like a deep cycle for NiCad batteries to regain full capacity. I figure I got a good price on 1 to 2 year old stock because they were "stale" caps. Installing an old cap that has not been used for too long can explode the first time they are powered up by trying to charge them too fast due to reduced capacity. Basically these type of caps over long times of being unused loose the capacity rating. For instance a cap with a 320uf rating over a couple of years will measure only 220uf when tested and given enough time will just read a shorted condition. By cycling one of these slowly they can recover to their brand new state.

RE: electrolytic capacitors shelf life

By the way,
"Love your user name" LOL

RE: electrolytic capacitors shelf life

The traditional approach is simply to apply voltage to them, as normal operation (not maximum rated). In extreme cases where you might have readon to be nervous, perhaps slowly increase the voltage.

Old (vacuum tube) radios that have been in storage for years or decades are sometimes powered up with a 100w light bulb in series with the AC power. Or they might use a variac to bring the AC voltage up slowly. Of course, expecting to replace the failed caps along the way.

One year seems a bit poor. But you did write 'out of spec' as opposed to failed. How did you 'read' them?

RE: electrolytic capacitors shelf life

Typo: ...reason to be nervous...

RE: electrolytic capacitors shelf life

A constant DC voltage source and a current limiting resistor in series with the capacitor is all you need. Size the resistor assuming the capacitor is shorted and you don't want to burn-up the capacitor or resistor. If the capacitor is good it will charge to your supply voltage.

RE: electrolytic capacitors shelf life

VE1BLL seems just as confused as me with no facts or proven answers.
My out of spec description can mean anywhere from 5% to 35% in my case on the caps I have tested.

Current limiting and volt rating seems to be key factors here with my research. Yes buying a brand new name brand replacement cap for a one time repair is the best way to go. For those like me who have only need to deal with an electronic repair once in around 5 years like me would like to know this. I had very few new caps from 15 years ago that were good but now test bad. I have pitched them all in the trash they were not the size I needed anyway. I have bought an assortment lot of over 2500 pcs so I don't have the wrong size ever again. Now I am looking for a way to keep these in serviceable condition for my lifetime. Looking for "expert advice" with proven and documented results.

Not looking for guesswork here we are looking for not easily found info on the internet with before and after results.

RE: electrolytic capacitors shelf life

Quote (OP)

...with no facts or proven answers.

RE: electrolytic capacitors shelf life

This is just an example of cap conditioning I have found. Note that this is for very large caps and not very detailed. Useful for the application yes but not a good "rule of thumb" for all caps like this.

RE: electrolytic capacitors shelf life

The purpose of Eng-Tips is to provide answers and advice, not proof. If you want proof, you'll have to satisfy yourself through your own efforts. Nobody here has any obligation to provide proof. First of all it's too much effort to try, secondly it's impossible to "prove" anything via the Internet (ref. famous Dog cartoon, or any conspiracy theory you wish).


The video you linked is exactly what I mentioned in the sentence in my post containing the word "variac". The approach also applies to electrolytic capacitors of the type used in (old) radios.

Besides applying voltage, what other possibilties come to mind? What else can one do to a capacitor? Perhaps there's an optimum storage temperature. What other possible actions are there? Anoint them with oil? smile Play classical music to calm them? smile Joking aside, there's only the terminals to work with, so what other possibilities are there?

RE: electrolytic capacitors shelf life


"My out of spec description can mean anywhere from 5% to 35% in my case on the caps I have tested"

Well, look at the specs of an ordinary electrolytic capacitor. -10% and +50% are standard specs and from -20% to +80% has been heard of. So, your capacitors do not seem to be seriously out of spec. Not at all, in fact.

Another important thing is how you actually measure the capacitance. Tou can use a multimeter with C range or you can use a low voltage (a few hundred millivolts RMS) pure sinewave and measure the resulting current. If you use more voltage, the reverse voltage will do things to your capacitor, but as long as you are Belov half a volt peak, this method works.

The best method for electrolytic capacitor is the charge/discharge metod. Apply a DC voltage via a resistor and record charge time (63.2% of final voltage and final voltage. The C can then be calculated from T/R, where T is charge time. The final voltage will tell you if there is excessive leakage or not. If final voltage (after 5-10 T) is very close to the supply voltage.

It is a good idea to then set the supply voltage to zero (not just shut off, short circuit the source) and record the discharge time. It should be the same (or a little bit less) as the charge time. If it is, your capacitor is helthy and with the C value you just calculated.

Gunnar Englund
Half full - Half empty? I don't mind. It's what in it that counts.

RE: electrolytic capacitors shelf life

There was the famous "capacitor plague", but that was apparently confined to one capacitor manufacturer in Taiwan. Even those defective products lasted more than a year.

RE: electrolytic capacitors shelf life

Here is what I've been given for alum electrolytics in the past.

Quote (UCC)

Shelf life : 500 hours at 85C ambient temperature
Storage : within 3 years after production at 5C to 35C

RE: electrolytic capacitors shelf life

+85°C is pretty warm.

If we may assume doubling per 10°C, then it'd be at least four years at more reasonable temperatures.

RE: electrolytic capacitors shelf life

So trying to get back on the subject.

Has anyone actually "reconditioned? caps before? Does anyone know of a mathematical equation to do this properly without guesswork? Is there a chart somewhere online which lists voltages, correct current limiting for the cap size, and the time required to recondition them.

It would be nice to hear from someone who can say "yes I work in electronics repair and have reconditioned thousands of these. This is the procedure to do it........... and here is where you can find the info."

RE: electrolytic capacitors shelf life

I don't any post that are very far off-subject.

Here is an authoritative reference: http://bit.ly/1lbRKYY

First hit. Precise and authortative advice from a manufacturer.

RE: electrolytic capacitors shelf life

Typo: I don't *see any...

2nd hit is from another manufacturer. Hopefully you're happy with these authoritative results.

You probably shouldn't have thrown out all those old capacitors.

It's worth pointing out that reconditioning is essentially the same as installing and turning on the power; with increased risk in extreme cases if you don't limit the current. So if you ignore the problem then you'll also simply bypass the entire issue in most cases.

I hope this helps.

RE: electrolytic capacitors shelf life

Done all the Google searches before posting the question. Come up with nothing relevant. Yes just installing an old cap and turning on at full power will usually just work fine and they fix themselves. Electrolytic capacitors have when new usually a 20% tolerance. As sitting around too long they can not be tested accurately to verify that they are good or bad with a hand held meter. The reading will change if they fix themselves later on.

I try to do better quality work than putting something in crossing fingers and hope it works. I would like to get an accurate measurement before installing. If I am replacing one of these I wouldn't even use one more than 10% out of range. Some engineer somewhere decided on the rating and that is what I want to stick with or as close as possible.

On a note shelf life is not the same as service life. On a shelf they never see power and degrade. In service the same cap gets cycled on a regular basis and can last decades.

I may just have a bunch of these from the "capacitor plague" a few years ago or even "counterfeit" name brands. Over seas manufactures with very poor quality have been known to copy major brand labels. This is why I like to verify new parts are actually good parts.

RE: electrolytic capacitors shelf life

"Come up with nothing relevant."

What's wrong with the first two hits, from Illinois Capacitor and Panasonic? You need beyond what the manufacturers recommend?

RE: electrolytic capacitors shelf life

Again back to conflicting info. one source says it best to use 1/2 rated voltage the other says use full voltage rating. Other sources later on say never use full voltage which makes sense that if you push something straight to the rated breaking point it may break. Other sources are saying voltage does not mater. So like doing this with a D cell battery should work as good as a precision adjustable DC power supply for any cap. There is also conflicting times I have seen everything from 30 seconds to overnight.

RE: electrolytic capacitors shelf life

It's almost certainly a speed vs risk trade off. So the optimum depends on the circumstances and your judgment. In your case, take the most conservative advice.

RE: electrolytic capacitors shelf life

I just hate using my better judgment with nothing solid to back it up. From what I have researched and compiled would be to use a power source at 1/4 the cap rating with a 1K ohm resistor on the positive side for 10 min. then up the voltage to 50% the caps rating for 20 min.

RE: electrolytic capacitors shelf life

Read the posts IRstuff. That's At least 3 conflicting sources. Conflicting sources = Nothing solid

RE: electrolytic capacitors shelf life

So as a licensed A&P mechanic I am trained to have at least 3 reference that can verify that what I am doing is correct and confirmed by all the sources before ever touching an aircraft to a F.A.A inspector at any time. IRstuff as you list your profession as "aerospace" do you read and follow those procedures?

RE: electrolytic capacitors shelf life

They are not conflicting in the sense that if you pick the most conservative approach, it does not conflict with the most aggressive approach.

As for "aerospace," that includes defense, which is not subject to FAA regulation. Nevertheless, rather than waste time looking for "solid" sources, I can apply engineering analysis, test, and/or judgement to justify my decisions to my customers.

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RE: electrolytic capacitors shelf life

If I try and work out the torsional properties of a thin walled section there are at least three approaches documented, in textbooks, that I could use. Each will give different results.

Since the general aim of reconditioning capacitors has a rather indeterminate meaning, three reliable sources have come up with different, but roughly equivalent, recommendations.

You choose which one seems to apply, or a mixture to give the most conservative.


Greg Locock

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RE: electrolytic capacitors shelf life

Just buy new ones.. Hardly worth the time.
Some people just take "cheap" too far.

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