electrolytic capacitors shelf life
electrolytic capacitors shelf life
(OP)
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?
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
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
http://www.Hi-TecDesigns.com
RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
"Love your user name" LOL
RE: electrolytic capacitors shelf life
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
RE: electrolytic capacitors shelf life
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.
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
RE: electrolytic capacitors shelf life
https://www.youtube.com/watch?v=HuALonM_1X4
RE: electrolytic capacitors shelf life
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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?
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
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: electrolytic capacitors shelf life
TTFN

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RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
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
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
Here is an authoritative reference: http://bit.ly/1lbRKYY
First hit. Precise and authortative advice from a manufacturer.
RE: electrolytic capacitors shelf life
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
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
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
RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
You've got at least 3 sources from what you've just said, so you have lots of solid backing. As an engineer, it's up to you to adjudicate situations like this.
TTFN

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RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
RE: electrolytic capacitors shelf life
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.
TTFN

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RE: electrolytic capacitors shelf life
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.
Cheers
Greg Locock
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RE: electrolytic capacitors shelf life
Some people just take "cheap" too far.