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Using "new" old electrolytic caps in new circuits - Yay or nay?

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Gyro:

--- Quote ---I saw BigCliveDotCom "activate" a fake electrolytic capacitor by adding electrolyte to it (it was a dry capacitor, like the kind you see in scam fake "oem" caps sold by shady bootleg vendors). In theory, would adding new electrolyte to a cap after it has dried out "reactivate" it in a sense?
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In theory, yes. The practical problems are that the electrolytes used are weird (usually secret*) cocktails which vary from manufacturer to manufacturer (and probably type to type too, eg long life vs Low ESR or temperature rating). The other one is how to introduce the correct amount of electrolyte without creating a new leakage path - I suppose something like a very fine hypodermic followed by some sort of sealing compound might work.

So yes, replacing what has evaporated off would theoretically do it, if the electrolyte has leaked past the seal though, you'd face serious issues with corrosion eating your PCB tracks.


A little OT, but at one time, people used to try the same sort of thing with dried-out NiCd cells, it mostly worked... Again the problems were sealing and existing leaks but at least in that case, there was no fancy recipe to worry about, just deionized water.


P.S. * A few years back, there was a huge issue with low ESR capacitors on PC motherboards etc. It turns out that it was mainly due to one manufacturer attempting to 'duplicate' another manufacturer's formula. Google 'Capacitor Plague for more details.

tggzzz:

--- Quote from: WyverntekGameRepairs on December 22, 2019, 10:25:23 pm ---Knowing that age affects the performance and reliability of these capacitors, how good of an idea was it for me to use old electrolytics (even if they are Rubys) in a medium-voltage circuit?

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Often answering a question is much easier than working out which is the right question to ask.

I suggest a useful question would be "what is the cost if one of the capacitors fails?".

WyverntekGameRepairs:
Thanks everyone, all of this information is highly useful! :)
So in conclusion, it is indeed okay to use an old or NOS capacitor in new personal projects as long as the ratings are still accurate and the capacitor is showing no signs of leakage or damage. There is an easy test to determine if an old cap is still useable or not:

--- Quote from: MagicSmoker on December 22, 2019, 11:30:25 pm ---Loss of electrolyte over time due to imperfect sealing around the terminals is a major cause of "death by senility" in aluminum electrolytic capacitors. This failure mechanism causes ESR to rise - sometimes dramatically - and there is no curing it. So, a good first pass test of any NOS (New Old Stock) capacitor is to measure its ESR. And how do you know if the ESR is too high or still ok? Well, that very much depends on the capacitor, but a general purpose elko will have a dissipation factor, DF, which is the ratio of ESR to Xc, of around 10-20% (0.1-0.2). An elko is usually considered EOL (end of life) when DF has doubled.

For example, a 100uF capacitor will have a capacitive reactance, Xc, at 1kHz (a common frequency used to test ESR) of 1.59 Ohms, so a good capacitor should have an ESR of between 0.159 and 0.318 Ohms (ie - 10% to 20% of Xc), while an ESR of >0.6 Ohms would be suspect.

The other age-related failure mechanism is a loss of the dielectric layer over time which causes the DC leakage current to increase, perhaps to the point of causing the capacitor to overheat and possibly even explode. However, this failure mechanism can be reversed by merely applying a slowly increasing voltage to the capacitor over time which re-forms the dielectric layer. How slowly? No prizes if you guessed the answer is, "it depends...," but I've seen recommendations as wide as going from 0V to rated voltage at the rate of 1 minute per month of storage to 1 hour per year of storage; in my experience it doesn't really matter, just keep an eye on the actual current flowing through the capacitor after each increase in voltage and wait until it has dropped below a few hundred microamps before increasing the voltage again in steps/amounts no more than 1% of the capacitor's rated voltage.

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It is also possible to "reactivate" an electrolytic cap by adding electrolytic solution, but it is definitely not recommended for use in projects, and is more for experimentation with capacitors and capacitor engineering - not general hobbyist cap-revival methods.
After doing some investigation into the posts above, it seems that capacitors that experience use, even if occasional, have a longer life than unused caps of the same age that have not been maintained for shelf life. This depends on the quality and materials of the capacitor.
And finally, it is best to just use common sense when attempting to use NOS caps in a project, of course. If it looks or measures suspicious, then it *is* suspicious.

strawberry:
'used' capacitors are still fine (spot with the eagles eye) to use them, most cases 90% of juice is still there.
Old good quality capacitor is better than brand New dirt cheap one
Electrolytic capacitors placed near hot heat source is no point testing
Larger electrolytic capacitors are more durable than smaller or low profile
In last 20 y capacitors are made out of water based electrolyte with lower ESR values than older capacitors before, downside is if chemistry is wrong it will generate H and eventually went

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