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life extension, Electrolytic capacitors
AndyH-ha
post Sep 23 2012, 22:08
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Electrolytic capacitors undergo chemical deterioration when there is no charge across them for a long enough period. They can develope other problems too, but they generally continue to function longer if they are in use rather than completely idle. If one has some "vintage" equipment, such as a cassette deck or VHS player that gets called upon for action only infrequently, and upon random occasions, it might be advisable to power it up now and again to keep the electrolytics in better condition.

First question: are there circumstances for which this is not true? Would the shelf life of some equipment be extended by only turning it on when it is really needed?

Assume the equipment cannot be left somewhere where it could be turned on for a little while anytime one happens to think of it. It needs to be stored out of the way, so it must be unpacked and set up, at least minimally, when something is to be done with it. Is there any frequency, based on actual collected data and/or knowledge of the chemistry involved, that is likely to do the job without being more often than really necessary?

In general, for how long should the device be left on to optimally "heal" the capacitors? I have no idea if the process is likely to be finished in seconds or only after several days, although I would guess it probably depends to some extent on how far the deterioration has progressed.

It may be the case, at least for older capacitors that might be past their prime, that bringing up the voltage across them gradually is more likely to lead to success. Is this generally true?

I'm thinking this gradual voltage increase could most easily be accomplished with an SCR type variable light dimmer such as is sold for home use; a mains power cord on its input side and a mains plug for the equipment on its output side. Is there any reason related to the equipment we are trying to preserve that such a setup might not be a good idea?

If it can work, how should it be worked? Is it best to bring up the voltage over a number of seconds or a number of hours?

Are there other considerations I haven't thought about?
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sthayashi
post Sep 26 2012, 06:18
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I had a pretty lengthy answer written up, but in trying to confirm much of the things I had written, I came across this site, which strikes me as being more accurate with regards to caps than what I had written. They touch on what you're talking about, but from the perspective the engineer.

The short answer can be boiled down to: this is likely a terrible idea as electrolytic caps are just part of the whole system, and if they're shoddy, trying to do something different that the design engineer hadn't considered may negatively affect other parts.

Your last suggestion is a bad idea as an SCR dimmer will apply a sharper voltage transition to the device under question. Look up the waveform for an SCR dimmer.

Your best bet is to just fire it up periodically. Maybe once a year, since most capacitor manufacturers state that the shelf life of their caps is 2-3 years. And while it's probably overkill, leaving it on for 30 minutes seems to be best time to wait (again most manufacturers give this number for reforming the electrolyte AFTER the shelf life has expired).
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AndyH-ha
post Sep 27 2012, 18:18
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Thanks for the information!
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