Longevity of PSU Electrolytic Capacitors - diyAudio
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Old 31st October 2008, 10:44 AM   #1
cotdt is offline cotdt  United States
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Default Longevity of PSU Electrolytic Capacitors

How long do brand name electrolytic capacitors continue to perform? I read in the datasheets that the "shelf life" of an electrolytic is about 10 years, but I have some old amps with ELNA Audio capacitors that's been going for 3 decades, and still measure great. Its properties have not changed in all this time. Meanwhile, the computer grade capacitors typically don't even last past 1 year.

Doesn't shelf life only apply to capacitors that are not being used? Hmm but it doesn't seem to be true. I took out some NOS Blackgates that has been in storage for decades and they seem to work just fine. Is there any concensus on how long good quality electrolytics last? What are the brands that make durable capacitors?

Anyone know the mechanism that causes electrolytics to break down over time? Though I'm a chemist and physicist I've never really looked into this.
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Old 31st October 2008, 12:16 PM   #2
mflorin is offline mflorin  Romania
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Old 31st October 2008, 04:11 PM   #3
AMV8 is offline AMV8  United Kingdom
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Hi codtd

It is a subject that I would also like to understand better.

I am an engineer and not a chemist so please excuse the loose chemical terminology. However I have dealt with audio for over 40 years so I can give you some habds on experience.

I have collected some very high quality electrolytic ps caps. I have some very old ones that are not used. Others used for different lenghts of time.

As everyone experiences, most, if not all, electrolytics do go off with use. I suspect they all go off with long use eventually; certainly all of mine have.

Unused caps seem to last a long time, especially if kept in airtight packing. I normally keep them in individual plastic pockets when being stored.

How do they go off? Chemically I am not sure. However they seem to dry out.

I would be interested to hear what you think is happening as they "go off".

Don
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Old 1st November 2008, 02:29 PM   #4
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The first thing to degrade if electrolytic caps are stored and unpolarized is that the oxide layer starts to thin, increasing leakage current and decreasing voltage rating. The shelf life is (at least for RIFA caps) the time it takes before leakage current at working voltage goes out of specification.

The caps are not destroyed though, you can reform them by applying charging current limited to some mA and let it take a while before working voltage is reached. This builds up the oxide layer again restoring it's original voltage rating. You can continue to apply current in this way increasing the voltage capability of the capacitor even more, but capacitance will reduce more the higher voltage it is formed to.
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Old 1st November 2008, 02:43 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by megajocke
restoring it's original voltage rating. You can continue to apply current in this way increasing the voltage capability of the capacitor even more, but capacitance will reduce more the higher voltage it is formed to.
I asked this question a while back and no one came forward with an opinion.

"Can an electrolytic be reformed to work at a voltage higher than it's rated maximum?"

How far can this be pushed?
What are the downsides to this, if it's possible?
Where can we find references to this technique?
What do manufacturers have to say on the matter?
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Old 3rd November 2008, 09:31 AM   #6
AMV8 is offline AMV8  United Kingdom
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megajocke

"you can reform them by applying charging current limited to some mA and let it take a while before working voltage is reached. "

Are you able to expand upon that statement if possible giving some information on the charging current/voltage and time.

Any information would be appreciated.

Don
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Old 3rd November 2008, 10:51 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
reforming is discussed in this Forum and also Google for other references.
Many manufacturers list reforming as part of the test preparation/procedure to ensure consistent results in their component specifications.

I have used 100k and 75Vdc to reform 63Vdc caps back to 63Vdc.

If I had left them longer, i.e. exceeding 24hrs, would they have become 65Vdc or 68Vdc capability?
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