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My question is about whether there would be a problem with aluminum electrolytic capacitors that have been installed in an amplifier, then factory tested (so a current was run through them), then stored for four years.

I know that the shelf life of electrolytic capacitors is 2-3 years. But I have read some say that if they have been mounted on a circuit board and have received a charge during testing at the factory, they can then survive for much longer than their shelf life that with no problems.At the same time, others claim that the shelf life holds also for caps in circuits, when starved of electrical current.

So, the question is: does the shelf life of electrolytic capacitors also apply to capacitors in amplifiers that have in the past received an electrical charge, but have then been put into storage for a long time, at room temperature, in dry conditions? Or does having received a charge make the caps more resistant to chemical degradation in the absence of further charges.

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Shouldn't make any difference whether they are mounted or not.

The main factor in electrolytic capacitor lifetime is what temperature they are stored or used at and for how long at high temperature. Rule of thumb is that life halves for every 10°C rise.

So if they were stored in a cool place they'll have a long shelf life. If they were stored in an attic in Phoenix during the summer, less so.

Voltage was applied during testing at the factory (and before that to the raw etched foil), and it certainly leaked off within a short period after that.

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  • \$\begingroup\$ Thanks. So you are suggesting that cap shelf life under ideal conditions--which is usually specified by manufacturers as about 2-3 years--holds also for mounted caps that received a charge in the past, but have not been used for a while? \$\endgroup\$
    – Steve RD
    Sep 14 '18 at 19:53
  • \$\begingroup\$ Yes. Electrolytic caps will typically last for decades on the shelf. If it's already soldered you don't need to worry about solderability of the leads. \$\endgroup\$ Sep 14 '18 at 20:24
  • \$\begingroup\$ But then why do manufacturers typically specify a shelf life of just 2-3 years? \$\endgroup\$
    – Steve RD
    Sep 14 '18 at 20:46
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    \$\begingroup\$ To guarantee solderability of the leads and so there is lifetime left after they are installed in the product. End of life for electrolytic capacitors is typically when the electrolyte dries out. IC (Illinois Capacitors) states 15 years lifetime with derating. Remember there is an awful lot of 30+ year-old equipment out there with electrolytic capacitors that is working fine. \$\endgroup\$ Sep 14 '18 at 21:17
  • \$\begingroup\$ But I thought that to avoid the drying up of the capacitor, it has to be periodically subjected to current. That's the reason some people give for using a variac to gradually "reform" caps that have not received a current for a while. \$\endgroup\$
    – Steve RD
    Sep 14 '18 at 21:48

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