If you come across aluminum electrolytic capacitors that have been sitting idle in a cabinet somewhere for a very long time, chances are those capacitors will have degraded pretty badly.
There was a classic movie "The Seven Year Itch" that starred Marilyn Monroe back in 1955. The story line was that almost every American male starts losing interest in monogamy after seven years of marriage, which leads to a series of fantasies that the audience gets to share.
Speaking of fantasies, I was once involved in a proposal effort for a large, automated test facility. It was not the U.S. Navy VAST system for which I actually designed some stuff, but for a different agency that rejected the proposal to which I refer. Yes, the proposal effort was a failure.
Still, there was one requirement to which I took exception that may merit a little thought. It was to be required that the equipment for this system be capable of being idled for seven years—just left there in storage and then, with not so much as a thought, be immediately powered up and brought into service. I said, "No."
The equipment would have had power supplies amidst all the other stuff and those power supplies would need to have aluminum electrolytic capacitors. With thousands of microfarads being required, there was no way that tantalum capacitors (dry or wet), or ceramic capacitors, or film capacitors could possibly provide enough microfarads. Aluminum electrolytic capacitors would be absolutely necessary and such components could not be guaranteed to still be serviceable after seven years of disuse.
I read somewhere that two years of disuse is pretty much the maximum idle time for modern day electrolytic capacitors, but in my personal opinion, I would lean toward even shorter time frames for those parts being purchased, installed, and energized.
If you ever happen to come across some geriatric aluminum electrolytic capacitors that have been sitting idle in a cabinet somewhere for a very long time, chances are those capacitors will have degraded pretty badly. However, you might be able to achieve capacitor resurrection along the lines of "aluminum electrolytic reclamation."
The movie implies the possibility of marriage breakdown in seven years. Technology implies aluminum electrolytic capacitor breakdown in less than seven years. Caveat engineer.
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
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