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Old 06-06-2019, 01:39 PM
 
Location: SC
8,774 posts, read 5,606,850 times
Reputation: 12766

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Capacitors go bad, that is not in question.

The question is... Do Capacitors go bad "because they have been in use?"

In other words:

If two identical electrical parts of the same design are both made 30 years ago, and these parts have multiple capacitors within:
  1. Part #1 is sold and put into service immediately and is continually in use for the 30 years until the capacitors fail - leaking.
  2. Part #2 is not sold, but instead, sits on the shelf as a spare part.

Is part #2 then a viable and good choice to replace part#1, with just as good a chance of working for the next thirty years - because it had never been used before?

Or is it more likely that part#2's capacitors will soon fail too because even though the part was not in use before, it's capacitors are just as old as those that were in part #1?
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Old 06-06-2019, 01:56 PM
 
Location: Aurora Denveralis
8,082 posts, read 2,816,523 times
Reputation: 12044
I assume you're talking about electrolytics. Most other types (solid) have a virtually infinite storage lifespan.

But not really. If they've been kept under good conditions (cool, mostly), years of storage shouldn't affect them much. Maybe their rated value will change, but most are 10% or more precision and just used in bulk-capacity mode. Maybe their lifespan will be a little shorter, but not significantly.

If they're cracked, leaking or suspiciously light (meaning the electroyte slowly evaporated through a leak), they're probably bad. But in good condition - years don't matter too much for these.

It's relatively easy to test big caps. Charge them to near rated voltage (or something a little safer, with 50V and higher), and check the charge after a few hours and a day. It should not leak away with no drain path. If they're bad, the charge will be gone in minutes to an hour.
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Old 06-06-2019, 01:59 PM
 
Location: Somewhere in northern Alabama
17,739 posts, read 53,869,694 times
Reputation: 30005
It depends. Capacitors don't fail from only one cause, nor are all failures catastrophic. In general, a properly stored capacitor that has been properly manufactured and sealed will outlast one within a circuit, because the number of modes of failure are reduced. That said, caps do deteriorate over time, with few exceptions - such as the old variable plate capacitors used through the 1950s. OTOH, I've had caps that re-formed and healed themselves in circuits where the radio or amplifier hadn't been powered on in years and initially appeared to be dead.

This may help:
https://www.illinoiscapacitor.com/pd...ectrolytic.pdf
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Old 06-06-2019, 02:07 PM
 
Location: Aurora Denveralis
8,082 posts, read 2,816,523 times
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Quote:
Originally Posted by harry chickpea View Post
OTOH, I've had caps that re-formed and healed themselves in circuits where the radio or amplifier hadn't been powered on in years and initially appeared to be dead.
You must be talking about old wax-dipped ones, where the heat of use would reflow the coating and seal any cracks.
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Old 06-06-2019, 03:00 PM
 
Location: SC
8,774 posts, read 5,606,850 times
Reputation: 12766
Thanks.
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