Electronics > Beginners
Test capacitors without an ESR meter?
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cbmeeks:
Is there a way to get a good estimate on the life of a capacitor without an ESR meter?

Especially something a little more accurate than "it's good" or "it's bad".  Like something that would estimate a cap being within 10% of specs or 80% of specs, etc.

Thanks!
setq:
A good thing to remember is that a low ESR doesn't imply that the capacitor is any good. I've had a couple of them read fine on an ESR meter and then blow up in my face. So the policy developed of ignoring the ESR meter and just replacing them in anything that comes through the door regardless of condition if it's more than about 5 years old.

Yes quite a few end up being binned even if good but I've been on the hot end of a Sprague Atom before and don't recommend arguing with them or taking a risk.
cbmeeks:
Ah, good points.

I restore vintage computers.  Some of them are pushing 40 years old...but I admit that I don't always do a full recap on them.  Maybe I should replace them more often.
Kleinstein:
It is possible to get an ESR test with an square wave generator a resistor (could be 50 Ohms output impedance) and a scope. The generator could be as simple as a NE555 or 74HC14 based one. Sometimes even the adjustment signal of the scope is good (strong) enough.
helius:
Additionally, dielectric leakage of capacitors is another common failure mode that is separate from high-ESR. It can be tested with only DC instruments, while testing ESR requires an AC setup.
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