Digital Multimeter All
Can I use internal resistance to detect failing capacitors?
I haven't seen this mentioned much so i'm curious if it's a valid approach. I have multiple identical electrolytic capacitors all with internal resistors. When measuring resistance (ohms)with a digital multimeter (AC & DC), most of the discharged capacitors start at 0 and increase to the internal resistance value then hold there. I have one cap that only charges to 2/3 internal resistance, one that keeps charging past the int res value (towards infinity), and one that instantly reads the int res value. Is it safe to assume that all three of these caps are failing? I do understand that this method may not detect all failing caps, I just want to know if I can use it for an initial culling. Thanks!
It is a bad idea to ask a very general question and assume that an answer applies to every capacitor ever made!
It is impossible to measure the internal resistance of a capacitor with a DC ohm meter. You are misinterpreting the results. You have to use an AC ohm meter ("ESR" meter) to check the internal resistance.
I assume that the "internal resistors" are bleeder resistors designed to discharge the capacitor for safety reasons.
If that's the case:
>most of the discharged capacitors start at 0 and increase to the internal resistance value then hold there
That's what you expect.
>I have one cap that only charges to 2/3 internal resistance,
There is no reason for the resistor to be of close tolerance, so it might be the resistor is just lower than the others, or their may be a lot of leakage in the capacitor. But if the capacitor hasn't been used in a while the leakage might be temporary. See: reforming capacitors
>one that keeps charging past the int res value (towards infinity)
The internal resistor isn't connected; this may be a safety issue. The ohm meter is just slowly charging the capacitor.
>one that instantly reads the int res value.
The capacitor is internally disconnected from the leads. = bad
>I just want to know if I can use it for an initial culling.
Obviously you can spot whether the resistor or capacitor is internally disconnected.
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