[Boatanchors] cap leakage test

[J. Forster]

Norman J McSweyn wrote:

> Stupid question #3125:
> What exactly does a capacitor leakage test determine?

A real capacitor can be modeled as a parallel combination of an R and C, and that parallel pair in series with another R.

The series R is roughly the ESR
The parallel R is roughly the leakage resistance

> And does this number have any relation to the "D" value of a capacitor?

In a good capacitor the series R is small, the parallel R  is large.  D & Q are related to those R's.

> Next stupid question:
> Will these new meters that do esr

ESR see above.

> and dcr check caps "thouroughly" enough to be of (from a test point of view) value in a circuit at 200 to 500 volts?

Depends on the tester voltage. Leakage in electrolytics can vary strongly with voltage (and time). I would test a C at slightly above the operating voltage or at it's rated voltage.

> I might as well admit I can be obtuse sometimes. I can understand how a meter can determine cap values.

There are two different techniques..  charge / discharge and a bridge

> I can understand how an inductor can be tested for value.

Same two techniques with voltage and current swapped and bridge.

In either case, the readings can be misleading if the parasitic elements (the R's) are significant...  i.e. poor quality L's and C's.

-John

> I can understand an ohmmeter.
> As a side note, a bit of time has been spent trying to understand how lcr meters do their thing. R is easy. It's the L and the C that make things intresting.
> Time to quit banging my head for this evening.
> Norm
>
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