Capacitor Wizard (ESR Tester) Meter Movement

If you really wanted...

The idea is pretty simple. A discharged capped will have an ESR with effectively no initial voltage and therefor will act as a voltage divider with a known resistance. By measuring the voltage ratio you know the ratio of resistances.

For an ideal cap the measured voltage would be 0. For a reading of 1/2 the voltage would mean that the ESR has the same value of the known resistance.

You can play around with this idea to get more precise measurements. It is not a great method because as soon as a voltage is applied the capacitor charges and skews the result. Using an AC wave and for large caps it is not too bad.

Another method that is similar is to load the cap in a delta or wye configuration or use a wheatstone bridge.

BTW, the whole idea is to find a way to distinguish

--R---C

and --C--

(or when R = 0 in the first case)

For R to matter current must flow "through" the cap so there is a voltage drop through R. Hence rapidly charing and discharging the cap(much faster than it's time constant) will allow you to effectively ignore C and then it becomes simply a resistance measuring problem.

Alternatively you can charge up the cap and note the deviation between the ideal curve(R = 0) and non-ideal(which changes the time constant). Since when the cap is completely charged no current flows and no voltage drop on R while initially there is a voltage drop across R. This method doesn't work in circuit since.

You spent $45 on a meter movement?

Send it back. You can get them without the extra paint for $10.

Regards. Bob Monsen

Cool. There are times when only a real meter will do.

John

Nice link! Ed