Don't need $100...
Electronic circuit schematic for capacitance meter, free on the Internet.
If you have a scope with a calibrator, you can check ESR:
Determine calibrator's output voltage and series resistance:
My Tek 561B calibrator has an output of .4V with 50 ohms series resistance... Since a reasonable capacitor's ESR will be below .2 ohms, we can assume the calibrator will see a dead short (this is fine, the calibrator is meant to be shorted to calibrate current probes).
So .4V/50=8mA
So now, let's connect a capacitor across the calibrator.
Look at the calibrator waveform on the scope when shorted with the cap - it will look like a triangle wave, except it will have big jumps where the trace changes direction. Measure the voltage of these jumps.
On a cap I measured a few hours ago, the jump measured 1.2mV.
So do the math with Ohm's Law:
1.2mV/8mA=.15 ohms
This was a 600uF 200V cap from a TV set from the 70's... (it was a good TV BTW, built like a tank. All that time, and the thing that killed it was NOT a bad cap...)
You can also calculate the capacitance by looking at the slope of the triangle wave, but I haven't looked up the math for that yet.
- keantoken
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