[Collins] Another 30L-1 good idea .....how to test the capacitors

[Dr. Gerald N. Johnson, electrical engineer]

As said the test depends on the survival of the bleeder resistor. It
also fails to measure the series resistance of the filter capacitors
which contribute most of the ripple in failure mode. It reads additional
leakage current as reduced capacitance which isn't really a true result.

For more direct ease of capacitor value computation you can note the
unloaded voltage, then time the meter down to the 37% point. That's one
RC time constant, so the C value is the time in seconds divided by R.
I've used that with an ohmmeter (reading the linear voltage scale
instead of the ohmmeter scale on an analog Simpson 160 that I carry in
my traveling tool box) to read a motor starting capacitor to within 20%
while doing the timing by counting "thousand one, thousand two..." I
computed 10 mfd, the capacitance bridge some other engineer brought to
the scene said 8 mfd like the label said. So despite the fact that the
motor capacitor case had expanded from motor heat to a wooden barrel
shape, it wasn't the cause of the motor failure. I made the reading by
checking the capacitor "resistance" on a high range starting with the
capacitor discharged. For R I used the center scale reading of the
ohmmeter scale.

73, Jerry, K0CQ, Technical Advisor to the CRA.
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.