ESR Meter

[Bob Nickels]

I agree wholeheartedly with Mike and others about the value of ESR testing of
electrolytic capacitors.  Once you try it, you'll be a believer too!

Not to detract from the excellent designs that are recommended - but it's so easy
to rig up your own ESR measurement circuit, there's no reason not to give it a try
yet tonight!

All you need is any old oscilloscope and some kind of signal generator that cover
the "range of interest".  By that I mean a frequency where the cap under test will
have a low reactance it is "good" (i.e. low ESR).   Connect the output of the
signal generator, the input of the o'scope and a pair of test leads all in
parallel - that's it!   With the probes disconnected you will see the output of
the generator.  Now if you touch the probes to a good capacitor, the generator
output will be shunted by the capacitive reactance and the scope display will
become very low in amplitude.   Check a few old caps and you'll quickly see the
difference - many will only be able to reduce the signal by half, or even less.
The amplitude of the signal displayed by the scope is proportional to ESR.

A neat trick:  limit the amplitude of the test signal to < 0.7 volts and you can
test capacitors in-circuit without biasing transistors on.! The service tech who
developed this method claims he reduce his repair time on consumer electronics by
over 50% and it's a good way to use some old test equipment.  I just keep Ch 2 of
my dual-trace scope hooked up and simply switch to that channel when I want to
measure ESD.   Good luck with this simple method of visualizing ESR.

73, Bob W9RAN

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