Electronics Forum / Basics / December 2007

If it's a really old piece of kit , and has electro caps in it, just
replace the lot.
They guys who built it probably didn't know what ESR was in those
days, it's only become obvious with modern smps IC's, needing miniohms
of ESR

martin

Don't bother with that one, get what everyone else in the industry
has:
http://members.ozemail.com.au/~bobpar/esrmeter.htm

Bob Parker hangs out on the aus.electronics group, so you can ask
questions there.

There is also this one, which even Bob himself has heard good reports
about:
http://www.peakelec.co.uk/acatalog/jz_esr60.html

Dave.

I built this one http://www.flippers.com/esrktmtr.html - - really good - -
have enjoyed using it for about 4 months, now. Check out my comment on the
flippers website about 3/4 of the way down the page.

Chuck Olson W6PKP

My opinion, It does not come close to actually giving you a true
ESR reading.
 All the design is doing is relying on high valued capacitors assumed
to still have life and hoping to display the effective series resistance
in them by assuming the Xc to be at a very low value with the 50khz
referenced used.
  In practice, that isn't a real ESR meter.

When I worked at Semco, the preferred method used on the automation line
for ESR testing was to apply a 1 us pulse to the cap via a low value
R from a stable pulse source.
  Both the pulse source and net result reference from the cap under
going a test were being monitored via a high speed comparator.
  When the pulse source reached it's max peak it would force another
 comparator to briefly update a sample and hold circuit for a generate
voltage offset difference;

 Theory of operation was that most caps when discharged (shunt shorted)
would exhibit virtual 0 (Xc)with a fast raise pulse, and the net results
of the resistance formed by construction and leads would then not allow
for an absolute short to common which would give you a reference to work
with that could then be translated into Ohms.
  Part of the components were mounted in the probe assembly arm to
reduce induction in the equation.

  Using this method, it did not matter if the cap was a small or large
value type. it simply only did the acquisition of readings on a single
 positive transition.

  This method was check against other equipment in the lab that was
designed for Q testing of small and medium value and found to be very
accurate.

I built and use it.  It is adequate for good/bad/questionable diagnosis.  
It is also simple to assemble, I built mine from "junk" parts.  I don't
think I could beat it for the price...