Cursitor Doom wrote:


I have the Atlas/Peak ESR meter which I have yet to get to grips with. I
figured it was worth acquiring since I have a ton of stuff that uses
electrolytics awaiting repair.

I still haven't worked out, however, why it is that this meter can
perform ESR measurments in circuit whereas for capacitance one has to
lift a lead. There's probably some obvious answer to this conundrum I'm
overlooking.

** The ESR test involves using a 100kHz signal and computing the impedance of the cap at that frequency. This equates closely with the true ESR for almost any electro in the range specified. Ideally, the frequency would be variable and the lowest impedance found would then be the exact ESR reading.

Luckily, this kind of test only places a small voltage ( millivolts) on the cap and impedance readings are normally under 5 ohms, so can be done in circuit with little or no effect from what might be in parallel with the cap.

Trick is, you have to have a good idea what the ESR of the particular cap was when new so you can see if it has risen significantly. Comparison with new caps of the same size, value, voltage and grade (low ESR or normal)is the best method. Reference to published tables is a very poor method.

Testing the capacitance of an *electro* is another matter and usually involves using a fixed DC current and measuring the rate of voltage rise on the cap. Resistors and semiconductor junctions in parallel with the electro will cause current to be drawn away an so you get false readings.



..... Phil