Testing a capacitor in curcuit w/ analog meter?

[smoketest]

Testing Capacitor w/analog meter in circuit

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Hi.. would process below be any diffrent with capacitors in circuit on board

1) Discharge the capacitor by shortening its leads. That is - use a wire and connect the leads of the capacitor together. This will discharge it.

2) put your multimeter in the high ranges 10K-1M

3)CONNECT MULTIMETER TO CAPACITOR LEADS(OBSERVE THE POLARITY IF ELECTROLYTIC). AT SOON AS THE LEADS MAKE CONTACT, THE METER WILL SWING NEAR ZERO. IT WILL THEN MOVE SLOWLY TOWARD INFINITY. FINALLY THE METER WOULD COME TO BE INFINITE OHMS BECAUSE THE CAPACITOR IS BEING CHARGED BY THE BATTERY OF THE MULTIMETER.

4) IF THE CAPACITOR IS BAD, IT WILL GO TO ZERO OHMS AND REMAIN THERE. THIS IS CALLED A SHORTENED CAPACITOR

5) IN THE CASE OF AN OPEN CAPACITOR THERE WILL BE NO OHMMETER INDICATION.

6)SOME CAPACITORS HAVE A LOW DIELECTRIC LEAKAGE. YOU WILL KNOW THIS IF THE OHMMETER COMES TO REST AT A POINT LOWER THAN INFINITE. TEST A KNOWN GOOD CAPACITOR OF THE SAME TYPE TO BE SURE

1000uf 16v capacitor tests after discharge on x10 scale analog meter

measurement upon reading goes to about 5 ohms and stops
when reverseing leads goes to about 60 ohms and stops on some and discharges on others
my analog meter is powered by 2 aa batt 3V is that enough voltage to
load capacitor? or is still being in a curcuit giving me strange readings
I am getting readings like this on Caps that appear fine.
Thanks for any help or advice........ Dan
   

[Hero999]

Simply short circuiting a capacitor is a bad idea because the current will be very high so could weld the wire to its leads. It's much better practise to discharge it using a resistor to limit the current to under 10A.

A word of warning: obviously be careful around large capacitors charged to high voltages (above 60V) and beware that dielectric absorption can cause a discharged capacitor to recharge slightly. I'd recommend keeping the capacitor terminals shorted for a couple of minutes before conducting the test.

The method you've described only works for large value capacitors (<100uF or so). It won't work with a 1uF capacitor.

The voltage rating of the meter makes no difference.