Testing Capacitor w/analog meter in circuit

Discussion in 'General Electronics Chat' started by Dankou, Apr 21, 2012.

  1. Dankou

    Thread Starter New Member

    Apr 21, 2012
    2
    0
    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 Dankou
     
    Last edited: Apr 21, 2012
  2. #12

    Expert

    Nov 30, 2010
    16,294
    6,804
    You will almost never get a final reading of infinite ohms doing "in circuit" tests.
    That's why it isn't working.
    The rest of your theory is basically sound.
     
  3. jtrent

    New Member

    Mar 11, 2012
    26
    4
    The process you describe is essentially correct for simple testing of capacitors out of the circuit. However there are two things I would change.

    1. When testing an electrolytic capacitor you do not need to observe polarity. You will be reversing the leads anyway, so polarity is of no concern.
    2. The scale you set the analog meter on will be determined by the value of the capacitor. Use higher scales for smaller capacitors, use lower scales for larger capacitors. The voltage and internal resistance of your analog meter also affect your results, which may require different meter settings.
    As far as testing a capacitor in a circuit, there is no good way to do it using a meter because it will be measuring all of the rest of the circuit that the capacitor is connected to. If you suspect a capacitor is at fault, the best in circuit test would be to bridge a capacitor of like or similar value across it in the circuit and use an oscilloscope to see the results. In the case of audio circuits you just need to listen for a change in the output.
     
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