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Testing a capacitor in curcuit w/analog meter?

Discussion in 'General Electronics Discussion' started by Dankou, Apr 22, 2012.

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  1. Dankou

    Dankou

    2
    0
    Apr 22, 2012
    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
    is setting on multimeter Right for cap size?
    I am getting readings like this on Caps that appear fine.
    Thanks for any help or advice
    Dankou

    .
     
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    The problem with testing in circuit is that you have to make sure that there arent any resistors in parallel with the caps

    This will give you somewhere below what the resistor reads, and you have other circuitry

    Capacitors I generally tell people to read with a digital meter, and if its close to what it is supposed to be then leave it, if its way off take it out and read it again

    Capacitors block all DC, which is the signal that you get from the meter (resistance test usually puts out 2.5 volts, give or take) so theoretically it should read infinite, but infinite does not mean the cap is good, nor does a low reading mean that the reading is bad

    Ideally I would say get a digital multimeter with cap test on it
     
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