Capacitor testing

Test with multi-meter that it is not short circuited.

Test with capacitance meter that capacitance value is correct.

If this is an electrolytic capacitor I measure ESR.

With some electrolytics I charge them to nominal voltage with power supply and measure charging leakage current or the rate it self duscharges.

If it is a small mains voltage capacitor I might test that it can withstand the needed voltage rating with insulation resistance tester at 250, 500 or 1000 VDC test voltage.

1 Comment

  1. Tomi Engdahl says:

    Capacitors that regain charge over time after a short discharge are exhibiting dielectric absorption. Dielectric absorption is charge retained in the dielectric due to finite time required for electric dipoles to completely lose the alignment resulting from charging.

    Dielectric absorption is predominantly observed in film caps (small) and electrolytic caps (larger).

    Dielectric absorption can cause certain circuits, particularly certain reset circuits, to misbehave.

    In rare cases, when the initial stored charge, voltage, or both is large, dielectric absorption can cause dangerous conditions to “mysteriously” re-appear at a capacitors terminals after a period of time. In these cases it is recommended to keep a shorting strap on capacitors after an initial controlled discharge.

    Glass dielectric capacitors, like the second anode terminal on a CRT, can be subject to dielectric absorption. This occasionally causes unpleasant surprises during CRT service.


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