How to check a CAPACITOR

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beenthere

Joined Apr 20, 2004
15,819
If it's not electrolytic and you can't meter it, then you might as well taste it.

Defective electolytics usually show signs, like blown-out vent plugs, or having grown noticablly taller than the label.

Why do you need to be able to check caps without test equipment?
 

Dave_

Joined Mar 22, 2007
28
Wow, I've never really thought about that until now. I don't think it's possible to use a multimeter. The first way that comes to my mind is put it into a RC network, and calculate how long after charging fully it should discharge to 37% of its final value.
 
You can use your multimeter as an ohmmeter to test the capacitor.

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
 

thingmaker3

Joined May 16, 2005
5,084
Vincin's method will work with sufficiently large capacitor values. (Especially if one uses an analog meter.) Tiny capacitors can only be checked with a capacitance meter, or by using them in an AC circuit and checking for variation from calculated voltage drop.
 

Tube Tech

Joined Jan 11, 2007
46
Adding to what Vincin said: Reverse the leads and look for a major kick in the needle. If the cap charged from the DC voltage induced by the meter, the cap will discharge when the leads are reversed, causing a twitch in the needle.
 

alim

Joined Dec 27, 2005
113
To effectively test acapacitor one should use capacitance meter -one that reads in uF nF pF, an ESR meter is very useful for checking electrolytics in circuit, they are cases where the uF was good on acapacitance meter but cap had high ESR as shown on an ESR one. The point is one meter may not adequately serve all your needs.
 
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