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# capacity test

#### emraude2008

Feb 10, 2011
9
hi i'm a student in electronic and i'm doing a poject but i have some diffucult, does any one here know how to do a capacity test , to if it's domaged or not

i really need the answer here is my @ [email protected]

Moderator
Sep 5, 2009
14,077

#### trobbins

Jun 15, 2010
83
emraude, does capacity = capacitance ?

Feb 10, 2011
9
i mean capacitor

#### shrtrnd

Jan 15, 2010
3,826
Are you asking for a method of determining the value of the capacitor? Or are you asking for methods to determine if a capacitor is good or not?

#### davenn

Moderator
Sep 5, 2009
14,077
i mean capacitor

ok well you can buy or build a capacitance meter as I suggested above
that will tell you its value
you can buy or build an ESR meter, that will tell you if its faulty

Dave

Feb 10, 2011
9
thanks dave

#### emraude2008

Feb 10, 2011
9
Are you asking for a method of determining the value of the capacitor? Or are you asking for methods to determine if a capacitor is good or not?
i'm looking for a solution that can determinate if the polarized capacitor is in the right direction in the circuit
the polarized capacitor is connected in parallel to a resistance

#### emraude2008

Feb 10, 2011
9
hi

emraude, does capacity = capacitance ?

i'm looking for a solution that can determinate if the polarized capacitor is in the right direction in the circuit
the polarized capacitor is connected in parallel to a resistance

#### trobbins

Jun 15, 2010
83
That will be tricky!!

Are you good at visual recognition software and webcam imaging ;-)

Sorry, but I can't think of an electrical technique that seems reasonable. An applied low voltage of different polarity may induce a different level of steady-state leakage current and not damage the capacitor (if voltage is not too far from zero), but your parallel resistance may swamp any suitable detection level of current.

Ciao, Tim

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
i'm looking for a solution that can determinate if the polarized capacitor is in the right direction in the circuit

OK, interesting question.

In general, a polarised capacitor should always have one end (the positive end) no more negative than the other end.

You might imagine that you could simply place a voltmeter across the capacitor, but that would simply measure the average voltage.

The best approach is to place oscilloscope probes across the capacitor (on DC) and have a look at exactly what the waveform looks like. You would want to look at if there are any excursions into reverse polarity and how they stand against the specifications for the capacitor.

Oddly enough, I was just reading a datasheet today that specified reverse voltage characteristics of a capacitor. In this particular case it recommended no more than 10% of the working voltage of the capacitor and gave leakage characteristics (somewhat higher than for the correct polarity). Frankly, it is not something that I have noticed (or indeed looked for) previously.

(And I can't even recall *WHY* I was looking at the specs of a capacitor?)

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