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Find out the farad rating of a capacitor?

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I pull a lot of scraps off of old electronics and use the parts from them. I use to never grab capacitors that were unmarked on the boards. I was wondering if any one knew a way to test for the capacitance(farad rating) of them with out having to buy a whole new multimeter?

Thank you,
 

dknguyen

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Most Helpful Member
Buy a capacitance meter or an LSR meter or build one.
 
Last edited:

crutschow

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Buy a capacitance meter or an LSR meter or build one.
Do you mean an LCR meter?

Some multimeters also measure capacitance.
 
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kchriste

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Usually the capacitors are marked somehow unless they are small SMDs. Maybe post a picture?
 

MikeMl

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Hero999

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I don't think the method on YouTube will give very accurate results because most DVMs are designed for 50/60Hz operation not 1kHz.
 

MrAl

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I pull a lot of scraps off of old electronics and use the parts from them. I use to never grab capacitors that were unmarked on the boards. I was wondering if any one knew a way to test for the capacitance(farad rating) of them with out having to buy a whole new multimeter?

Thank you,


Hi there,


The method you choose would be based on what test equipment
you already have in your possession. If you have a multimeter that
also measures capacitance then you would use that, but if you have a
scope and a frequency generator then you could use that.

If you dont have any test equipment then you'll have to look for
markings on the cap body itself, and if you dont find any then it will
be impossible to find out without any test equipment so you would
at least have to buy a multimeter with a cap tester on it too.
These are not expensive anymore so you could find one for cheap.

If you also want to test inductors then you would need an LCR meter
instead, and that would allow you to test inductors and capacitors.
You could also buy a scope and frequency generator or build a
frequency generator yourself, but the LCR meter would be easier.
With a scope and generator there are quite a few methods you
could use to measure both capacitance and inductance.

One thing to keep in mind is that electrolytic caps are polarized, so
you have to take care of the polarity of the applied voltage when
testing.
 
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Ghosty_Ghoul

New Member
An astable 555 plus frequency counter or 'scope is a good method of measuring an unknown capacitance.
 

Ghosty_Ghoul

New Member
I saw an MCU based LC meter somewhere on the Internet but I can't find it now. :(

Does anyone else know of it?
 

MikeMl

Well-Known Member
Most Helpful Member
I posted the link seven posts above yours in this very thread!
 

RCinFLA

Well-Known Member
Measuring the capacitance is simple. Finding the voltage rating is not, short of stressing them until they blow out.

Non-electrolytic used for low voltage circuits should be fine. I would be wary of using electrolytics without knowing their voltage rating.
 

tcmtech

Banned
Most Helpful Member
If you can reverse engineer the circuit it came out of its possible to get an educated guess at the voltage it worked at. As far as most modern digital multimeter's they work up into the multi KHz ranges now.
Even my cheap $3.99 one from harbor freight can read the voltage off my function generator and stay accurate up over 2 kHz.

Is the capacitor marked for a polarity?
 
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