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Capacitor Testing 
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To test a capacitor quickly, use an ohmmeter.  On your ohmmeter select Rx1 or Rx10 for a large value of capacitor (>1uF) and Rx100 or above for small values (<1uF).  Discharge the capacitor first by shorting the capacitors leads together.  Don't touch both leads with your fingers until the capacitor has been discharged or you may get shocked.  Put the positive probe of your ohmmeter to the positive lead of the capacitor, do the same with the negative probe. Your meter pointer should swing to zero resistance then swing to infinity.  Discharge the capacitor again and repeat the test this time touching the negative probe to the positive lead.  The meters pointer should swing to zero resistance then swing close to infinity.  If you get these results the capacitor is probably OK.  If a capacitor is an open-circuit (bad) you will get infinity resistance on both readings.  If it is shorted (ad) you will get zero or near zero reading and it will never swing to infinity on either reading.  A good capacitor that can store a charge with less leakage will show an infinity resistance reading, which means no current flow, after it is fully charged.

This test is satisfactory for some but not all capacitor testing.  It will tell you very little to nothing if the capacitors value is very small.  And, it tells you little to nothing about its capacitive value or voltage handling capability.

Now you may ask, how do I measure an unknown capacitors capacitance?  Well, below are a few web links that will show you how to build simple capacitor measuring instruments.  You could always buy a capacitor tester but that wouldn't be as much fun would it.  Often you can find used capacitor testers on eBay but you have to be careful not to get a lemon.  Try building one first.  You will learn more that way.

The following WWW links will take you directly to the various web site pages.  Your browser URL address line will tell you the origin of the site.

LINKS

1. Circuit of linear-scale capacitance meter
        site: Amateur-Circuitry
2. Circuit diagram of the simple direct-reading capacitance meter
        site: Amateur-Circuitry
3. Frequency and Capacitance meter
        site: Circuits Arсhive- University of Washington
4. CAPACITANCE BRIDGE
        site: Electronics for You


 

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