[R-390] Re: Capacitor Leakage Test

Thu, 29 Aug 2002 13:55:02 -0400

Rodney,

The leakage test to which I refer is the one mentioned by Dr. Jerry a couple 
of years ago.  The DVM or VTVM is set to the VOLTAGE mode and connected in 
series with high voltage power supply and capacitor under test.  The meter 
reading is interpreted as leakage current by dividing by the input 
resistance of the meter.  The meter's input resistance serves as a current 
limiting resistor.  The maximum voltage across the capacitor will be that of 
the power supply minus the meter reading.  The meter will read high for 
leaky, low for non-leaky.  If the cap has negligible leakage its voltage 
will be essentially equal to that of the power supply.

This test with a DVM on the 3 volt scale would be very sensitive, having a 
full scale current of 270 nanoamperes.

Drew
>
>Date: Wed, 28 Aug 2002 18:45:09 -0700 (PDT)
>From: Rodney Bunt <[email protected]>
>To: Drew Papanek <[email protected]>
>Cc: [email protected]
>Subject: [R-390] Depot Dawg / Capacitor leakage test
>
>The maximum voltage would be the "battery" inside the DVM say 9v. Only a 
>really bad 200v capacitor
>would leak at 9v !!!
>
>I have a Heath C3 Capacitance tester, and you can wind up the test volts to 
>450v and observe
>leakage on the magic eye tube as "noise" it is interesting to note how much 
>more noise there is as
>you wind up the volts closer to the operating voltage.
>
>Have a re-think about this as a testing aid. I got the Heath C3 tester on 
>ePay for $30, best
>investment I ever made, I have found capacitors that looked OK with the 
>DVM, but were leaky at
>high voltages.
>
>Rodney
>VK2KTZ
>

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