## 12252Re: Capacitor testing

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• Apr 12, 2009
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--- In midatlanticretro@yahoogroups.com, "Bill Dromgoole" <drummy@...> wrote:
> I don't see how your method is simpler or more effective than Mike's method.
> I probably just don't understand your method.
>
> If I understand you correctly you are putting a 30 Kohm resistor in series with
> the Capacitor being rejuvenated and measureing the voltage across the resistor.
> When the leakage current is equal to one milliampere the meter would read 30
> volts and at 0.5 ma it would read 15 volts, etc.
> The voltage accross the capacitor is unknown unless you have a seperate meter to
> see the output voltage from the power supply.
> You would then need to subtract the two voltages to get the capacitor voltage
> unless you have a third meter to measure capacitor voltage.
> The purpose of this exercise to to make a bad cap good again, if possible.
>
> As you can see, I don't fully understand your method.
>

<< If I understand you correctly you are putting a 30 Kohm resistor in series with > the Capacitor being rejuvenated and measureing the voltage across the resistor.>>
** That is correct. That configuration makes the approach simpler because of less equipment needed. You only need a variable PSU, voltmeter, and 3-5watt 30k resistor.

<< When the leakage current is equal to one milliampere the meter would read 30 volts and at 0.5 ma it would read 15 volts, etc.>>
** Correct.

<< The voltage accross the capacitor is unknown unless you have a seperate meter to see the output voltage from the power supply.>>
** Most variable PSU's have an output Volt/Ammeter built in. So you can either infer V across cap by subtracting the voltage drop across resistor from your PSU's voltage readout... OR you can just move one lead of your VDrop meter over to the cap's opposite terminal.. since you've already got one lead on it where the resistor is.

<< unless you have a third meter to measure capacitor voltage. The purpose of this exercise to to make a bad cap good again, if possible.>>
** Yeah, the purpose is to reform the oxide layer on the foil roll within the cap... assuming there's enough electolyte left in there to where it's not dried out, and assuming there's not shorts or other problems.

To recap, my method is simpler just in equipment setup, and also potentially gives you a longer cap life by the 10% push (the point of which is to give you more of an oxide layer.. well within the design limits of the caps).

jS
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