Barrie,
I cleaned the capacitor with Simple Green followed by the dishwasher per
your advice. Took the cap back my friend's shop today. The 1-2 microamps
of leakage at 1KV before the cleaning process was reduced to about one
tenth of a microamp afterward.
Then that I noticed some dark matter on the end of one of the
insulators, I'd call it carbon tracks but that may not be the right
term. I cleaned that area with a pencil eraser, removing the "carbon
tracks".
Tested again and found zero leakage current at 1KV.
The capacitance still tests higher than manufacturer specs . . . perhaps
my friend's Sencore LC-102 needs calibration :-\
Thanks everyone for the advice.
73,
Steve K8JQ
Barrie Smith wrote:
>
>
>> The LC-102 can also generate as much as a thousand volts for measurement
>> of leakage current. So I put 1000VDC (the capacitor is rated for 3500
>> volts) across the air variable and measured leakage current thru it. The
>> value of leakage current varied ranged between 1 and 2 microamps as I
>> turned the rotor. Leakage current seemed to be slowly increasing as
>> time passed. What is typical leakage current for this type of capacitor?
>> What is the leakage path? Can the leadage be reduced/eliminated? Or,
>> more to the point, should I be concerned with this level of leakage
>> current? As a comparison, I had three other air variables (including two
>> big transmitting air variables of the type used in Johnson KW
>> Matchboxes) that measured zero leakage under the same test conditions.
>>
>> Advice?
>
>
> As I mentioned in a previous post: Is the capacitor clean? Are any of
> the plates bent, or have nicks?
>
> Spray it with "Simple Green", let it set for a few minutes, and then run
> it through the dishwasher a couple of times. Let it dry completely and
> test it again.
>
> 1 to 2 microamps is way too much leakage for a 3500 volt cap.
>
> Leakage should be measures with the plates fully engaged.
>
> Leakage will increase considerably if there is dirt and grime on the
> plates or the end-caps.
>
> 73, Barrie, W7ALW
>
>
>
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