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[AMPS] SSR's reforming electrolytic caps

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Subject: [AMPS] SSR's reforming electrolytic caps
From: (Phil (VA3UX))
Date: Wed, 05 Jul 2000 10:04:28 -0400
At 08:15 PM 7/3/2000 -0700, you wrote:
>I'm in the process of working up a capacitor reforming mode 
>for power supplies using electrolytics.  The goal of this mode 
>would be to provide a very slow ramp up toward the normal HV, 
>allowing the capacitor to reform before the amplifier is step 
>started for operation. The amplifier would not be available for 
>operation during the reforming process. 
>I would hope this 1st ps mode would avoid "shocking" a long 
>time unused electrolytic cap and avoid a premature failure.  

I'm not sure you can really accomplish the reforming process in the short
time delay provided by an SSR.  My experience with reforming electrolytics
manually with a variable HV DC supply and milliameter/microameter shows
that "reforming" can take 30 to 60 minutes.  The ones that can't be
reformed (ie. the leakage current is excessive and remains that way) are
destined for failure whether you try to reform them or not.

When my desktop amps would sit idle for months at a time, I would run the
240V primary at 120V for an hour or two to "reform" the cap string before
returning the amp to service. I would do this with tubes removed.  I never
had a cap failure but then, I was reforming caps that weren't that old to
begin with and were known to be in good condition just a few months prior.
However if I were faced with some caps that had been sitting idle for
years, and in view of my experience with the manual reforming method, I
would highly recommend manually reforming each one separately to find the
duds in the string.


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