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[AMPS] SSR's reforming electrolytic caps

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Subject: [AMPS] SSR's reforming electrolytic caps
From: (Tom Rauch)
Date: Wed, 5 Jul 2000 07:22:04 -0400
> One of the reasons I asked about users of SSR's in Amplifier 
> power supplies, was my interest in their off position leakage.  

They are like a switch. You'd have to turn it on just before zero 
crossing and depend on on the turn-on signal to vanish before zero 
is hit so it turns back off. 
> I often rebuild amplifier power supplies with older electrolytic 
> capacitor banks on board. I worry about these capacitors when 
> they sit idle for extended periods of time.  

If they are mixed with new ones or have deformed, they should 
have been replaced. 
> 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. 

Short of monitoring leakage resistance at or near full voltage, you 
wouldn't know if the capacitor is safe to use. 

I can't think of a safe and easy way to "reform" a series string of 
capacitors. If the caps are so far mismatched that equalizing 
resistors of the proper resistance don't work, then they are junk 

> I would hope this 1st ps mode would avoid "shocking" a long 
> time unused electrolytic cap and avoid a premature failure.  
With modern foil technology if leakage is excessive, the capacitor 
has already failed and will always be unreliable. I'm not sure what 
others in manufacturing have seen, but I've never seen an 
electrolytic recover from an age related failure. I've never seen a 
good electrolytic need "reforming" even when stored for years, or a 
bad one that was reliable in use (especially in a series string).


73, Tom W8JI

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