Cap reformation question

[Allison]

>
>Subject: RE: Cap reformation question
>   From: "Joe R." <rigdonj at cfl.rr.com>
>   Date: Tue, 06 Dec 2005 21:48:03 +0000
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>At 06:25 PM 12/6/05 -0600, you wrote:
>>I take a bench power supply and a resistor and bring the caps up that way-
>sometimes you have to disconnect a wire or two, but not always, and the
>resistor gives you a degree of safety a straight variac wouldn't.
>> 
>>
>
>   That's what I was thinking of doing. I keep a bunch of HP adjustable
>voltage/ adjustable current supplies around and they've come in handy for
>LOTs of different things. (I used one tonight to recharge and test some
>lead-acid batteries for my HP 5315 Freq meter then used to same supply to
>manually drive the VCO LO in a spectrum analyzer that I'm working on.)
>
>    Q: How high of a voltage do you use the reform the caps?  I'm wondering
>if it's necessary to apply full (or nearly full) rated voltage or if
>they're fully reformed at say 5 VDC. Has anybody done any testing in this
>area?
>
>   Joe

They need to be formed to at least the working voltage, it's better if
you can go closer to the rated voltage.

My trick has been a low current (120V pannel lamp) in series with whatever 
supply was needed/handy. The lamp (under 1W) will limit current flow
and they are cheap. 

Switch mode supplies are very risky at below rated voltage as the operating 
currents in many (older ones) gies up with decreasing voltage.  This are best
carefully, removing the caps and forming them out of circuit may be advised.


Allison