[Boatanchors] Electrolytic Reforming Time

[Robert Nickels]

On 12/30/2011 11:50 PM, Phil wrote:
> So, it doesn't pay to take any chances with those 'lytics.
I agree with all that's been said but would just add that this business 
of "bringing it up slowly on a variac" should be relegated to the urban 
legends file.  It's better than just applying full AC power, but is 
still guesswork.   The only way to properly reform an electrolytic - 
regardless of age - is to limit (and measure) the amount of current 
being applied to attempt to "reform" the anode oxide layer that was 
"formed" at the factory when the cap was manufactured.

A good description of how the aluminum electrolytic capacitor works can 
be found here:
http://www.elna-america.com/tech_al_principles.php

And here's a good reference for how to reform capacitors properly as 
well as some alternatives:
http://www.nmr.mgh.harvard.edu/~reese/electrolytics/

I prefer to measure and limit the current to about 5 ma while the oxide 
layer is reforming; trying to do the job by simply cranking up a variac 
every so often might work some of the time, but is like tuning your rig 
while blindfolded.

I generally just replace electroyltics that are  cheap and readily 
available and attempt to reform those that aren't.  I think most 
"reformers" find the process can restore 80-90% of old caps when done 
right, without fear of explosions or failure.

73, Bob W9RAN