Looking for comments or improvement recommendations on this... i've been reforming some caps recently and came down to some simple guidelines which have been working well for me.
Maybe this topic exists, but couln't find one dedicated to this topic, just random mentions of reforming.
I became interested in the topic as i acquired quite a cache of old electrolytic i want to make use of.
I've read a few documents on reforming caps, and the methods very, the most common is simply putting a 1k resistor in series with the cap and hooking it ti a supply set to the working voltage of the cap for 30min.
reading deeper the methods all had a few things in common...there is a desire to keep the current limited in the beginning of the reform as to not overheat the capacitor and to ramp up the voltage as it reforms.. typical max current mentioned is 10ma but more often then not it was not mentioned. from all i can gather. though, not sure that rule applies universally. it seems like a good rule of thumb.
Also i've seen various methods mentioned for higher voltage capacitors., higher voltage like being above 50v. these methods all seem to be about the same things, keeping the current down and ramping up the voltage.
these methods include using higher series resistance and lowering the applied voltage and then stepping it up.
As i have been reforming, I've not seen where the internal resistance becomes better, or the measured capacity increases after reforming compered to the initial unreformed measurements. it does prevent them from failing when put into use though. I'm not saying it will not help internal series resistance or capacity, its just has not been my experience.
What i've been doing is simple and I've been sticking to 3 simple rules.
1. keep the reform current under 10ma using a series resistance.
2. work your way up to 100% working voltage. [ NOTE: if necessary lower the supply voltage initially but series resistance usually accomplishes this on its own. ]
3. once a stable leakage current is reached at 100% working voltage, leave powered for an additional 30 min.
so in example....this is how i may apply the rules for a given cap.
1. when I start with a resistance and voltage that will limit the short circuit current to a maximum of 10ma - personalty i've been sticking to under 5ma. and I work my way to a 1k series resistance and 100% of the working voltage. so for a 50v cap i start with a 10k series resistance. and once the current drops down to like .5ma i'll change to a 1k resistor.
1a. the series resistance lets to voltage on the cap slowly rise as the current drops.
1b. i have a current limited supply, but do not use the current limit feature as the way to limit the current to the cap. i use in the resistance. as using the current limit alone with no resistance would put a high voltage on the cap immediately, which would break my rule 2
1c if a capacitor is 50V or under i start with the working voltage applied to the series resistance. for over 50V if not then i'll increase the voltage in 3 stages 50% 75% and 100% not that i count use the resistance alone, its just easier to deal with in my setup and also increasing the voltage is mentioned as a methodology for high voltage electrolytics in a few documents i''ve read.
2. once i'm at 1k resistance, and 100% working voltage, i'll wait until the once the leakage current becomes stable, at that point i'll leave it connected for an additional 30 min.
oh and... i never let this process run unattended.
any comments are appreciated. help me fine tune the rules