Rehydrating a dried up capacitor

[Refugee]

I have not seen anything before about this challenging procedure so I have decided to have a go myself.
It tested open circuit on the reformer.
Now it is time to find out what happens.

   

Right the first thing I did was to clean it up. There was quite a large plug of crystals in the vent hole.
The capacitor had been in a chassis with the terminals facing down so that it had plugged the hole and not collected any significant dust. I pushed it back into the can and added 4 cc of distilled water and allowed it to stand over night for it to soak in. I added some polyeuthrane varnish as I do on good capacitors with tired looking seals. I also plugged the hole with a bung from a computer ink kit.

   

I have applied power from my reformer and it is taking about 2.5ma at 50 volts. This figure has settled and if other caps of the same type are anything to go by it will now have to sit at this figure for something like 48 hours or so before any further assessment can be made.

Any guesses on on its chances?

[boiss]

Do you get a kick out of old caps?............................
I replace the innards with a modern one. I've got to do my Scope main cap. 4700uF.
It's about 4 inches long and about 1.5 in dia. The replacement is about 1.5 x 0.75.
What value is yours by the way?
Mike

[Refugee]

The one I am experimenting with is 32uf + 32uf at 450V.
Examples that have not leaked have taken about a week to reform. The voltage rises for a few hours and then drops to a value where it remains for several days before finally rising to 300V with a leakage of 100ua or less over the final 8 to 12 hours. I have eight of them all reformed and in there original amplifiers providing good service.
Yes that is right I do know what I am aiming for.
At the moment it id down to thermal cycling in order to get the distilled water all the way down into the roll of foil before I can assess the currant it is taking fully.

[boiss]

The one I am experimenting with is 32uf + 32uf at 450V.
Examples that have not leaked have taken about a week to reform. The voltage rises for a few hours and then drops to a value where it remains for several days before finally rising to 300V with a leakage of 100ua or less over the final 8 to 12 hours. I have eight of them all reformed and in there original amplifiers providing good service.
Yes that is right I do know what I am aiming for.
At the moment it id down to thermal cycling in order to get the distilled water all the way down into the roll of foil before I can assess the currant it is taking fully.

What is the failure rate of all the examples that you have tried, Did they all work out and are they all OK now?
Mike

[Refugee]

What I have is four push pull amplifiers a picture of one being my avatar. Each has two of these capacitors in it.
During the first round of restoration about two years ago the dried out capacitor was spotted and swapped out for one from the external power adapter.
The amplifiers are 110V only and the power adapters also contain a smaller power supply for a preamp containing one of these capacitors it also having a 110V only primary. I have two adapters.
Once reformed the ones in the amplifiers have proved to be fine and have not got hot or hummed since they were reformed. The three day process was used as there are big tag strips under the capacitors that would be destroyed should one blow.

[boiss]

Is this do-able with the one from my scope 4000uFd 40V ?
What is the process?
Mike

[Refugee]

Basically the seal in the rubber coated bung had perished leaving an open hole.
I just added distilled water and am giving it a try.
So far the currant it is taking from the reformer is following the same trend as the non leaked ones that reformed successfully so it is looking interesting.
It may well also work on the scope capacitor. Perhaps also give it a try.

[Nick]

Please remember that old capacitors often contain polychlorinated biphenyls which are known and powerful carcinogens as well as presenting other serious health risks, including liver damage...

http://en.wikipedia.org/wiki/Polychlorin...th_effects
http://www.epa.gov/wastes/hazard/tsd/pcbs/about.htm

Rather than risk them leaking again and exposing others to these potentially dangerous electrolytes, why not re-stuff the capacitors with modern, non-PCB, electrolytics which generally are of a smaller size and lower ESR. Jan Wuesten sells modern replicas which are PCB-free - http://www.die-wuestens.de/eindex.htm?/k1.htm - others sell equivalents as well...

[Refugee]

It is oil filled capacitors that contain the bad chemicals and they fail in a way that makes them impossible to repair.
The worst risk with oil filled capacitors is taking them to bits in order to re-stuff them.
I have seen the aftermath of an oil filled transformer that had blown up. It had a split in it like a pipe that had been frozen. There was oil all over the place.

[Nick]

It is oil filled capacitors that contain the bad chemicals and they fail in a way that makes them impossible to repair.

My bad - very true - Its was the oil-filled caps & transformers post 1940s that invariably contained PCBs.

The stuff in electrolytic caps seems reasonably innocuous... can be very corrosive though...