"reforming" electrolytic capacitors?

[Daravon]

I've heard that electrolytic capacitors that sit for a while (years) will lose their oxide layer and should be 'reformed' by gently bringing them up to voltage and limiting current until the oxide reforms and their leakage current is acceptable. Just plug them in, and their leakage current after sitting will be so great that they could burst.

Well I have an old power pack for a xenon photographic flash, and I initially plugged it in with a 100W bulb in series with the power cord. The bulb lights up and then goes dim when the caps charge...but not completely out. It stays barely glowing, showing that the caps have significant leakage current (unless there are other current draws in the power pack). When I fire the flash, the bulb lights completely up and then dims down within 10-15s, but never really goes out.

I'm not sure if the thing to do is to leave it plugged in for a long time with the lightbulb in series, leave it plugged directly into the wall for a 'long time', or to cycle the flash a lot. What's the proper way to bring electrolytic capacitors back up to full capacity?

 

[zipplet]

The best way in my experience is to apply a voltage to the capacitor that is quite low (for example, 5V) for a while. Then if the cap has a higher rating, e.g. 20V bring the voltage a bit higher and repeat.

This worked for a couple of big caps in an old power supply.

The problem is you would have to remove the capacitors. You would probably get away with leaving the unit powered on for a few hours instead.

 

[digitor]

Is it a Metz? The procedure in the manual for these (and a few other flashguns) is to power them up, then fire a few flashes every three months or so.

The reason the bulb keeps glowing would be the normal operating current I would think, this won't drop to zero once the caps are charged.

Cheers

 

[Daravon]

It's a Novatron 440hdx.

The best way in my experience is to apply a voltage to the capacitor that is quite low (for example, 5V) for a while. Then if the cap has a higher rating, e.g. 20V bring the voltage a bit higher and repeat.

This worked for a couple of big caps in an old power supply.

The trouble with that is that the caps are, I'm guessing, probably 500V or something, and I don't have a DC power supply that goes that high. That's why I'm trying the cord method. I will probably just plug it in every so often or start actually using it.