Rubycon MBZ leaks in storage!

[momaka]

Re: Rubycon MBZ leaks in storage!

Are you saying that overvolting caps with very low current will not harm the cap?

Well, I am not saying that overvolting caps is safe. But you can apply the maximum rated voltage on the cap without consequences, if you have a resistor in series with the cap to limit the current. Generally, that should be a few to a few hundred uA (microAmps), which for most electrolytic caps we use here, is close to their cap leakage current. With a 10 KOhm series resistor and 5V as the power supply, the maximum current that can flow through the cap will be 5V / 10 KOhm, or 0.5 mA (500 uA).

Also, electrolytic caps can usually withstand a "surge" voltage that is slightly higher than their rated voltage. For example, if you look in the United Chemicon KY datasheet, you will see that 6.3V caps can take up to 8V surge for short periods of time without damaging the caps.

In that case, there's no reason to reform the cap at a lower voltage, just at a low current, correct?

Not exactly.

Technically speaking, you may be able to get away with that, because once you go over the rated voltage on a cap, its internal leakage current greatly increases. And if you are limiting the current, the voltage across the cap will drop due to the increased leakage current. Of course, you'd have to be very careful about limiting the current. If you don't limit it enough, you can internally overheat the cap from the overvoltage and damage it.

So maybe I should set up some sort of decade resistance array hooked up to some kind of switching system on my jig.

Here is how I do it:

V1 is the power source - in my case a 20V laptop adapter for 16V and 20V caps and 9V wall-wart that outputs 14V unloaded for 10V and 6.3V caps.

The way I work it:
1. Remove the 10 KOhm series resistor (R1)
2. Adjust 1 KOhm pot (R2) to appropriate cap voltage (i.e. about 6V for 6.3V caps and 9.5V for 10V caps)
3. Re-insert back 10 KOhm resistor and leave the setup alone for some time

C1-C3 are the caps I wish to reform. You can have as many as you like in parallel (but less than 10 is a bit better to avoid large charging periods, especially when you go above 1000 uF caps). I usually build the setup on a breadboard and insert/remove parts and caps as needed.

I don't think I have any 12V adapters that can do more than 1A. But with a PC PSU, I can go all the way to the maximum of the 12V rail, or at least up to the 2A - 5A of current some of these caps handle.

With a 10 KOhm series resistor, you won't need anywhere near these currents. A few mA would be more than enough. So anything from a wall wart to a few 9V batteries in series will do the trick here.

[mockingbird]

Re: Rubycon MBZ leaks in storage!

Ok I was thinking that actively passing large amounts of current through the cap would be part of the reforming process. But that's too complicated for me to set up, and the way you are doing it is more than adequate.

Thank you very much for all the help.

[Topcat]

Re: Rubycon MBZ leaks in storage!

I've seen all the major brands occasionally do this. A lot depends on how it was stored.