A capacitor that just wants to accumulate voltage

[Sadface]

HI Guys,

I was desoldering some electrolytic capacitors from an old AV for salvage today when I encountered one that just wanted to accumulate a voltage.
I was working away when I suddently had a spark when I shorted the -ve rail and ground.
5000uF/71V and the thing just wanted to build it up.
After the spark is had -20vdc on it.

I used a 2k resistor to de-energise the thing. Desoldered it and measured it again.
With it connected to my DMM and nothing else, I watched accumulate voltage at something like 100mV per second.

This doesnt strike me as normal behaviour.
Does anybody know what is going on here?

I am aware things like CRTs can accumulate voltages by themselves but I've never seen it in a capacitor before.

 

[Michael Bean]

That's caused by something called Dielectric Absorption, or Capacitor Soakage.
This will explain it better than I can:
Dielectric absorption

Mike

 

[Sadface]

Thank you.

My next question:

Is it worth keeping the capacitor?

 

[MarcelvdG]

Yes, if you have an application for it. All capacitors have some dielectric absorption and electrolytic capacitors have more of it than most other capacitors.

 

[nigelwright7557]

Its possessed !
Electrickery.

 

[bucks bunny]

Certainly haunted!

 

[rayma]

Just leave it overnight (or longer) with a short across the terminals.

 

[cracked case]

Use it to make a perpetual motion machine.