Self-discharge electrolytic capacitors

[capator]

Hello.

I have understood that an electrolytic capacitor has a self healing effect when disconnected in such a way that, when it is disconnected after being charged in DC, its self-discharge resistance is much bigger that the resistance when was connected across the DC voltage.

Am I right? How much bigger?

I would like to know in depth this phenomena, could you bring me some hints about it ?

Thank you very much.

[MDOC]

Re: Self-discharge electrolytic capacitors

No, because of the phrase you mentioned: "when it was connected across the DC voltage." In that configuration, there is no discharge because DC is continuously applied to it. If the phrase is modified this way: "when it was connected across a bleed resister to ground," you'd be right. But, without connecting the cap's leads to themselves or to a circuit, there is little or no discharge.

[cheapie]

Re: Self-discharge electrolytic capacitors

His post makes almost no sense... I think he's trying to talk about reforming.

[budm]

Re: Self-discharge electrolytic capacitors

Not sure if he is asking about self-discharge, the charged cap will self-discharge (when it is disconnected from the source) the due to internal leakage resistance.

[MDOC]

Re: Self-discharge electrolytic capacitors

yes, there is some discharge, how much I don't know but depends on the size and capacitance. Big caps can hold a charge for a long time.

[budm]

Re: Self-discharge electrolytic capacitors

http://www.analog.com/library/analog...ersary/21.html

[ben7]

Re: Self-discharge electrolytic capacitors

Capacitors always self-discharge (except when at a low voltage - they can have a battery effect!). Even when there is power being applied across the capacitor, it is discharging, but the power source keeps refilling the stored power reservoir (the capacitor/capacitance). This discharge is called leakage current.

The datasheets for the capacitors will specify the leakage current. A capacitor discharging fast, with no external power source applied, means either the leakage current is high, and/or the capacitance has dropped. Don't mistake this when evaluating a small value capacitor!

[MDOC]

Re: Self-discharge electrolytic capacitors

OK - but I meant that a cap removed from a circuit will hold a charge - there is no discharge.

[budm]

Re: Self-discharge electrolytic capacitors

It will still have self dis-charge due to it leakage resistance, Rp. Very important in high Z circuits.
Read the link on post 6.

[MDOC]

Re: Self-discharge electrolytic capacitors

It will still have self dis-charge due to it leakage resistance, Rp. Very important in high Z circuits.
Read the link on post 6.

No. This leakage (Rp) is through a resistor in parallel with a cap. A cap, especially a large electrolytic one, will hold a charge if cap is removed from a circuit. The charge will dissipate eventually over time, but too slowly enough that it will still hold a charge.

[budm]

Re: Self-discharge electrolytic capacitors

Charge up the cap and see for yourself if it will hold the same voltage, that Rp is in parallel with the cap since no cap has perfect insulation between the two plates, it has very high resistance which will eventually drain the cap.
The Rp represent the real world cap circuit, not the circuit resistor.
If you design high Z circuit, you will know how important of the Rp will be. The leakage current can be in uA or mA range, no cap has perfect insulation between the two plates.
http://www.newton.dep.anl.gov/askasc...0/phy00900.htm

https://cdn.badcaps-static.com/pdfs/...bcd99f6e92.pdf

[MDOC]

Re: Self-discharge electrolytic capacitors

Depends on the cap design. Had a cap pop on me years ago in class after several minutes.

[ben7]

Re: Self-discharge electrolytic capacitors

Depends on the cap design. Had a cap pop on me years ago in class after several minutes.

What do you mean?

[Ahakim]

Re: Self-discharge electrolytic capacitors

It seems that what you mean is not what we understand... Would you please rephrase your inquiry about cap discharge. You will get the right answer/explanation...

[MDOC]

Re: Self-discharge electrolytic capacitors

What do you mean?

I meant that soon after charging up a large cap, the cap was shorted, and there was a loud bang. A period of time, I don't remember how long.

[MDOC]

Re: Self-discharge electrolytic capacitors

I believe it was much longer than several minutes... hours. Certainly less than 24 hours.

[ben7]

Re: Self-discharge electrolytic capacitors

Yeah they can hold a charge for days!