Discharging Elcaps

Hi there,

Why is it that after a capacitor bank discharge there is still charge left and the voltage is building up again? Who knows what this phenomenon is? This can be quite harmful for an circuit as this charge can cause short when the PCB is not stored in a secure place.

Best regards,

Enrico Migchels

0 albertosombri over 15 years ago

Hello Enrico,
where the ElCap is connected to?
Maybe it could depend of the electrical circuit connected to the capacitor.
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0 Former Member over 15 years ago in reply to albertosombri

It is common behaviour for electrolytic caps to show a small charge even after it has been shorted (and the short removed obviously). It is to do with the chemical recation in the electrolyte I believe, I'm sure a few minutes online search will explain more. The charge does not increase above some small level so it's generally not a problem.
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0 enrico.migchels over 15 years ago in reply to albertosombri

Hi Alberto,

Shorts are easily caused by careless touch up work, solder tin wire falling on the PCB, things like that. It is always best to place a bleeder resistor across an elcap but nowadays (in the green zone) products have to be as efficient as possible, so the bleeders are left out.

Best regards,

Enrico Migchels
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0 enrico.migchels over 15 years ago in reply to Former Member

Hi Rich,

Thank you for this reply. If you have additional information about the topic, it would be helpful. Not that it will prevent this from happening, but I like to know anyway.

Best regards,

Enrico Migchels
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0 WestfW over 15 years ago in reply to enrico.migchels

I believe the build-up of charge on a discharged capacitor (NOT just EL caps, by the way) is:
1) relatively common on high-voltage capacitors. (So large HV caps are frequently stored with a
shorting wire between the terminals.)
2) caused by longer-term polarization of molecules in the dielectric materials.
See "electret"; the electrical equivilent of a magent (has a permanent electric field.)
(actually, I thought this was relatively uncommon for EL caps, since they have fairly
high leakage currents. More common in film caps, or the most common example: the
capacitance inherent in a CRT tube...)
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