Self Charging Capacitors?!

Rarkov · 6th August 2003, 12:14 AM

Hi,
After a recent trade I have gotten some 230000uF, 25V caps. When they arrived, I checked their voltages present. They were all around 1.5V to 2.0V. I discharged them with a 1R 5W resistor, and they discharged immediatly. However, whilst I sat there, I noticed them GAINING charge! They were going at about 5mV per second. I thought they may have been "stealing" charge from the multimeter but I took the multimeter off at 20mV and when I checked again, it was at 32mV!

Is this normal & what is it?!

Thanks,
Gaz

tiroth · 6th August 2003, 12:15 AM

This is normal. Look for info on dielectric absorbtion.

fdegrove · 6th August 2003, 12:51 AM

Hi,

Quote:

Is this normal & what is it?!

Memory...caps are pretty smart buggers...not that that helps us audio folk in any way.

See why using those as coupling caps isn't such a great idea?

Cheers,

andy_c · 6th August 2003, 02:00 AM

Hi,

It's a classic case of dielectric absorption. Here's an article that discusses it:

http://www.national.com/rap/Applicat...570,28,00.html

Rarkov · 6th August 2003, 08:06 AM

Thanks very much...Very informative. I've never heard of it before. I suppose it doesn't really matter because the caps will have bleeder resistors over them.

Thanks again,
Gaz

6th August 2003, 12:14 AM	#1
Rarkov diyAudio Member Join Date: Aug 2002 Location: North East, UK	Self Charging Capacitors?! Hi, After a recent trade I have gotten some 230000uF, 25V caps. When they arrived, I checked their voltages present. They were all around 1.5V to 2.0V. I discharged them with a 1R 5W resistor, and they discharged immediatly. However, whilst I sat there, I noticed them GAINING charge! They were going at about 5mV per second. I thought they may have been "stealing" charge from the multimeter but I took the multimeter off at 20mV and when I checked again, it was at 32mV! Is this normal & what is it?! Thanks, Gaz

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6th August 2003, 12:15 AM	#2
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	This is normal. Look for info on dielectric absorbtion.

6th August 2003, 02:00 AM	#4
andy_c Banned Join Date: Apr 2003	Hi, It's a classic case of dielectric absorption. Here's an article that discusses it: http://www.national.com/rap/Applicat...570,28,00.html

6th August 2003, 08:06 AM	#5
Rarkov diyAudio Member Join Date: Aug 2002 Location: North East, UK	Thanks very much...Very informative. I've never heard of it before. I suppose it doesn't really matter because the caps will have bleeder resistors over them. Thanks again, Gaz

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