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Old 5th August 2003, 11:14 PM   #1
Rarkov is offline Rarkov  England
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Exclamation 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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Old 5th August 2003, 11:15 PM   #2
tiroth is offline tiroth  United States
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This is normal. Look for info on dielectric absorbtion.
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Old 5th August 2003, 11:51 PM   #3
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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,
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Frank
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Old 6th August 2003, 01:00 AM   #4
andy_c is offline andy_c  United States
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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
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Old 6th August 2003, 07:06 AM   #5
Rarkov is offline Rarkov  England
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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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