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Old 01-15-2019, 08:00 PM   #1
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Default Increased uf in old capacitors?

I've noticed when recapping amplifiers and speaker crossovers through the years that the old caps are sometimes increased in capacitance? I recapped a speaker manufactured in 1973/4 just recently, all of the Elcap brand caps were increased in value significantly and some even doubled in capacitance? The only thing I can think of to cause this is that some of the electrolyte has dried out between the layers bringing them closer together thereby increasing the capacitance, or that a chemical reaction has taken place in the electrolyte? Or it's the Aliens! Any other ideas on why this increase happens?
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Old 01-15-2019, 08:09 PM   #2
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Default Re: Increased uf in old capacitors?

it is a sign of internal electrical leakage.
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Old 01-15-2019, 08:28 PM   #3
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Default Re: Increased uf in old capacitors?

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it is a sign of internal electrical leakage.
How does that work? Could you give some details, please?
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Old 01-15-2019, 08:34 PM   #4
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Default Re: Increased uf in old capacitors?

breakdown in the insulating layer.
meter the resistance - they should be totally open circuit.
if they become leaky they take longer to charge - so the meter thinks they have a higher capacity.

your using the wrong tool for the job!
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Old 01-15-2019, 08:51 PM   #5
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Default Re: Increased uf in old capacitors?

Those Elcaps are bipolar, of the two caps inside one shorted section would then read 2x the rated value.
Some cap meters mistake leakage currents (longer ramp charging) as increased capacitance.
Older electrolytics were generous and actually at +20% for tolerance. Newer parts are typically -20% I find.
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Old 01-15-2019, 08:52 PM   #6
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Default Re: Increased uf in old capacitors?

Quote:
Originally Posted by stj View Post
breakdown in the insulating layer.
meter the resistance - they should be totally open circuit.
if they become leaky they take longer to charge - so the meter thinks they have a higher capacity.

your using the wrong tool for the job!
The resistance on those two caps shown in the photos is not open circuit! Both cycle from 1 million ohms to 500K ohms?
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Old 01-15-2019, 11:19 PM   #7
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Default Re: Increased uf in old capacitors?

exactly, they have internal leakage between the poles/plates
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