how stable is the parallel resistance of an electrolytic? - diyAudio
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Old 17th August 2014, 05:23 PM   #1
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Default how stable is the parallel resistance of an electrolytic?

Capacitors leaks current.

So a real world capacitor is like an ideal capacitor with a parallel resistor (of course, series resistor and inductor, too.).

The parallel resistor value seems to be high in some capacitor (10000 MOhm) and low in some electrolytics (less than one MOhm).

Anyway, it that parallel resistor value stable with time (many years) and temperature as long as the capacitor is used well within the temperature and voltage spec?
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Old 17th August 2014, 05:38 PM   #2
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Often, the leakage current is given by 0.03*C*V or 3uA whichever is greater.

So the parrallel resistor will be 1/(0.03*C).

For example, an electrolytic capacitor with the spec of 470uF, 25VDC, will have a parallel resistor larger than 0.071 MOhm?

Is this the right calculation?

Anyway my question is whether that resistance value is constant over time, temperature variation (but far below 85 degrees C), etc.
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Old 17th August 2014, 08:46 PM   #3
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One should presume infinity resistance or the capacitor is leaky.
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Old 17th August 2014, 08:52 PM   #4
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Electrolytic Caps are best applied where their variable and/or poorly speced characteristics don't cause problems

leakage current which can be indicative of parallel R is highly variable with temp, age - high leakage is often is often speced as one of "end of life" numbers
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Old 17th August 2014, 08:52 PM   #5
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Quote:
Originally Posted by ringing View Post
The parallel resistor value seems to be high in some capacitor (10000 MOhm) and low in some electrolytics (less than one MOhm).
Measured by what equipment ?
Do you own an LCR bridge meter ?
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Old 17th August 2014, 09:00 PM   #6
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No, that resistance varies all over the place, with age, temperature, on-time and anything else you can think of. It's an interesting exercise to set up a power supply and measure leakage current with a series resistor and DVM. Do it. Vary everything and see what happens. You'll learn a lot.

BTW, I don't think you have this problem, but don't confuse the simple parallel loss model with the DC leakage resistance term.
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Old 17th August 2014, 09:53 PM   #7
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Quote:
Originally Posted by Kiriakos View Post
Measured by what equipment ?
Do you own an LCR bridge meter ?
I read the specs avaliable at Mousesr.
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Old 17th August 2014, 09:57 PM   #8
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Those specs are generic, nothing that you can use in sound applications.
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Old 17th August 2014, 09:59 PM   #9
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If parallel resistance is acceptable, you just need to know what it is?
You could put a known stable resistor (perhaps 100K) in parallel.
That should swamp the unknown possibly non-linear component.
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Old 17th August 2014, 11:24 PM   #10
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Quote:
Originally Posted by kenpeter View Post
If parallel resistance is acceptable, you just need to know what it is?
You could put a known stable resistor (perhaps 100K) in parallel.
That should swamp the unknown possibly non-linear component.
If the parallel resistance changes (with age, temperature, etc.) +/- 60% from 1000 MOhm, it would not matter much for me. If it changes +/- 60% from 0.2 MOhm, it matters.
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