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Old Feb 4th 2013, 01:07 AM   #1
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Measuring capacitance

Hi I`m new here and a 70 years old "garage tinkerer" in the UK. is there anybody out there who can show some insight into a means of attaining the actual capacitance of an unusual capacitor that I have already built, and which I wish to step charge, using the known details ie "power in over time say 12.98vdc voltage for 10 minutes, and retained voltage say 2.47vdc over "total discharge time taken" to zero? say 2 hours 31 minutes 47.4 seconds?

I do have a Chinese capacitance meter which isn`t too bright but I have or can have fairly accurate voltage insertion times and values ( with a PWM controlled voltage in and digital tester)
Any help would be much appreciated. I wish to wind a pair of chokes to create resonance in the capacitor. creating a resonant circuit.
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Old Mar 6th 2013, 12:29 PM   #2
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Capacitance can be measured by RC time constant
Charge the unknown capacitor with known battery through known series resistor. Connect the voltmeter across the capacitor. Note the time consumption for voltage to build from 0 volts to 63% of the battery voltage across the capacitor.

T = RC it can rewritten in C = T/R
T is the time in sec, taken to charge capacitor from 0 to 63% of battery voltage
R is known resistance in ohms and
By above calculation it will give C capacitance in farads
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Old Mar 6th 2013, 01:26 PM   #3
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Measuring a capacitance

Thanks Andwer. I will see how I get on with that! Regards Rob
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