I'm doing an experiment to investigate the internal resistance of an electrolytic capacitor in a DC circuit. Doing this I am measuring the discharge voltage against time, finding tau and from there finding the total resistance in the circuit, which then I subtract the known resistance from to find the internal resistance. I was wondering if there is a relationship that I can find between capacitance and internal resistance, from my research all I have found is information regarding AC current.

Any help would be much appreciated.

  • \$\begingroup\$ Why use a DC method while everyone else uses AC? I was wondering if there is a relationship that I can find between capacitance and internal resistance Not clear what you mean, do you expect the capacitance to change? Or do you mean a more general relation between value and ESR related to the value of the capacitor? \$\endgroup\$ – Bimpelrekkie Jul 12 '18 at 7:56
  • \$\begingroup\$ I would use DC because of the equipment available to me. What I meant was if there is a relationship between the capacitance of the capacitor and the internal resistance of the capacitor. From the answer below I gather there isn't. \$\endgroup\$ – Wouter vw Jul 12 '18 at 8:44
  • \$\begingroup\$ It's not possible to measure ESR by DC. You need some changing voltage. \$\endgroup\$ – Chupacabras Jul 12 '18 at 9:32
  • \$\begingroup\$ Internal resistance of a capacitor is a design decision made by the manufacturer. Thinking of a capacitor as two or more metal plates separated by thin dielectrics, the construction (especially the thickness of the plates) and the plate sizes will determine the resistance. Note that some capacitors are specifically designed as "low ESR" caps. \$\endgroup\$ – WhatRoughBeast Jul 12 '18 at 12:11

There is no direct relationship between capacitance and internal resistance. Indirectly, the thinner the metal the higher the resistance and the higher capacitance per unit mass/volume of the capacitor.

Additionally discharge rate will also be limited by inductance - whether we have multiple plates stacked in parallel or two plates and the whole thing rolled up


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