# Measuring the Internal Resistance of an Electrolytic Capacitor

I was wondering if its possible to measure internal resistance of a capacitor from a DC circuit using the below formula and method.

$\ V=V_0e^{\frac{-t}{\tau}}$

$\ lnV=-1/\tau\ *t + ln V_0$

Using a graph to determine the gradient can I then solve for $\tau\\$?

From there I was thinking of using total resistance R and subtracting the resistance of the resistors to find internal resistance.

$\ R= \frac{\tau}{C}$

$\ \frac{1}{R}= \frac{1}{R_{resistor}}+\frac{1}{R_{Internal}}$

Will this method give me valid results?

• Or you could charge the capacitor and measure $\tau$ as it discharges through it's internal resistance. – Chu Jul 14 '18 at 10:41
• Any measurement jig will involve some unavoidable inductance, complicating this simple RC case. – glen_geek Jul 14 '18 at 11:13
• Would the effect of inductance be significant on the results? – Wouter vw Jul 14 '18 at 11:35
• @Woutervw The lower your R is (and your R is already pretty low) the faster it discharges and the more L will affect the results. – DKNguyen Oct 24 '19 at 20:21