Hhm, this measurement can become a bit tricky, because the ESR of such a cap is so small. More, as the inductance of cap might be much bigger it could cover the ESR.

Equivalent series circuit at 100kHz of such a cap is:

C=3300µF, Lc is about 15...30nH, Rc<9mOhm (hopefully)

The impedances at 100kHz are then: ZC = 0.5mOhm, ZL = 10...20mOhm and R <9mOhm (hopefully).

So, if you take your signal generator and feed a 100kHz sine into a series circuit of suited resistance (R) and cap, in order to drive a "constant" current into it, then you might notice, that the signal drop across cap is very very low: Assume you can drive a R=600Ohm load by a 10V sine, resulting in a current of 10V / 600Ohm = 16.7mA, then the voltage drop across a 20mOhm impedance will be about 330µV!

So, I would recommend to amplify the voltage drop across cap by a suited amplifier.

For this measurement the following equivalent circuit is valid:



Take note, that C does not appear, it's just so small, that its impedance can be neglected.

Rc can then be gained by a simple amplitude and phase measurement according to the following mathematics:




Kai