Arduino for measuring Farads (vs micro/pico farads)

Question

I've been looking for a way to use an arduino to measure capacitance of a supercapacitor that is likely to have a 4F capacitance based on experiments of others.

Several people have experimented with arduino to measure capacitance in the neighborhood of picofarads and microfarads, experimentally demonstrating accuracy of different approaches. Example1.

"One meter would accurately measure values in the 1000 μF range, but it would fail in the nF and pF range. Another capacitance meter was accurate in the nF and pF ranges, but failed in the μF range."

Working through a supercapacitor experiment with Robert Murray-Smith, I see that the supercapacitor can hold 4 farads.

Has anyone experimented with accurately measuring larger capacitance with an Arduino and, if so, is there a documented approach that I can use as a starting point?

Any pointers are definitely appreciated.

Answer 1

To measure capacitance requires either measuring (a) impedance versus frequency, or (b) dV/dt versus current.

The problem with measuring pF range capacitors is that of stray capacitances swamping the device under test (DUT). High impedances for (a) or low currents and short times for (b) are difficult to realise. Similarly, but less so, for nF ranges.

μF to mF are generally easy to measure, reasonable impedances, and reasonable currents.

When you get to Farads, you may have problems with the software. Generally only method (b) is used for this range. Some people who make meters for lower ranges may simply not bother providing high enough charging currents, or long enough reading times, to measure this high. There's no fundamental problem, if you wait long enough, but the firmware of particular meters may not allow you to. The maximum capacitance measurement specification will reflect the charging current and the maximum measurement time they've allowed.