How to measure the capacitance of Supercapacitors/EDLCs

Supercapacitors are also known as ultracapacitors and Electric Double Layer Capacitors (EDLC). These types of capacitors have higher capacitance values than other capacitor types available today. Some EDLC capacitance values can reach up to 4000F in a single standard case size, such as Nichicon’s JJD0E408MSEGBN. It can be frustrating trying to measure the actual capacitance of these parts; how can you measure the capacitance of a part measured in thousands of farads with normal testing equipment?

Supercapacitors are different from other types of capacitors when measuring their capacitance. They have very large capacitance values that standard equipment cannot be used to directly measure. The common way to test these parts’ values is using this ‘charging and discharging’ method.

  1. Charge supercapacitor for 30 minutes at rated voltage
  2. Discharge supercapacitor through a constant current load
  3. Measure voltage drop between V1 and V2
  4. The discharging time between V1 and V2, T(sec) is measured and capacitance is calculated from the following formula.
    C = I * T(sec) / (V1 - V2),
    where I is Discharge current = 1 x C (in Faraday)

For example, measuring the actual capacitance of ELNA, DSK-3R3H224U-HL is to set

  • V1(V)=0.8×Rated voltage E (V) =0.8 x 3.3V = 2.64V
  • V2(V)=0.4×Rated voltage E (V) =0.4 x 3.3V = 1.32V

For more capacitor technical information, check out these articles below

Attached is Elna’s testing procedure for EDLC capacitors which follows JEITA RCR-2370B standards
JEITA RCR-2370B.PDF (121.9 KB)

I tried this method for a 220mF super cap. Capacitance I get is either higher than my high limit or lower than my low limit, depending on the discharge current I’m using. In my case I used an electronic DC load in constant current and it draw 1ma since that is the minimum I can get from the electronic DC load. (The .22mA on the example is to small for my Electronic DC load). Still scratching my head on what can be the problem.

The accuracy of such a load at the lower end of its operational limits may not be all that good. Verifying that it’s doing what you think it’s doing would probably be a good starting point.

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