Classical equivalent circuit parameters for a double-layer capacitor

As an emerging technology in the area of energy storage, the double-layer capacitor is a promising device for certain niche applications. The double-layer capacitor is a low voltage device exhibiting an extremely high capacitance value in comparison with other capacitor technologies of a similar physical size. Capacitors with values in excess of 1500 F are now available. In slow discharge applications on the order of a few seconds, the classical equivalent circuit for a double-layer capacitor, composed of a capacitance (C), an equivalent parallel resistance (EPR), and an equivalent series resistance (ESR), can adequately describe capacitor performance. The focus of this work is the determination of these parameters for four different capacitors from discharge data using standard laboratory equipment such as an oscilloscope. Capacitance values are calculated using a change in stored energy approach which allows determination of an initial capacitance, a discharge capacitance, and variations in capacitance with voltage. The sensitivity of ESR and capacitance to charge rate and initial charge voltage is also reported.