Nickel-cadmium batteries as capacitive filters for pulsed loads

This investigation consisted of several tests of specially fabricated nickel-cadmium batteries having circular disk-type electrodes. These batteries were evaluated as filter elements between a constant current power supply and a 5 Hz pulsed load demanding approximately twice the power supply current during the load on a portion of the cycle. Short tests lasting 10,000 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 J/lb. In addition, two batteries were subjected to 10 million charge/discharge cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode-to-battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 J/lb, respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10 million cycles, capacity degradation was negligible for one battery and about 20 percent for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed.