STATE OF CHARGE INDICATORS FOR NICKEL CADMIUM BATTERIES

Abstract : THE VARIATIONS OF SEVERAL ELECTRICAL PROPERTIES OF NICKEL CADMIUM CELLS WITH STATE OF CHARGE WERE STUDIED TO DETERMINE THE SUITABILITY OF ANY OF THESE FOR MEASURING STATE OF CHARGE. Three methods were originally proposed: measurements of ohmic resistance, microsecond transients and double layer capacitance. During the investigations two additional parameters were measured, a. c. impedance and phase shift. Double layer capacitance and a.c. impedance and transient behavior are not useful properties for determining state of charge. A phase shift system is described which when properly calibrated predicted state of charge with an average deviation of = 10%. Ohmic resistance measured under correct conditions showed a closer correlation to state of charge but is difficult to measure.