Abstract

If a battery of rechargeable nickel-cadmium cells discharges too fast there is a risk of reverse-charging some of the cells. Should even one cell reverse-charge, normal recharging will not restore the battery to its rated capacity. Other effects that can be expected are gas venting through the seals and even the possibility of permanently damaging the cells. A load remover that discharges the battery continuously but slowly, after it disconnects the load, will protect the battery, particularly if it is in a portable instrument. A simple load-remover circuit is not suitable because it lets the battery discharge only partially and then removes the load completely. And cutting of all current in a partially-discharged nickel-cadmium unit leads to yet another source of degraded performance, left double quote memory effect right double quote . In addition when cell voltages left double quote rebound right double quote (output voltages rise upon load removal) there is a tendency to reconnect the battery and load so that a slow oscillation of the output, caused by the control circuit, results. Putting hysteresis into the load remover protects the battery from being reconnected due to rebounding when the load is removed. A circuit is presented that provides the necessary continuous discharging as well as needed hysteresis.