METHOD AND DEVICE FOR TESTING NI-CD BATTERIES.
SIGNAL CORPS ENGINEERING LABS FORT MONMOUTH NJ
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A method was found and a device was developed to determine the state of charge of Ni-Cd cells andor batteries of the BB-401U type. The principles of the method are differential voltage readings during 1-minute charge and discharge periods at 10 and 20 amperes respectively. These voltage differences are indicative of the remaining capacity. Since the internal ohmic resistance resistance of electrolyte, electrodes, terminal leads, contact resistances between electrodes and electrolyte and the like does not have the same value for all cells, even for those of the same type and construction, and, moreover, since it changes with different capacities remaining, often during the test time itself, the voltage drop across the ohmic resistance had to be eliminated. This was achieved by charging and discharging the cell or battery to be tested with a pulsating current. The accuracy of the method is between 5 and 10 of the full capacity, depending on the state of charge. Tests on half-charged cells have the lowest accuracy.