A miniaturized tester for detecting weak individual cells in Ni/Cd batteries

Reliability of battery powered equipment is only as good as the reliability of the power source itself. One way to ensure the reliability of a nickel/cadmium power source is to periodically test the battery under given load conditions and study the reaction. After loading the battery for a specified period of time, a pass or fail determination can be made by comparing the loaded voltage of the battery under test to the expected voltage of a healthy battery subjected to the same test. Most batteries are made up of individual low voltage cells connected together in series to achieve a higher voltage, and it is often only a small number of individual cells that cause a battery to fail the test. Even so, substandard batteries are replaced in their entirety at a substantial cost. A low cost, miniaturized, constant resistance tester has been developed to determine which individual cells in a battery are weak. This is accomplished by automatically loading the cell under test and comparing the final loaded voltage to a preset value. Individual cells found to be substandard may then be replaced at a cost savings to the owner of the battery. Based on parameters specified by the user, the tester can be configured to test individual cells with different capacities and even small battery packs. Results of prototype field tests are presented.<>