The art of impedance testing

Impedance testing of batteries has reached its next plateau. Battery manufacturers are using the impedance method to do routine testing of cells in the factory and in field studies. The method provides sufficient information to determine the weak cells in a string of the same production lot. When used at the time of the initial installation, damage that occurs from skipping may be identified. The study shows the interrelationship of impedance values, ampere-hour capacity and the type of cells used for different applications. Baseline impedance data can be developed from impedance measurements performed on older battery systems. In addition, capacity can be estimated from a few single cell load tests by calibrating the impedance data. IEEE 1188 recognizes ohmic measurements as an alternate test method when load testing is not performed on VRLA cells