SYSTEM NOISE AS A SIGNAL SOURCE FOR IMPEDANCE MEASUREMENTS ON BATTERIES CONNECTED TO OPERATING EQUIPMENT

Alternating-current impedance measurements provide useful information about the characteristics of electrochemical systems, such as batterie s, and are envisioned as the basis for indirect methods of determining battery capacity. Impedance measurements rely on recording the respon se of the battery to a controlled current or voltage test signal. Howe ver, this type of measurement can be difficult with large batteries co nnected to operating equipment. High background noise levels, caused b y time-varying changes in the battery load, interfere with the impedan ce measurement. Instead of attempting to eliminate background noise, w e have used the noise as a test signal, in conjunction with Fourier tr ansform (FT) signal processing. The current and voltage passing throug h cells in an operating telecommunications lead/acid battery string we re determined with a simple, three-terminal connection. Impedance calc ulations were performed with a commercial FT signal analyzer. The resu lts indicate that completely passive (no externally applied test signa l, and not requiring disconnection of the string) impedance measuremen ts of batteries connected to operating equipment are feasible.