Float current monitoring and evaluation

This paper discusses the task of measuring battery charge, discharge, and float current from a single input. Additionally, detection of the float condition and historical data requirements are covered. Marconi Communications Inc. has developed a method of measurement that furnishes the entire solution of battery current measurement using a single analog input. This paper also discusses the results of a field trial of the Marconi float current monitoring system. First, a reliable reading must be obtained. Since float current is several orders of magnitude less than that of charging and discharging current, the resolution of the measurement must be very high. It is this first step that has eluded monitoring products to date. Next, the system must determine that the measurement is a float current versus a small charge current (discharge currents are distinguishable by their polarity). Marconi Communications Inc. has employed a simple and reliable method for detecting the float condition. This algorithm has been tested against data recorded during the field trial and has proved to be effective in detecting the float condition. Finally, historical data must be recorded for determining age and health of the battery. Once the float condition is detected, it is essential to record a history of the readings. It is this history that gives meaning to the measurement. By viewing this history, a user can monitor the gradual or sudden changes in the float current of the battery and interpret these changes accordingly