Fuzzy Logic-Based Smart Battery State-of-Charge (SOC) Monitor for Automotive Batteries

Automotive start, light, ignition (SLI) lead acid batteries used in tanks are prone to capacity loss due to low temperatures, self-discharge, sulfation and shorting of plates. Monitoring and charge control of these batteries can be improved by using the concept of a smart battery system (SBS). In a SBS, battery data from sensors embedded in the battery package are acquired by a smart battery controller which processes this data, and transmits charge control information, to a central processor for effecting control actions over a controller area network (CAN) bus.

Smart battery circuitry has been designed, developed and implemented to monitor the SOC of a 12V automotive lead acid battery used in tanks. The hardware comprises ac impedance measuring hardware interfaced to a Motorola 68HC12 microcontroller with a built-in CAN controller interface. The SOC estimation algorithms are based on a fuzzy logic model that is directly implemented into the Motorola 68HC12 microcontroller. Details of the hardware and fuzzy logic model design will be presented.