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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.

Battery state of charge meters based on combining fuzzy logic analysis and either Coulomb counting or battery impedance measurements have been designed, fabricated and tested. The Coulomb counting meters have been implemented in digital hardware using Motorola 68HC11 and 68HC12 microcontrollers and in field programmable gate arrays. The impedance meter has been prototyped in analog hardware using discrete components. In this paper, we present the hardware/software designs for these meters and some test results on primary Li/SO2 cells.