Vehicle lead-acid battery state-of-charge meter

We describe a state-of-charge, or “residual-capacity” meter for lead-acid batteries that intelligently synthesizes coulometric and terminal-voltage methods in a new algorithm to provide reliable, continuous readout of remaining capacity. Novel electronic circuit design eliminates the need to install a shunt in the vehicle. The meter learns the characteristics of a battery to which it is attached, removing the need for setup, customisation, programming or calibration at time of installation or battery replacement. The meter can thus be installed by unqualified personnel. Initial measurements suggest the design to be robust and accurate.

I. Introduction

ELECTRIC vehicles are expected to have an equivalent of the fuel gauge that appears on the dashboard of vehicles powered by liquid fossil fuels. This proves to be difficult as there is no readily-measured material being consumed as in the case of a fossil-fuel vehicle. A number of approaches have been reported in the literature and a number of products are available on the market, but the complexity of the processes even in the widely-used and well-studied lead-acid battery have thwarted the development of a gauge that finds acceptance and works well in the field.