Development of Optimized Fast Charge Algorithms for Lead Acid Batteries 1999-01-1157

Recent studies have demonstrated that fast charging techniques can significantly extend the effective daily range of lead acid battery powered EVs. Further, other research has shown that the total lifetime energy delivery of suitable VRLA batteries can be increased markedly through partial state of charge cycling. A research team composed of Arizona Public Service (APS), CSIRO Division of Minerals (CSIRO), Electric Transportation Applications (ETA), and Hawker Energy Products, Incorporated (HEPi) has been assembled to conduct a detailed laboratory and field program to develop operating regimes that will improve lead acid battery performance in EV applications using fast charge and PSOC operation. Research is being conducted under the cognizance of the Advanced Lead Acid Batttery Consortium, both in the laboratories of CSIRO and HEPi, and in the electric vehicle fleet of APS and ETA.

Initial field testing of Hawker Genesis® 12 volt, 38 Ah modules in a US Electricar S 10 pick up truck has provided very encouraging results. The vehicle was charged using a 150 kW Norvik Minit® Charger at a maximum current of 165 amperes (5C at the 33 Ah C₁ rate for the Hawker Genesis® modules). The vehicle was operated three to four cycles per day from about 20% to about 80% SOC. The battery pack delivered a total of 15,258 Ah (462 times the 1C rate) in accumulating 16,846 miles on the S10 test vehicle. Initial laboratory testing has focused on maximum charge rates and the temperature effects of hyper-charging (rates greater than 9C) lead acid batteries. Charge rates of 29C were found to fully charge Hawker Genesis® 12 volt, 13 Ah modules. However, the highest practical upper charge limit was 11C, as temperature effects presented an upper limit on practical fast charge rates. Preliminary testing has shown the combination of fast charging and partial state of charge operation in EV batteries to be very promising in terms of increasing both cycle-life and effective vehicle range.

This paper details the results of initial project testing and concludes that temperature effects present an upper limit on fast charge rates and that preliminary testing indicates very beneficial resutls are obtained by the combination of fast chrging and partial state of charge operation in EV batteries.