GAS-DETECTION AND MINIMIZATION OF GAS AND HEAT-PRODUCTION AT THE END OF FAST CHARGING

Fast charging of lead/acid batteries in electric vehicles has become a focal point of attention. Fast-charge algorithms depend on the accurate determination of the gassing point during any state-of-charge and are generally limited to providing 85% of the charge in a very short time. The remaining 15% requires much more time due to the low charge acceptance of the battery. This paper describes test results that indicate that with accurate determination of the gassing point and by pulse charging with a frequency and amplitude related to the state-of-charge of the battery, one can accelerate the final phase of charging. The test results show that there is a time lag between the onset of the charge reaction and the onset of the gassing reaction if a charge pulse is given to a lead/acid battery. This time lag depends on the state-of-charge and the battery charge current amplitude. The result has important implications for a fast-charge algorithm: if the current is pulsed such that it is reduced before full gassing sets in, then higher charging rates are possible during the gassing phase of the charge, at reduced gas development, by using pulse charging than would be possible with constant-current charging.