Effects of charging algorithm and converter topology on energy efficiency

Underground mining activities in South Africa depend on battery fed underground locomotives to haul ore. The batteries are predominantly lead-acid and have to be charged periodically. At the moment, most of the battery chargers in use in South African mines are based on ferroresonant or transductor charger technology. At the same time, the charging algorithms in use are time based and in general without a clearly defined equalization phase and charge termination criterion. This paper will show that by utilizing a charging algorithm with a clearly defined gassing and equalization phase, it is possible to significantly reduce total energy consumption in a charging bay. Further, the use of switch-mode chargers can have the desirable effect of increasing total power factor and hence lower the maximum kVA demand.