The initial voltage drop in lead–acid cells: the influence of the overvoltage

The initial voltage drop at the switching on process in lead–acid batteries used as UPS may cause the breakdown of the battery and the failure of the external load when this operates within low fluctuations of the set-up voltage. One of the main components of the initial voltage drop is the overvoltage, whose effects can be considered more important than the ones caused by the electrolyte resistance and other contributions. The use of electrolyte circulation has proved, especially at high rate discharges, to reduce the overvoltage, thus the influence onto the initial voltage drop, and the risk of a sudden breakdown. The voltage drop caused by the overvoltage has been reduced with the use of the electrolyte circulation at high rate discharges, by 57% to 79%, depending on the current rate. Besides, the number of elements required in the battery block to meet the external load demand has been reduced, on average, by 6% to 12% depending on the maximum fluctuation allowed in the external load voltage. The energy required to recirculate the electrolyte, which is taken from the own battery, is overcompensated by the saving of energy because of the reduction of the voltage drop, with an excess of energy of up to 20%, for the heaviest working conditions of the external load.