Load sharing improvement in parallel-operated lead acid batteries

A battery is the device that transforms chemical energy into direct-current directly without a mechanical process. Unit cells are connected in series to obtain the necessary voltage, while being connected in parallel to organize capacity for load current and to decrease the internal resistance for corresponding the sudden shift of the load current. Because the voltage drop in parallel battery sets in unequal, low efficiency of power converter and system shutdown may result. However, when the system is being driven in parallel, a circular-current can be generated. The charging current differs in each battery set because the system, including batteries, rectifiers and loads, are connected in parallel, making the charge voltage constant. It is shown that, as a result, the new batteries are heated by over-charge and over-discharge, and the over charge current increases rust of the positive grid and consequently shortens the lifetime of the new batteries. The difference between the new batteries and old ones is the amount of internal resistance. In this paper, the authors detect the unbalance current using a microprocessor and achieve current balance by adjusting the resistance of each battery set. The internal resistance of each set becomes constant and the charge and discharge currents are balanced by inserting an external resistance into the system and calculating the change of internal resistance