Discharge Test to Detect Unbalancing in Electric Vehicle LiFePO4 Battery Pack

Lithium Iron Phosphate (LiFePO4) battery is regarded as a promising technology for electric vehicles (EV) because of its advantages. To meet power and energy requirements and increase the pack capacity, cells in a battery module or battery pack are often electrically connected in series or series-parallel. In a battery pack system, cell imbalance always occurred. In this study, the discharge process on the LiFePO4 battery pack under different discharge current was evaluated to know the effect of discharge current on balanced cells in the battery pack. This test will permit us to evaluate the amount of balancing current among cells needed to obtain optimal balancing time and maximize battery life and performance. The test was carried out on a 15S1P battery pack comprising 15 LiFePO4 battery cells with 200 Ah capacity. The experimental results show that the voltage difference between the highest and the lowest cell was 301.3 mV, 269.8 mV, and 239 mV with a discharge current of 50 A, 100 A, and 150 A, respectively. Based on the experiments, it was found that the greater the discharge current, the smaller the voltage difference between the highest and the lowest cell.