Experimental Evaluation of the Charging and Discharging Characteristics Of LITHIUM IRON PHOSPHATE Batteries Under Different Charging Current Conditions with Constant Load Discharge

Author

Ikebuaku Ugochukwu Solomon, Ayalo Jonathan, Jennifer Kyari-Ayele

Abstract

 This study experimentally evaluated the charging and subsequent constant-load discharge characteristics of a 12.8V, 30Ah, four-series-cell lithium iron phosphate (LiFePO4) battery pack. The pack was protected by a 4S, 40A battery management system and supported by a 6A active balancer. Charging was performed with a constant-current/constant-voltage arrangement consisting of a 15V switch-mode power supply and an adjustable buck converter set to 14.4V. Three charging-current conditions were investigated: 5A, 10A and 15A, corresponding to approximately 0.17C, 0.33C and 0.50C. After each full charge and a one-hour balancing/rest period, the battery was discharged through an approximately 5A direct-current resistive load. Voltage, current, state of charge, time and discharge temperature were recorded. Trapezoidal integration was used to estimate charge input, delivered ampere-hour capacity and delivered watt-hour energy. Charging time decreased from 385 min at 5A to 205 min at 1 A and 142 min at 15A, representing reductions of 46.8% and 63.1% relative to the 5A condition. However, the measured constant-load discharge duration decreased from 300 min after 5A charging to 250 min and 240 min after 10A and 15A charging. The corresponding delivered capacities were 25.03Ah, 20.85Ah and 20.03Ah, while delivered energies were 319.99Wh, 264.35Wh and 251.18Wh. The post-charge rested voltage also declined from 13.47V to 13.36V and 13.29V as charging current increased. Peak temperatures during the common 5A discharge remained close, ranging from 30.2°C to 30.6°C. The results demonstrate a clear time-performance trade-off in this particular battery pack and test sequence: higher charging current substantially shortened charging time but was followed by lower measured discharge duration, capacity and energy. Because each current condition was represented by a single recorded cycle, the findings establish descriptive pack-level behavior rather than statistically proven long-term degradation. Repeated randomized cycles, cell-level voltage logging, charge-temperature measurements and tighter cutoff sampling are recommended before generalizing the observed differences to LiFePO4batteries as a class.

Keywords

LiFePO4 battery, Lithium-ion battery, Battery chemistry, Charging characteristics, Discharging characteristics, Charging current conditions

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