Tag Archives: capacity drop

1178-1189 S. Papezova and V. Papez
Battery capacity drop during operation
Abstract |
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Battery capacity drop during operation

S. Papezova¹* and V. Papez²

¹Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamycka 129, CZ165 21 Prague 6 ˗ Suchdol, Czech Republic
²Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Electrotechnology, Technicka 2, CZ166 27 Pague 6, Czech Republic
*Correspondence: papezovas@tf.czu.cz

Abstract:

A lithium-iron-phosphate (LiFePO4) battery is nowadays considered one of the best types of batteries. The paper deals with the evaluation of the drop in their capacity during operation. Based on the physical analysis of charging and discharging processes, a mathematical model of the battery capacity has been developed during its lifetime. The decrease in capacity during battery operation is evaluated according to the loss of active material, which gradually diminishes due to a number of different processes. The analysis of the loss of the active material is carried out, in particular, according to the depth of discharge, battery temperature, charging and discharging time, including the time when the battery is out of service. The tests were performed on the Winston Battery, Calb, Thunder Sky and Sinopoly batteries by cyclic discharging and charging at the 50%, 90% or 100% depth of discharge. Their real parameters were determined, compared to the model parameters and the parameters specified by the manufacturers and suppliers. Two automated systems were used for testing. During the test, in the tested battery with several cells, charging and discharging by a constant current were carried out automatically. Operating parameters of the tested battery were continuously scanned, recorded and evaluated by the control computer. The capacity curves during the battery operation, determined by the type of models, were compared with the results of long-term real battery tests.

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1152–1161 S. Papezova, and V. Papez
Endurance LiFePO4 battery testing
Abstract |
Full text PDF (335 KB)

Endurance LiFePO4 battery testing

S. Papezova¹,* and V. Papez²

¹ Czech University of Life Sciences in Prague, Faculty of Engineering, Department of Electrical Engineering and Automation, Kamycka 129, CZ165 21, Prague 6 ˗ Suchdol, Czech Republic
² Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Electrotechnology, Technicka 2, CZ166 27 Pague 6, Czech Republic
*Correspondence: papezovas@etf.czu.cz

Abstract:

A lithium-iron-phosphate (LiFePO4) battery is nowadays considered one of the best types of batteries. Manufacturers and mostly suppliers indicate that LiFePO4 batteries have much longer lifespan than other batteries, and thus convincing their customers of lower operating costs than at other types of batteries, although their purchase price is several times higher. In connection with the problem of replace Pb batteries in the backup sources of security systems with LiFePO4 batteries, there has been necessary to determine the real parameters of available cells under conditions in which they operate. The paper describes the battery tests, in which their real parameters, comparable with the parameters indicated by the suppliers, are tested. The tests lie in automatic long-term cyclical charging and discharging of the multi-cell battery. Operating parameters are continuously monitored, recorded and evaluated by the computer. Individual cells are equipped with balancers and protection circuits that prevent from exceeding the maximum voltage during charging, as well as the voltage drop below a minimum level during discharging. The results of long-term tests on LiFePO4 WB-LYP40AHA Winston Battery are presented. The first test was conducted with 100% depth of discharge (DOD). New cells, after the first charge and discharge, showed the capacity about 115% of the rated capacity, the capacity drop c. 0.015 to 0.02% per cycle and the capacity drop to 80% after 950 cycles, which represents a lifetime of about 5% less than state the manufacturers.
A second test was conducted with 50% depth of discharge. Here, again after the first charge and discharge, new cells exhibited the same capacity as in the first case, i.e. c. 113% of the rated capacity. After 1,000 cycles, the cell capacity decreased to 107% of the rated capacity, which corresponds to the expected lifetime of 5,000 cycles.

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