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Coup de fouet effect in estimating battery state of health

Ryś Piotr Andrzej, Kaczor Krzysztof, Lipkowski Jacek, Piszcz Michał, Biczel Piotr, Siekierski Maciej

Journal of Power Technologies

2021

Vol. 101, nr 2

112--126

The coup de fouet phenomenon (crack of the whip) is a dip in the discharge voltage observable during the first minutes of the discharge period of a lead acid battery, followed by a transient recovery. This leads to the formation of an interim plateau transforming later into a typical discharge curve characteristic of a galvanic cell. The phenomenon was considered as a basis for a state-of-health (SoH) assessment, where the depth of the dip was used to measure the battery’s SoH. However, the validation process showed the two variables lacked clear correlation, mandating a revision of this approach. Therefore an attempt to correlate certain aging processes to the behavior of the cell of interest associated with the presence of the coup de fouet phenomenon was attempted for a set of diverse lead-acid battery designs. A set of estimators based on the coup de fouet was devised and their relation to the aging processes was explored and described. The research led to the conclusion that there is a direct relation between the coup de fouet and sulfation. This relation is best defined by Δ τplateau - the time taken between the voltage reaching the lowest point of the dip and then reaching the highest observable plateau voltage.

The effect of various buffer battery maintenance regimes on the state of health of VRLA batteries

Ryś P., Lipkowski J., Siekierski M., Biczel P.

Journal of Power Technologies

2018

Vol. 98, nr 4

365--376

Modern society relies on the constant flow of quality electricity. Various safety measures in the form of uninterruptible power supplies (UPS) combined with diesel generation systems are used to ensure permanent power delivery to strategic services during a power outage. Batteries UPS systems are held in buffer mode to avoid the self discharge process progressing. The impact of various buffer battery maintenance regimes is an important factor in ensuring the reliability of UPS systems. A series of tests on five battery pairs were performed to estimate the impact of five different buffer regimes on the batteries’ state of health. The tests were carried out in the span of one year, at heightened temperature to accelerate the negative impact of the said regimes on the batteries’ state of health. The test results showed that, contrary to widely-accepted belief, rippling of the buffer charging current does not have a significant negative impact on battery health. A comparison did indeed show that rippled charging current delivered lower total capacity loss than unrippled current. Then desulfation was applied to the batteries after testing to estimate the amount of capacity that was lost due to sulfation. It determined that rippling promotes more irreversible capacity loss (not caused by sulfation) than unrippled current with the same average voltage. The insights gained from these tests could inform attempts by industry to slow down the deterioration of lead-acid batteries in UPS applications.