“Coup de fouet” effect in assessment of battery’s state of health

Abstract

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  tplateau – the time taken between the voltage reaching the lowest point of the dip and then reaching the highest observable plateau voltage.