The performance of Pb-acid cells linked to supercapacitors under partial state of capacity cycling conditions

A comparative study was done based on the charge acceptance of small valve regulated Pb-acid cells at different states of charge (SoC) with a parallel configuration of supercapacitors at 1.4, 5.0, 10.0, 21.4 and 31.4 F/A h ratios. The study found that a hybrid system of a Pb-acid cell that was charged at a constant voltage with a relatively small supercapacitor configuration resulted in a significant improvement in both the peak current as well as the charge acceptance current over a 5-s period. The cell configuration at 20% SoC with a 31.4 F/A h capacitor showed the largest improvement, where a charge acceptance current of 16 times in magnitude was observed in comparison to a cell with no supercapacitor. A 12 V battery was assembled with cells at different SoC where each cell was linked to a supercapacitor in parallel. The battery showed that there was a significant improvement in its partial state of capacity cycle (PSoCC) ability with a 5 times increase in the number of achievable cycles for the first cycle unit when compared to a similar battery with no supercapacitor. There was also an improvement in maintaining the C20 capacity that followed each PSoCC test unit. By monitoring the individual cell voltages, the main cause of failure was the 'weakest link' cell at the lowest SoC that was significantly over-charged during the PSoCC sequence and subsequently over-discharged during the C20 capacity tests. A significant improvement in the charge acceptance and cycle-ability of a Pb-acid battery can be achieved by a simple parallel configuration with modern supercapacitors.