Charge equalizing and lifetime increasing with a new charging method for VRLA batteries

Abstract

A new charging method for valve-regulated lead-acid (VRLA) batteries is presented which limits the maximum of all block voltages in a battery string. A commercially available VRLA battery was equipped with cell-pressure and cell-voltage sensors. The new charging method was applied to the battery in comparison to conventional IU-and IUIa-charging methods. Voltage and pressure measurements during these experiments show clearly that the conventional charging methods lead to excessive overcharge of single cells correlated with irreversible water losses. These problems are efficiently avoided by the new charging method. Capacity data from cycling operation prove as well that the new charging method guarantees charge-equalizing between the inhomogeneous cells while avoiding additional hardware.

Equalization requirements for series VRLA batteries

“…The degradation is caused by lack of time to bring individual cells to a consistent average voltage. In [8], passive equalization is supplemented with a firm voltagelimit: chargevoltageisalwayslimited to keep thehighest cell voltage below the target maximum. The total time to restore balance in the string in [8] extrapolates to approximately one week, but charge times of 12 h or less made imbalance worse.…”

“…Even the passive-based method in [8] will suffer from this problem, since small errors in measurements will influence the voltage limit setting and the equalization process.…”