Recharging VRLA batteries for maximum life

This paper shows how the conventional method for floating, charging and recharging VRLA batteries with the power plant rectifiers/battery chargers has limitations. Accelerated dry-out of the battery can occur thus reducing the life of the battery and create conditions favorable for thermal events. The culprit is the combined full output current capacity of the rectifiers/battery chargers in a power plant. The accepted objective of the rectifiers/battery chargers is to return the load bus and the batteries to the float voltage setting as quickly as possible. A vast majority of the DC power plants in operation today have a charging capacity excess, including the redundant rectifier, which can deliver full output current at recharge (the period following the return of AC power after a discharge of the batteries). The paper shows how a controlled recharge of the VRLA batteries can return the battery to its full capacity with minimal dry-out and no risk of a thermal event. Control of the amount and rate of current delivered to the battery during recharge can be achieved through power electronics. Methods for new and existing installations are discussed with cost effectiveness addressed. The paper utilizes test data to show the different recharge results and how the different recharge regimes compare. Included in the paper are tables and corresponding graphs to show the differences in the methods of recharge. The paper compares the relative merits and drawbacks of the different regimens of recharging