Increasing UPS battery life main failure modes, charging and monitoring solutions

Abstract

Uninterruptible power supplies (UPS) are increasingly considered to be a reliable and cost effective solution for providing protection and battery back-up for both private and public telecommunication infrastructures. The purpose of this paper is to examine some of the factors that are important for reliability and longevity of VRLA batteries in a UPS. After discovering that the main cause of battery failure was overcharging, we concentrated on finding the best method for managing UPS batteries. We came to the conclusion that, in order to improve drastically the reliability and longevity of the UPS batteries, we have to choose pulsed charging and cell by cell monitoring, taking into account a small but suitable set of parameters. Pulsed charging allows us to adjust more accurately the amount of current delivered to the battery during the sustained charging phase compared to the traditional float mode. Several methods are available for pulsed charging: selection of the right pulsed charging mode is a key factor in obtaining the lowest stress level for the battery. Cell by cell monitoring is known to be one of the best ways to manage batteries because it allows us to take into account the spread of production performance of the different battery blocks which are generally included in a string. Furthermore it allows us to identify weak cells in the customer installation blocks. This paper describes the UPS battery failure modes and the MGE recommended solutions to use in order to reduce the failure effects. It describes the parameters we think are most suitable to monitor the battery, particularly in the case of pulsed charging.