Comparison of VRLA-AGM batteries lifetime charging with different currents waveforms for use on low power UPS

This paper aims to present a study of storage capacities of absorbed glass mat (AGM) valve regulated lead acid (VRLA) batteries with pulsating and non-pulsating currents charging methods. In the testing process, three batteries were charged with pulsating current, and one battery is charged with continuous current free of AC ripple. When the battery is charged with pulsed current, the RMS current is higher and it is related to the increase of internal power losses, I²R, which cause a temperature rise, and as consequence there is loss of water from the electrolyte. To show this, the charging pulse current waveforms were modeled, and both currents compared. To make the experimental tests, the UPS chargers were connected to the batteries during 24 hours, then they are removed and placed at rest mode during 3 hours, and later discharged draining a constant current of 7.2A (1C) using electronic load until reaching the minimum voltage of 9.6V. The charge and discharge tests were made up to achieve 80% of the nominal battery storage capacity from IEEE Std 1188-2014 standard recommendation for VRLA batteries replacement [1]. The capacity measurements of the battery, as a function of the number of deep discharge cycles are shown to verify the lifetime of the batteries.