Float Operation Research Articles

Influence of float and charge voltage adjustment on the service life of AGM VRLA batteries depending on the conditions of use

Valve-regulated lead–acid (VRLA) batteries with absorptive glass mat (AGM) separators have been in use for over 20 years in different standby applications. These applications are increasingly varied, especially regarding environmental conditions. Standby batteries are not only for use in applications where conditions are strictly defined and controlled (air conditioning) and it is therefore necessary to review and clarify the key parameters for the use of VRLA batteries with respect to the optimum conditions. Several series of chemical and electrochemical reactions occur in VRLA batteries particularly when in a charge or float charge condition. These reactions give specific properties such as minimal water loss (low maintenance) but also create specific precautions for use. VRLA battery functioning is limited by four main phenomena that are positive grid corrosion, irreversible active mass sulfation, active mass degradation by cycling and dry-out by loss of water. Positive grid corrosion is the usual failure mode in float operation or due to persistent overcharge. Irreversible active mass sulfation occurs due to lack of charge. In cycling, dependent upon the frequency and depth of discharge, the active mass undergoes numerous structural changes that cause degradation. These four limiting phenomena define a framework inside which several parameters determine the service life of VRLA batteries. These parameters are commissioning, temperature, and frequency and depth of discharge. Commissioning is necessary to equalise and fully charge the cells before use. Temperature, and temperature dispersion, is the main factor determining the rate of corrosion. The frequency and depth of discharge determine how the active mass is utilised. This paper, by considering these parameters both qualitatively and quantitatively, attempts to indicate how and why to adjust the charge and float voltages to optimise the use of AGM VRLA batteries according to the environmental conditions.

Performance of valve-regulated lead/acid test cells for float operation using modified positive active materials

Three types of valve-regulated lead/acid cells have been made with positive active material prepared from: (i) tribasic lead sulfate; (ii) tetrabasic lead sulfate; (iii) tetrabasic lead sulfate with graphite added. The cells have been subjected to float operation. They undergo premature capacity loss. The circumstances of this effect, the possibility of recovery of the capacity, the role of the graphite, and the impedance spectra of the cells are discussed.

Investigations into the electrochemistry of recombinant, sealed lead/acid batteries

In modern stationary and cycling operations of lead/acid batteries, gas-recombination technology is being used more and more frequently to eliminate battery maintenance. Research studies in the Central Laboratory of Batteries and Cells (CLAiO) are focused on the optimization of the gas-recombination process in lead/acid batteries, mainly in float duties. This work includes investigations of the kinetics of gas evolution on different types of alloy, and of the effect of paste composition and the method employed for electrolyte immobilization (i.e., gel or absorptive glass-mat). Tests have been performed on stationary cells of 4.5 A h capacity ( C/10) and using grids of size 66.0 mm X 96.5 mm. The grids were made from low-antimony alloy (1.7 wt.% Sb), lead—tin—calcium—aluminium alloy, or pure lead. Investigations of the gas-evolution kinetics has confirmed that during the initial phase of float operation, the lowest gassing is observed for nonantimonial and pure-lead grids in cells using absorptive glass-microfibre separators. Higher rates of gas evolution take place in cells with gelled electrolyte, but these decrease as the float operation is continued. Cells have been dismantled in order to investigate changes in the phase composition of the positive active material. Changes in phase composition of the active material during float operation have been monitored by X-ray diffraction phase analysis.

Lead-Acid Battery: Float Behavior of the Lead-Acid Battery System

We discuss in this article the requirements for satisfactory float operation of lead-acid batteries and analyze behavior during float in terms of the kinetic parameters which characterize the electrochemical processes occurring in the overcharge region. We show how knowledge of these parameters may be used to estimate whether adequate battery maintenance can be expected under specified float conditions. The results emphasize the need for cell uniformity, and the treatment provides a basis for determining what variability is permissible.