Equalisation of Lead-Acid Stationary Cells

Lead-acid stationary cells of three types, all with Pb-Ca alloy grids, have been float charged in strings of four or five cells for nearly two years. Individual cell potential differences have been measured during floating at 2.2 V/ cell, during equalisation at 2.35 to 2.4 V, and during periods on open circuit. The potential difference across a cell has been taken as an indicator of its health, following Milner, a high float voltage being preferred to a low one. Three modes of equalisation have been attempted: (i) raising the P. D. of all cells in a string to ca. 2.35 V/cell, (ii) raising the P. D. of one cell in a string to 2.35 V using a second power supply in parallel with that maintaining the other cells at 2.15 to 2.2 V each, and (iii) raising the P. D. of one cell to 2.35 V using a separate power supply, treating this cell in isolation from other cells in the string. Only the last method appears to be without drawbacks.