GB912666A - Improvements relating to the regulation of the charging of secondary cells - Google Patents

Abstract

912,666. Charging and discharging batteries. HARMER, H. M. May 29, 1961 [June 9, 1960], No. 20349/60. Class 38 (4). The charging current of a battery 4 is controlled by a temperature-sensitive switch 1 disposed adjacent to a catalytic device 2 in a cell 3, so that during gassing a predetermined temperature rise of the device 2, produced by the current which electrolyses the water content of the electrolyte, causes the switch 1 to open and interrupt the current or reduce it by a resistance 6, until a fall of temperature allows the switch 1 to reclose. The current may be controlled by a relay and contactor operable by opening or closing of the switch 1 and connected in the input or output side of the charging unit 5, a resistance and/or reactance being included if only current limitation is desired. Two or more temperature-sensitive switches may be associated with one catalytic device to operate at the same or different temperatures and provide more than one change in the charging operation. Each cell of the battery may have a catalytic device and switch, the switches being connected in series or parallel and, if two switches are provided in each cell, one set may be in series and the other in parallel. A single switch per cell arrangement may have means to indicate a faulty cell, catalytic device or switch, Fig. 2 (not shown). In an alternative arrangement for reducing the charging current, Fig. 3 (not shown), each cell is in parallel with a normally-open switch in series with a resistor, which may comprise a diode or diodes whose voltage/current characteristic ensures a substantially constant voltage across the cell. If two switches are fitted to each cell then the arrangements of Figs. 2 and 3 may be combined. With A.G. supply to the charging unit changes of resistance in the output side caused by operation of the switch(es) may be transferred to the input side through transformer(s) or transductor(s). Alternatively, the switches may control gated diodes or transistors. The arrangements described above may be used in conjunction with the arrangements described in Specifications 912,664 and 912,665, the switch being used to bring into circuit the temperature-sensitive resistor or the thermo-couple, or to give warning of the failure of the control means described in these applications. When used with existing types of charging systems, the contacts of the switch or switches may be connected in the input circuit of the charging means or at some intermediate point in the charging means. As the battery approaches full charge, use can be made of the decreasing periods for which the charging current is flowing to disconnect the charging system entirely from its supply, either by means of a timing device or after a pre-arranged number of switching operations. The combination of catalytic device and temperature-sensitive switch may be used to indicate or control abnormal gassing conditions in the cell, such as over-rate discharge. Specifications 693,096 and 871,605 also are referred to.