ES348457A1 - Control of Battery Charging - Google Patents

Abstract

A load 2 may be supplied from a source 4 or, in an emergency, a battery 1, the battery being chargeable from the source 4, at a high rate when the battery is in a low state of charge and a low rate when the battery is fully charged, the transition from the high to the low rate being effected by a coulometer 11. The coulometer 11 comprises a tube containing two columns of mercury 12 separated by a quantity of electrolyte 18 which is translucent to allow light from a lamp 16 to impinge on a photo-resistor 15 when the electrolyte 13 is in the requisite place in the tube. During charging, the battery current flows through a resistor 3, the developed voltage across which is fed to the control windings of a transductor 7. An element 5 produces a stabilized D.C. voltage by means of Zener diodes, which voltage is fed to a converter 6 wherein the voltage is converted to a high-frequency alternating voltage which is applied to the A.C. windings of the transductor 7. The output of the transductor 7 is therefore dependent on the battery charging current as is the output of a rectifier 8 to which the transductor output is applied. The output of the rectifier 8 is used to control a selector unit 10 which not only controls the direction of current flow through the coulometer 11 but also establishes a shunt path (not shown in Fig. 2) around the coulometer 11 so that the magnitude of the charging current can be varied in dependence upon the battery temperature. As the electrolyte 13 moves along the tube during charging of the battery, its position will indicate the state of charge thereof and when the electrolyte is interposed between the lamp 16 and photo-resistor 15 the device 14 triggers the source 4 into its low output state whereby reducing the battery charging rate. The output of the converter 9 is also applied to a unit 9 which is connected to the rectifier 8 in such a manner as to ensure that the rectifier 8 has no output when no current is flowing through the resistor 3. When the battery is discharging the selector 10 causes the current flowing in the coulometer 11 to pass in the direction opposite to that when charging. In this case the electrolyte 13 will move along the tube in the opposite direction and its position will provide an indication of the state of discharge of the battery. The units 5, 6, 9, 10 and 14 all comprise transistor switching circuitry.