Patent GB-1495523-A (GB)
Title: Automatic electric battery charging apparatus
IPC: H02J7/10
Filed: 1974-02-26
Abstract: 1495523 Battery charging systems CHLORIDE GROUP Ltd 24 Feb 1975 [26 Feb 1974] 8591/74 Heading H2H An automatic battery charging apparatus including means to provide a taper charging characteristic is provided with means for terminating a phase, at least, of the charging process when the rate of rise of a control signal used in the process falls below a predetermined value, the control signal being the difference between signals dependent upon the battery voltage and the A.C. supply voltage compared with a reference signal which reference voltage is increased step-wise whenever the control signal exceeds the reference signal. A battery 6 is charged by a unit 13 comprising a transformer and a rectifier connected to an A.C. source 1 by way of a contactor 2 which is operable by a relay 7, operation or not of the relay being indicated by lamps 37, 38 respectively. The charging unit 3 also supplies a voltage doubling circuit 35 and a mains voltage unit 27 is connected to the A.C. source 1, the unit 27 comprising a circuit which provides a signal 26 dependent upon the A.C. voltage 1. When a battery 6 is connected to the charging terminals 4 a voltage stabilizing unit 36 connected thereto provides a stabilized D.C. voltage to energize the logic circuits of the apparatus. Gate circuits 30, 31, 32 sense the battery voltage, which voltage is also fed to a network 24 by a signal line 25 in which network the battery signal 25 and the A.C. mains signal 26 are compared to produce a control signal 23. If the gate 30 senses the battery voltage to be below 1À80 volts per cell, the signal therefrom to the initial delay circuit 12 allows the unit 12 to produce an output signal 9 which by way of a gate 8 inhibits operation of relay 7 to close the contactor 2 until the delay unit 12 times out after which the relay 7 operates and the lamp 37 lights up to indicate that the contactor 2 is closed so that the charging unit 3 beings to charge the battery. The control signal 23 from the network 24 is compared in a comparator unit 22 with the output signal 17 of a digital to analogue (D-A) converter 15 fed with digital signals from a binary staircase generator 14 which receives signals from a clock 18. The clock 18 is under control of the output signal 28 of the comparator unit 22 the clock 18 producing clock signals only when the control signal 23 exceeds the staircase signals 17. Thus, whenever, as the battery voltage rises during charging, the control signal 23 exceeds by one step. The time interval between the step buildup of the staircase signal 17 gives a measure universely proportional to the rate of increase of the battery voltage 25. The staircase generator is resettable by a reset circuit 21 and a gate 29 inhibits operation of the clock 18 when the A.C. source is not connected to the apparatus. When ever the battery voltage rises above 2À35 volts per cell the gate 31 produces a signal 40 which starts a clock 32 which delivers clock pulses to an interval timer 13 such that, should the timer 13 reach a specified count before a reset signal 19, indicating the beginning of a step in the staircase signal 17, is received in the timer 13 a signal 10 is produced and fed to the gate 8 to de-energize relay 7 so terminating the charging process. At the same time lamp 37 goes out and lamp 38 switches on to indicate the end of charging. Should the count in the staircase generator 14 exceed a maximum, a signal 11 is produced, which by way of gate 8 also terminates charging. If, during charging, the battery becomes disconnected, the voltage doubling circuit impresses a voltage higher than 3À40 on the logic circuits which is sensed by gate 33 so as to trip a trigger circuit 34 to re-activate the delay circuit 12, the signal 9 from which activates gate 8 to open relay 7 and the contactor 2 to end the charging process. In Fig. 1 the line 70 represents the battery voltage during charging, the line 71 the control voltage (23) and the line 72 the staircase signal (17).