GB1276505A - Improvements relating to automatic battery charging apparatus - Google Patents

Abstract

1276505 Battery charging systems ALKALINE BATTERIES Ltd 25 Sept 1969 [27 Sept 1968] 46044/68 Heading H2H A battery charging system is provided with a reference cell. which is charged simultaneously with the main battery, together with means for comparing the voltage of the main battery with that of the reference cell, the comparison being used to terminate or to modify the charging process. A battery 10 of the sealed nickel cadmium type is charged from a supply 12, this type of battery exhibiting a rise in temperature and a fall in terminal voltage when it is fully charged. At the same time a reference cell 20 is being charged over a circuit which includes a diode 45, transistor 15 and a transistor 40 which together with a resistor 41 forms a constant current device. The transistor 15 with a transistor 16 forms a device for comparing the voltage of the battery 10 with that of the cell 20 since the bases of these two transistors are conditioned by the battery and the cell voltages respectively. As soon as the voltage of the reference cell 20 exceeds a certain value relatively to that of the main battery 10 a transistor 28 becomes conductive whereupon the transistor 16 becomes more conductive than the transistor 15 so that the current in this transistor falls and at a certain point no further charging current flows in the cell 20. When the main battery 10 becomes fully charged the fall in its terminal voltage causes the current in the transistor 15 to fall still further whereupon a transistor 47 becomes conductive which causes transistors 51, 55 to become conductive to energize a relay 30 to open contact 30/1 and terminate the charging process. The reference cell can then be discharged by closing a switch 60 which may occur automatically at the end of the charging process. Alternatively, energization of the relay 30 may be arranged to start a timer so that the charging process is terminated a timed period after the relay has been terminated. Again, the circuit may be modified so as to be usable to charge batteries which exhibit a rise in voltage when fully charged. A further embodiment shows a relay which is energized whilst the battery is being charged which relay has normally open contacts.