GB1227915A - - Google Patents

Abstract

1,227,915. Charging batteries. McCULLOCH CORP. 29 April, 1969 [2 May, 1968], No. 21658/69. Addition to 1,219,324. Heading H2H. A method of charging a battery, such as a battery of sealed nickel-cadmium cells, comprises the steps of alternately charging the battery at a high rate and discharging it into a load, the signal controlling the change-over being derived as an integral of the terminal voltage of the battery. A circuit for charging a battery 1 comprises an A.C. source 12 rectified by diodes 6, 7 to produce a pulsating direct current by means of which the battery is charged by way of a normally closed contact 3 of a relay 14 and the bimetal element 27 of a thermal switch 25, the rate of charge being of the order of eight times the nominal one-hour rate of the battery. The battery voltage is sensed by means of a potential divider 17, 18, 19 and used to charge a capacitor 15 forming part of a relaxation oscillator 5. As the terminal voltage of the battery 1 increases, the charge acquired by the capacitor 15 increases until it reaches a value at which a thyristor 21 is gated on to energize the relay 14. Energization of relay 14 opens contact 3 to terminate the flow of charging current and closes contact 4 to connect the thermal switch 25 across the battery whereupon a high discharge current is taken from the battery. A contact 26 of the relay 14 also closes to discharge the capacitor 15 so that the gating signal for the thyristor 21 is removed. The relay 14 remains energized by virtue of a capacitor 23, the duration of the discharge period being determined by the size of this capacitor. After the relay 14 has dropped out and contacts 3, 4, 26 returned to the normal positions the charging and discharging cycle repeats, the frequency of the operation increasing as the battery terminal voltage increases. Charging of the battery is terminated when the battery voltage reaches a value at which the bimetal element 27 opens during a discharge period. This element is resettable manually. In a second embodiment, the relay is replaced by solid state components and the discharge circuit includes part of the transformer 9.