GB1236145A - Rapid charging of batteries - Google Patents

Abstract

1,236,145. Charging batteries. McCULLOCH CORP. 14 July, 1969 [15 July, 1968; 26 June, 1969], No. 35323/69. Heading H2H. A battery is charged rapidly by high-current D.C. pulses between which the battery may be discharged for very short periods. In the circuit of Fig. 1, a battery 1 is connected to a source 2 of pulses through a thyristor 13 which is turned on when the source voltage exceeds the terminal voltage of the battery. The high current causes the battery voltage to rise very rapidly at first and subsequently to rise more slowly until the fully charged state is reached. This is signalled by the breakdown of a Zener diode 29 which triggers a further thyristor 24, thus diverting current from the gate of thyristor 13 and turning it off. A trickle charge may then flow through a lamp 28. Directly across the battery terminals, there is connected a transistor 4 which can be switched on briefly by a timing circuit 5 responsive to the battery voltage. When the transistor is switched to its conductive state, a large discharge current flows from the battery. Preferably, the discharge period lasts about 2 microseconds, this time being the period of a highfrequency signal which is stated to occur as a result of a resonance effect in the battery. An inductor 19 ensures that discharge occurs only when the thyristor 13 is blocked. During the initial charging period, discharge occurs at the rate of perhaps once a second, the rate increasing as the battery charges. During a discharge pulse, the terminal voltage momentarily decreases by about five volts. The thyristor 24 may be in thermal contact with the battery so that any excessive temperature rise causes charging to be cut off. In a further embodiment, Fig. 7 (not shown), the transistor 4 is replaced by a pair of cascade connected transistors and the circuit is compensated for temperature variations by the inclusion of a thermistor.