Patent GB-912665-A (GB)
Title: Improvements relating to the regulation of the charging of secondary cells
IPC: H02J7/00
Filed: 1960-03-24
Abstract: 912,665. Battery-charging systems. HARMER, H. M. March 15, 1961 [March 24, 1960], No. 10449/60. Class 38 (4). Reduction of charging current of a battery 1 from a maximum value to zero is made temperature dependent on a catalytic device 8 provided in the battery for converting oxygen and hydrogen evolved during charging into water, by means of a temperature sensitive resistor 9 in thermal contact with the device and which controls the triggering and hence duration of the conductive period of gated diodes 4 supplying the charging current. Battery 1, one cell of which contains the catalytic device 8 and a negative temperature co-efficient resistor 9, is charged from an A.C. supply 2 by means of a centre-tapped transformer 3, the primary winding of which is in series with an inductance 7 which may be a gapped-cored inductance, a transductor, or may be provided by leakage reactance of the transformer. The temperature-sensitive resistor 9 is connected in series with a paper di-electric or reversible electrolytic condenser 10 across a small centre-tapped reactance or transformer 11 which is itself connected to a secondary winding 13 of the transformer 3 through an inductance or transductor 12. The maximum current to the diode gates is limited by resistors 14. The resistor 9 controls the valve and phase relationship of the voltage across it and the condenser 10 with respect to that supplied by winding 5 to the gated diodes 4. If the resistance is high relative to the reactance of the condenser 10 and inductance 12, then the voltage across it will be substantially in phase with that of winding 5 and the diodes 4 will be triggered so as to be conductive over nearly the whole half-cycle period over which the voltage developed to half the winding 5 exceeds the battery voltage, the charging current then being only limited by the inductance 7. As charging progresses and the temperature of the catalytic device rises, the voltage across the resistor 9 and condenser 10 will increasingly lag and hence the diodes will be conductive for a decreasing period of each half-cycle. The components 9, 10, 12, 13 may be chosen so that the mean charging current will finally approach or become zero until the catalytic device 8 has again cooled. The gated diodes 4 may be protected from high reverse voltages and those having harmful phase relationship, by the addition of two power diodes connected in series with them so as to conduct in the same sense as the respective gated diodes, and the addition of two further diodes connected across them so as to conduct in the reverse sense. A Zener diode 16 in series with a heating resistor 15 in thermal contact with the resistor 9 and connected across the battery 1, is arranged to break down at a voltage just below that at which damage might occur to the battery 1. Current which flows at break down through resistor 15 and which may be amplified by a transistor will heat the resistor 9 and hence cause the charging current to be reduced. In order that a Zener diode having any convenient break down value may be chosen, a potential divider resistor may be used, a portion of which may be temperature-sensitive so that the maximum voltage permitted will be ambient temperature dependent. In a further modification, the resistor 9 additionally serves as the heating resistor. In order that the winding 5 may be more fully utilized and its maximum output voltage increased, the windings centre tap may be omitted and the battery supplied from a rectifier bridge consisting of two gated and two power diodes. In any of the above circuits, a transistor or valve amplifier may be used to amplify the catalytic device temperature-dependent current. Specifications 871,605 and 912,664 are referred to.