Patent GB-1438290-A (GB)
IPC: H02J7/10
Filed: 1972-10-14
Abstract: 1438290 Control circuits for battery chargers WESTINGHOUSE BRAKE & SIGNAL CO Ltd 18 Sept 1973 [14 Oct 1972 11 Nov 1972 24 April 1973] 47491/72 52200/72 and 19464/73 Heading H2H A control circuit for a battery charger comprises means for timing a period during which the battery charging current is interrupted, means for registering the battery voltage decrement in a fixed interval during the interruption, means for comparing the registered battery voltage decrement with that registered earlier during a previous interruption and means responsive to the result of the comparison to permit, present or modify the charging current thereafter applied to the battery. The battery to be charged is connected to the output of a bridge rectifier D supplied with means A.C. via a transformer T1 and reverse-parallel connected thyristors SCR. A device V SIG . provides a signal dependent on the battery voltage whilst a device I SIG  provides a charging current signal. Assuming the battery to have a voltage in excess of 1À5 volts/cell but less than 2À2 volts/ cell, cell voltage sensors VS prevent a sequence controller SC from inhibiting a control circuit FAC which supplies firing pulses to the thyristors SCR. The circuit FAC enables the charging current to increase to a pre-set value I B , i.e. the bulk charge phase is operative. When the battery voltage reaches 2À35 volts, a circuit "INHIBIT 1" and a current control circuit I CON  enable the start of a taper charge phase. The 2À35 volts/ cell sensor triggers the supply of clock pulses from a generator CL at a rate of one pulse/ eight seconds to the sequence controller SC. A counter in the controller receives the clock pulses and at a count of 128, i.e. after 15 minutes, the controller supplies a signal on line I BATT  = 0 to switch off the thyristors. At a count of 132, the cell voltage signal V CELL  is supplied to a voltage controlled osicllator VCO and a timer "1000ms" enables a gate G4 to supply the pulses from the oscillator via an "UP" gate to an up-down counter N. The counter therefore digitally records the cell voltage. At the count of 134, i.e. after a further 16 seconds, the cell voltage is again measured, the previous count in the counter N being counted down by the pulses from the oscillator. A second measurement cycle then occurs, the counter N being counted down at the 132 pulse instant and counted up at the 134 pulse instant. If the resultant count in the counter N is zero1, indicating that the battery is fully charged, a detector DET causes the generator CL to supply pulses at an increased rate of 1 pulse/second to the sequence controller to mark the end of the taper charge phase. During this phase the circuit I CON , which controls the circuit FAC, receives a signal from a circuit TAPER which enables a reduction of the battery charging current as the cell voltage increases. If, at a count of 135 pulses, the counter N indicates that the battery is sufficiently charged, a "hold ready" charge phase commences when the battery voltage falls to 2À2 volts/cell. The "hold ready" charge is applied for the two minutes that the controller takes to reach a count of 128, the charge then being terminated. A protective circuit T.O.FAIL opens a switch S1 if the signal on line I BATT  = 0 indicates that no charge current should be flowing whereas the current sensor I SIG  indicates a flow of charging current, for example due to the failure of the thyristors SCR to turn off. Modified control circuits are described in which an analogue measurement of the cell voltage is made by charging a capacitor connected to the battery. The taper charge current may be controlled in dependence on a comparison of the battery voltage at two instants in a single interruption of the charge current.