Patent GB-1304839-A (GB)
Title: Improvements relating to automatic electric battery charging apparatus
Inventor: CLAYTON DENNIS ALBERT
IPC: H02J7/12
Filed: 1969-03-03
Abstract: 1304839 Automatic voltage control; automatic voltage and current regulation ELECTRIC POWER STORAGE Ltd 2 March 1970 [3 March 1969] 11160/69 Headings G3R and G3X [Also in Division H2] Battery charging apparatus comprises means to automatically adjust the charging current to bring the battery voltage while on charge to a datum value during at least a part of a charging cycle and means to progressively increase the datum value and thus cause the battery voltage to follow the increases of the datum value. The charging apparatus shown in Fig.1, provides three phases of operation as follows:- (1) a reference voltage representative of the datum value is increased uniformly at a predetermined rate to correspondingly increase the charging current and cause a signal voltage indicative of battery voltage to follow the reference voltage. (2) during the period of rapidly-rising battery voltage (corresponding to gassing) the signal voltage rises faster than the reference voltage and causes the charging current to be progressively reduced, the signal voltage again following the reference voltage. (3) when the battery voltage flattens out (corresponding to full charge) the signal voltage again lags the reference voltage and causes the charge to be terminated. Thereafter a boosting charge is commenced whenever the open circuit battery voltage falls below a predetermined value and is terminated when the battery voltage reaches the value of the reference voltage existing when the main charge was terminated. The reference voltage is provided by a potentiometer 40 driven by a motor 40/1 and the signal voltage is obtained from a potentiometer 50 driven by a motor 50/1, which is energized during an initial adjusting operation preceding the main charge so that the setting of potentiometer 50 is made equal to the setting of potentiometer 40. After this has been effected motor 50/1 is de-energized and the setting of potentiometer 50 remains unchanged for the charging phases described above. During phase (1) the difference between the reference and signal voltages energizes a relay 13 which controls a motor 33 for adjusting the tap position 32 of a transformer 22 to increase the charging current. The reference voltage is chosen so that the charging current is increased to its maximum value in a predetermined time, at which value it remains for the duration of phase (1). However if the battery is not fully discharged the signal voltage rises sufficiently rapidly to prevent this value being reached. During phase (2) the difference between the reference and signal voltages energizes a relay 25 which controls a motor 34 for adjusting the tap 32 to decrease the charging current. The reference motor 40/1 remains energized during these adjustments, in contrast to the phase (1) operation when it is de-energized during the periods of energization of relay 13. At the commencement of phase (2) energization of the relay 25 energizes a selfholding memory relay 26 through contacts 25/2, 20/2 of which the latter are controlled by a relay 20 energized by conduction of transistors 18, 19 at the start of phase (1). Thus at the commencement of phase (3) the energisation of the relay 13 causes a self holding relay 27 to be energized, whose contacts 27/2 remove the supply to motors 40/1, 33, 34 and whose contacts 27/3 deenergize the relay 20 to remove the A. C. supply from transformer 22 and so terminate the charge. In addition the relay contacts 20/3 open to adjust the divider 17, 30 and so reduce the operating voltage setting of transistor 18 to a predetermined open circuit voltage of the battery. When this is reached the relay 20 is again energized and charging current flows at a value corresponding to the setting of tap 32 at the end of phase (2). When the signal voltage of potentiometer 50 exceeds the reference voltage, relay 25 is energized to de-energize relays 20, 21 and so terminate the boosting charge. If the battery is disconnected whilst on charge, the transistors 18, 19 cut off to remove the A.C. supply to transformer 22, all relays are released and members 32, 40, 50 return to their original pre-charge positions. A similar operation occurs if the A. C. supply is interrupted during charge. The instigation of a complete re-charge sequence after such faults may be avoided by connecting the motor and tap change clutches 40/2, 50/2, 31 across the Zener diode 64. Potentiometer 50 may be adjusted manually before charge, phase (1) may be replaced by manual selection of a desired charging current and the phase (3) boosting charge may be omitted or replaced by a timed charge. The charging apparatus shown in Fig.2 omits the potentiometer 50, replaces the potentiometer 40 by a capacitor 105 which is steadily charged to provide the rising reference voltage and replaces the tapped transformer by a transformer 77 controlled by a saturable reactor 78. When the A.C. supply is switched on (switches 73 closed, relay 74 energized and contacts 74/1 close), the capacitor voltage is zero so that the current in the reactor control winding 91 (controlled by  transistors 89, 107, 108, 109) is low to produce a low charging current. As capacitor 105 charges up the charging current is correspondingly increased up to a designed maximum value. The circuit design is also such that stabilization occurs at a predetermined rate of rise of battery voltage, at which the currents through transistor 107 and resistor 106 are constant to produce a constant charging current. Variation about this rate of rise (due to variation of the charging current) varies the capacitor charging current and hence the current in winding 91 to restore the charging current and rate of rise to their original values. When the A. C. supply is switched on current flows through a differentiating circuit 95, 96, 97 to energize a relay 99 through transistor 98 and prevent energization of a memory relay 102, the circuit design being such that relay 99 stays energized until the battery voltage rises more steeply due to the onset of the gassing condition. As a result the relay 102 is energized in selfholding manner and its contact 102/3 opens. During the period of rapid rise in battery voltage the current in winding 91 is progressively reduced to correspondingly reduce the charging current, until the full charge condition and its reduced rate of rise are reached. Accordingly the current in winding 91 and the charging current again start to increase, the former condition re-energizing the relay 99 to open its contacts 99/3, de-energize relay 74 and so break the A. C. supply to the transformer 77. Member 74/3 and/or member 111 discharge(s) capacitor 105 ready for the next charging operation. The tapped transformer and saturable reactor of Figs. 1 and 2 may be interchanged or replaced by a thyristor-controlled pulsing circuit.