GB1485823A - Battery charges - Google Patents

Abstract

1485823 Charging batteries; controlling rectifiers; protecting against overcurrent WALTER KIDDE & CO Ltd 2 June 1975 [19 April 1974] 17369/74 Headings H2H H2F and H2K A battery charger comprises a bridge rectifier for converting A.C. to D.C. to charge a battery B, the bridge rectifier including thyristors CSR1, CSR2, transistors TR1, TR2 for detecting the state of charge of the battery and trigger circuits responsive to the conduction of the transistors for varying the power supplied by the bridge in accordance with the state of charge of the battery. Each trigger circuit includes the collector-emitter path of the respective transistor TR1, TR2, a diode D3, D4 and a resistor capacitor network R1, R2, C1 or R3, R4, C2. When the battery voltage is low the transistors are fully conductive so that the thyristors are fired early in each half-cycle and the battery is charged at a high rate. As the battery voltage increases the conduction of the transistors decreases so that the thyristors are fired later in each half-cycle to reduce and finally cut-off the charging current. The rectifier provides a smoothed, unregulated output on a bus-bar 1 for loads such as alarms, ventilation shut down equipment or automatic door closing equipment and a regulated supply on a bus-bar 2 for control equipment such as ionization fire detectors. The regulator circuit includes an overload detecting relay RL2, the contacts RL2.1, RL2.2 of which open when an overload current due to a short circuit exists, to switch off a thyristor CSR3. A transistor TR3 is therefore turned off so that base bias is not supplied to transistors TR4-TR23. The regulated supply on the bus-bar 2 is therefore switched off. The supply is restored by depressing a reset switch SW1 to trigger the thyristor CSR3 and switch on the transistor TR3. A relay RL1 with bifilar windings responsive to the A.C. supply and the battery voltage respectively operates contacts RL1.1 to sound a bell, buzzer or flashing light if the battery or mains fails. The thyristors may be light activated.