GB1509825A - Motor-alternator with automatic start-stop control - Google Patents

Abstract

1509825 Control of D.C. motors APPLIED MOTORS Inc 12 April 1976 [17 April 1975] 14853/76 Heading H2J A motor-alternator set for supplying A.C. to a load 17 includes a control circuit for starting and stopping the motor 19, the control circuit comprising a current limiting resistor R6 and a diode D2 which are supplied with current from a battery 13 so that when a switch 16 is closed, the potential across the diode causes current to flow through a resistor R1 to energize a relay CR1 thereby connecting the motor 19 to the battery and the motor driving the alternator 20 to supply A.C. via diodes D1-D4 to the load. The load may be a transformer or a motor for drive a power tool. When the switch 16 is closed, the potential across the diode D2 causes a current to flow through the resistor R1 via the alternator 20, the switch 16 and the load 17. The potential across the resistor R1 switches on a transistor Q1 which is turn switches on transistors Q2, Q3 to connect the relay CR1 to the battery. Relay contacts CR1-a are therefore closed to connect the motor to the battery. The motor drives the alternator, the positive half cycles from which are conducted by the diodes D1, D4 whilst the negative half cycles are conducted by the diodes D2, D3. During the positive half cycles the voltage Vc across the resistor R1 rises to the sum of the voltage drops across the diodes D4, D1, D2 to switch on the transistor Q1 in each positive half cycle. During negative half cycles the polarity of the voltage Vc is reversed so that the transistor Q 1 is turned off. A capacitor C1 however holds the voltage across resistors R3, R4 during the negative half cycles to prevent the relay being de-energized. When the switch 16 is opened the voltage Vc falls to zero so that the relay is de-energized and the load supply is therefore cut off. If the load has a shunt capacitor, opening of the switch 16 may not switch off the motor 19. To prevent such malfunction, a large value capacitor may be connected across the diodes D2, D3. Alternatively the series combination of a resistor and a transistor may be connected in parallel with the resistor R1, the transistor being switched on to connect the series resistor in parallel with the resistor R1 when the switch 16 is opened to ensure that the motor is switched off.