GB474149A - Improvements in or relating to electric motor controllers - Google Patents

Abstract

474,149. Control of A.C. motors ; thermal switches; snap-action switches. IGRANIC ELECTRIC CO., Ltd. May 6, 1937, No. 12943. Convention date, May 11, 1936. [Classes 38 (iii) and 38 (v)] A motor controller comprises a starting switch 1 for controlling starting connections of a motor M, a running switch 2 for controlling power connections of the motor, and thermal means heated in accordance with the current taken by the motor for controlling both switches. In the construction shown, each switch comprises a pair of U-shaped levers 7, 8 arranged in opposed relation on opposite sides of a supporting bracket 9 in a casing 3. The side arms of the levers are formed with knife edges engaging V-shaped recesses in the associated brackets 9, the free ends of the levers being connected together by a spring 13. The free ends of the levers 7 carry contacts 7b co-operating with stationary contacts 11, 12, the switches being normally in the closed position. The switches are provided with thermally-responsive operating elements 4, 5 under the control of an electric heater 6 connected between terminals 14, 15. Each of the elements 4, 5 comprises an elongated bimetallic strip fixed at one end to a terminal 16 or 17 and carrying at its free end an insulating plate 18, the insulating plates being recessed to receive the free ends of the levers 8. The operating element 4 carries an auxiliary heater 21 in the form of an insulated resistance wire connected at its lower end to the element 4 and at its upper end to the terminal 14. The device is connected as shown in Fig. 4 to control a splitphase A.C. motor M having a main winding 27 and a starting winding 28 connected 'in series with a condenser 29. On closing a line switch 25, both windings are energized, and current passes through the heating-coils 21, 6. The coil 21 provides for rapid heating of the element 4, and after a predetermined interval, the said element moves the lever 8 to the left until the spring 13 passes over the dead-centre, when the switch 1 opens with a snap action, and the starting winding is disconnected. The auxiliary heater 21 is then de-energized, but the heater 6 maintains the element 4 sufficiently heated to keep the switch 1 in the open position. The switch 2 remains closed under normal current conditions in the motor circuit, but opens on predetermined overload conditions. When this happens, the heater 6 is de-energized and both operating elements 4, 5 cool and return to normal position to reclose the switches 1 2 with a snap action, the switches being so adjusted that the switch 1 closes first. The switches may be adjusted by eccentric cams 30 engaging the elements 4, 5 and by adjustable stops 32 which cooperate with the levers 7. The casing 3 is provided with a terminal compartment 33 having wiring openings 34. In a modification, the auxiliary heating coil 21 is dispensed with.