GB582031A - Improvements in controllers for electric motors - Google Patents

Abstract

582,031. Control of A.C. motors; magnetic control of switches. CONSTANTINE, W. W. (General Motors Corporation). June 23, 1944, No. 11928. [Classes 38 (iii) and 38 (v)] A controller for electric motors having starting and running windings comprises a thermallyresponsive switch which in one position places the starting winding in circuit and which when heated moves to disconnect the starting winding and is thereafter movable between two further positions in one of which the current heating is effective and in the other is eliminated. Control means for an electric motor 20 having a main winding 22 and a starting winding 24 comprise a bimetallic strip 44, which is the actuating element of the overload control, a bimetallic strip 60 for starting control, and two heaters 36 and 56. Another heater, mounted similarly to the heater 56 may be placed adjacent to the bimetallic strip 60. When power is supplied to the motor at standstill current flows through the heater 36, both sides of the strip 44, the heater 56, one side of the. strip . 60 through the starting winding, and through a pigtail connection 84 to the running winding. The bimetal 60, being actuated before the strip 44, causes contact 70 to engage a contact 76 and shunt the bimetal 60 and heater 56 and remove the starting winding from circuit. The bimetal 60 and heater 56 cools and the strip takes up an intermediate position between the contacts 76 and 78 where it is again heated and re-closes with the contact 76. This alternate heating and cooling of the strip 60 and the heater 56 affords means for keeping a substantially steady temperature within the controller casing. The control may be applied to a split phase motor as shown in Fig. 1, or a capacitor start type of split phase motor, or a capacitor start and run motor. The overload bimetallic strip 44 has a sufficient heat storage capacity and large differential so that when it trips it will remain open a sufficient length of time to allow the starting control to return to the starting position. Mechanical means may be used to throw the starting bi-metallic strip to the starting position when the overload control moves to the open circuit position. In further embodiments of the invention, a permanent magnet is provided to afford a snap action and to ensure that when the starting and overload controls trip open they will re-set simultaneously.