GB818580A - Improvements relating to starter control devices for split-phase electric motors - Google Patents

Abstract

818,580. Control of A.C. motors; electromagnetic switches; thermal switches. GENERAL MOTORS CORPORATION. March 25, 1958 [April 8, 1957], No. 9537/58. Classes 38 (3) and 38 (5). A starting device for split-phase motors, enabling motors of different characteristics to be operated satisfactorily over a wide range of supply voltages, comprises an electromagnet having its coil 48 connected in series with the main winding 70 of the motor, a bar armature 56 mounted alongside the electromagnet by a spring hinge 54, and a contact-spring 58 adapted to close the circuit of the phase winding 68 of the motor. The spring 58 is biased to the closed position but is kept in the open position by the spring-force of the armature until the latter is attracted, the member 58 being joined to a, portion 78 of a bimetallic strip 24 which also has an extension 76 adapted to be deformed by the phase winding current and to apply to the member 58 a force which adds to the spring- force of the armature. This arrangement allows satisfactory operation, even at low voltages. The portion 78 is not substantially heated by current-flow but compensates for the effect of ambient temperature upon the extension 76. If the armature 56 is not released with a normal decrease in main winding current, the extension 76 continues to bow towards the right until the starting contacts 58, 62 are opened before the overload contacts 34, 40 are tripped. In a modification, the spring contact is formed of a single bimetallic strip 124 having offset portions 127, 131, and a movable contact 133 spring- ,biased to engage contact 62. The offset portions are electrically insulated from each other so that the phase winding current normally flows through the leg 129. If current-flow through this leg is prolonged, contact 133 is disengaged from contact 62 and the leg is bowed until it engages a stop.