GB952330A - Thermally-responsive electrical switch means - Google Patents

Abstract

952,330. Thermal switches; control of A.C. motors; protective arrangements. TEXAS INSTRUMENTS Inc. March 31, 1960 [March 31, 1959], No. 11424/60. Headings H2B, H2J and H2K. Thermal switches.-A thermal switch 46 comprises a cup-shaped metal casing 58 enclosing a similar insulating member 62, the space between their bases housing a bi-metallic disc 48 whose edge lies between members 58, 62 and whose centre engages an insulating transfer pin 50 having a portion 66 loosely fitted in an aperture 68 in a resilient upwardly-biased contact arm 70 co-operating with a fixed contact 78,terminals 54, 56 being bonded by glass portions 84 to a cover 82 which is sealed to the casing 58. The latter has an insulating layer 92 upon part of which is wound a heating coil 36 connected in series with the windings of an electric motor. Heating of the coil 36 due to a fault in the motor causes the disc 48 to snap upwards and allow the arm 70 to open the contacts, thereby disconnecting the motor and the coil 36 from the supply. Subsequent cooling of the disc 48 causes it to snap back to reclose the contacts. In a modification, Figs. 5 and 6 (not shown), three heating coils are wound on the outside of the switch, each coil being in series with one phase of a three phase motor. Figs. 8 and 10 show a further modification in which the thermostatic disc 174 carries current and is in series with the heating coil 172 and the windings of a split-phase motor. Terminals 164, 170 have straps 200, 202 which are secured to studs 196, 198 carrying fixed contacts 204, 206 and mounted on an insulating cup 194, to which the centre of the bi-metal disc 174 is secured by a threaded post 208. The contact-carrying parts of the disc 174 have ears 221, 223 guided in grooves 225, 227 in the cup 194. Heating or cooling of the disc 174 causes opening or closing of the contacts. Figs. 14 and 15 show a switch having a current-carrying bi-metal disc 312 and three internal heaters 266, 268, 270 each connected in series with one phase of a three-phase motor, heaters 266, 268 also being in series with external heaters 252, 258 respectively. The disc 312 is centrally supported on an insulating cup 294 by a threaded post 308 and carries contacts 273, 275, 277 adjacent which the disc has ears 322 guided in recesses 324 in the cup 294. The contacts 273, 275, 277 co-operate with fixed contacts 272, 274, 276 formed from members 302, 304, 306 secured in recesses 301, 303, 305 in the cup 294, the latter also having similar but vertically-displaced recesses 295, 297, 299 which house conductors 296, 298, 300 connected at their upper ends to terminals 248, 256, 262, and at their lower ends to contacts 272, 274, 276 through the heaters 266, 268, 270. The external heaters may comprise insulated foil or wire, the insulating layers 92, 224, 330 may be omitted and the current-carrying thermostatic discs 174, 312 may have sufficient resistance to cause self-heating. Control of A.C. motors; protective arrangements.-A single phase motor 43 driving the pump 100 of a refrigerator compressor unit is protected against overload by a thermal switch 46 whose heater 36 actuates a bi-metal element 48 controlling a switch 52 in the operating coil circuit of a relay 26. The heater 36 is wound on the outside of the casing of switch 46 which, with the motor 43, is mounted in the path of the refrigerant flow so that the thermal element and the motor windings heat and cool at rates proportional to each other under all conditions. The motor 43 comprises a start winding 42 and main winding 40 (displacement of the phase angle therebetween being effected in any known manner) and the switch 46 may be mounted against or near to these windings. Modifications include connecting the heater 36 to carry only the running winding current, and locating the start winding switch 44 outside the housing 102. A three-phase motor may be protected by a thermal switch having three heater windings each connected in series with a motor winding, Fig. 5 (not shown). If desired, one heater winding may be omitted. The arrangement of Fig. 1 may be modified so that the thermal element 48 forms the moving contact of the switch which is connected in series with the heater winding, Fig. 7 (not shown). Fig. 11 shows an arrangement in which the windings 254, 260, 264 of a motor 331 are in series with heaters 266, 268, 270 mounted inside the thermal switch 250, which has two external heaters 252, 258 and whose thermal element 312 acts as a switch.