GB1249729A - A thermal switch for an electrical circuit - Google Patents

Abstract

1,249,729. Automatic circuit breakers; thermal switches. ELLENBERGER &- POENSGEN G.m.b.H. 29 Oct., 1969 [7 Nov., 1968], No. 53074/69. Heading H1N. A thermal switch for an electric circuit comprises a bimetal strip 25 secured to one end of a heat storage device in the form of a block 27 with a heating element 30 secured to the other end of block 27 and a switch member 9 actuatable in dependence on bimetal strip 25 and a bimetal strip 37 heated by current passing through element 30 and carrying a movable contact 39 co-operating with a fixed contact 40 such that in the cold state of bimetal 37 contacts 39, 40 are closed and in the heated state contacts 39, 40 open to break the current to bimetal 37 and element 30. As shown, there are two separate electric circuits in the switch, (a) a main circuit comprising terminal 3, fixed contact 7, movable contact 8, bridge 9, fixed contact 10 which also serves as a latch, and terminal 4; and (b) an excitation circuit comprising terminal 5, heating coil 30, metal bar 28, bimetal 37, movable contact 39, fixed contact 40 and terminal 6. Heat from coil 30 on insulation 29 heats metal bar 28 which heats heat storage device 27 comprising a metal block for example constructed of copper-plated and nickel-plated iron which after a time delay heats bimetal 25 which bears on insulation 24 bearing on terminal 4. Bimetal 25 bends counter-clockwise and is followed by terminal 4, which is a pre-stressed spring, and latching block 10 frees bridge 9 which is moved upwards by spring 13 and spring 20. If pushbutton 11 is held down during this operation, bridge 9 will still move upwards under the action of spring 20. On cooling, bimetal 25 bends clockwise restoring terminal 4 . and block 10 and when pushbutton 11 is depressed, member 21 on member 15 on rod 12 integral with or attached to pushbutton 11 engages projection 22 on bridge 9 pushing bridge 9 down until it engages beneath block 10, release of pushbutton 11 allowing spring 20 to pivot bridge 9 about pivot 16 on member 15 so that projection 22 slides off member 21 re-engaging contacts 7, 8 with a quick action. If the excitation voltage is high bimetal 37 operates to keep making and breaking contacts 39, 40 to ensure that the heating up of bimetal 25 and the time lag remains constant with different excitation voltages. The excitation energy may be adjusted by adjusting screw 41. The tripping current strength of the switch is adjusted by screw 33 against spring 38, pivoting block 27 about a pivot 27<SP>1</SP>. In place of screw 33 ambient temperature compensating bimetal may be provided, Figs 3, 4 (not shown) bearing on metal bar 28 and openings are provided in the housing adjacent the compensating bimetal. The switch parts are held in recesses by the assembled housing parts secured by hollow rivets through holes 2. The switch may be plugged into a support by terminals 3, 4, 5, 6.