GB307718A - Improvements in and connected with thermostatic controls for dynamo electric machines - Google Patents

Abstract

307,718. Stone & Co., Ltd., J., and Darker, A. H. Dec. 6, 1927. Regulation, automatic. - A dynamo-electric machine which supplies the current for a railway vehicle heating system or which operates the compressor of a refrigerator is controlled by means of a heat-sensitive element which completes a lowvoltage circuit of a relay which controls the circuit of an electromagnetic switch which controls the dynamo-electric machine. An axledriven dynamo d, Fig. 1, is connected by positive and negative leads a, b to heaters h and to a fan f for circulating the air. A mercury column thermostat t is connected to the coil r of an electromagnet switch having a potential difference of about 1 volt derived from a potentiometer p across the mains. The switch contact r<2> is connected to the terminal s<1> of the solenoid coil s, the other end of which, s<2>, is connected through a hand switch m to the positive main a. The field winding of the dynamo is connected by a wire e to a terminal o and thence through resistance p<1> and terminal S<SP>2> to the main a. The resistance p<1> is shunted by a coil p<2> wound non- inductively with the coil s, and its effective resistance is varied by making the resistance p<1> an interchangeable unit. The contact member q carried by the armature is connected by wire q<1> to terminal s<2>, and normally rests on contact q<2>, so that the resistances p', p<2> in series with the dynamo field winding are short circuited, and the maximum current supply is available for the field windings. If the thermostat makes contact at t<2>, the relay operates to raise the contact member q, insert the resistance p', p<2> in the field windings, and thereby reduce the dynamo excitation and supply of current to the heaters h. The position of the contact t<2> is adjustable to vary the temperature control point. In the application to a refrigerator control, Fig. 3 (not shown), the compressor is driven by a series-wound motor supplied by an axle driven dynamo, and the field winding of the motor is paralleled by a variable resistance in series with The non-inductive resistance on the solenoid. The non-inductive resistance is normally short-circuited, but the short-circuit is broken by the relay at the predetermined temperature, thus increasing the resistance in parallel with the motor field winding and increasing the current in the field windings. In another modification, applicable to a shunt-wound motor, Fig. 4 (not shown) the shunt winding of the motor is in series with a variable resistance which is normally short-circuited, but is placed in the circuit by the relay switch at a predetermined temperature. The thermostatic device may have more than two contacts, and an embodiment of this device is described in Fig. 5, not shown.