Patent GB-190602716-A (GB)
Title: Improvements in or relating to Automatic Starting Devices for Electric Motors.
Inventor: BOULT ALFRED JULIUS
Filed: 1906-02-03
Granted: 1906-11-01
Abstract: 2716. Boult, A. J., [O'Brien, W. C.]. Feb. 3. Switches. - One or more solenoids in series with the armature winding of a direct-current electric motor allow their cores to drop, and so to cut out starting- resistance, at a rate corresponding to the falling off of the current. In the simplest form, shown in Fig. 1, and suitable for small motors for machine tools &c., where only one resistance step R is utilized, the line current from constant - potential mains L, L', turned on by a switch S, flows initially through an electro-magnet H in series with the solenoid C, the starting - resistance R, and the motor armature a, the field winding of which is connected across the mains. The hinged armature of the electro-magnet H is then pulled up to meet a contact and short-circuit the resistance R, but, should the current exceed the normal, the cord 10 rises, simultaneously separating the contacts 11, 8, and preventing the short-circuit from being formed. If desired, the core is made with an extension 15, and itself acts to lift the arm of the electro-magnet H. When the current afterwards diminishes upon the speeding - up of the motor, the core falls, leaving the arm held-on, and cuts out the resistance. In a more elaborate arrangement, shown in Fig. 4, a number of solenoids C<1>, C<2>, C<3>, C<4>, having corresponding resistances R<1>, R<2>, B<3>, R<4>, and each acting in the same manner as the single one in Fig. 1, are placed in series with the motor armature. By means of differently-weighted cores, or otherwise, they are made responsive to currents of different strength; and their short-circuiting contacts 14<a> . . . 14<d> are placed so as to be simultaneously met by a bar 13 lifted by a shunt or series solenoid H<1> responsive to any working current and with a core partly counterbalanced by springs 20. One or more of the cores of the solenoids C' ... C<4> rises simultaneously, thus keeping a corresponding amount of starting-resistance in the circuit of the motor armature, and then afterwards fall in regular order as the current diminishes. In another arrangement, Fig. 6, a solenoid C, initially in series with the whole of the subdivided resistance R<8> and with the motor armature a, first lifts a rheostat arm 71, against gravity and an adjustable spring 82, to the position shown in dotted lines, where the arm meets a clip contact 76 and forms a branch path for the current, also including the full resistance R<8>. The end 75 is hinged at 72 to the rest of the arm, and is held down by an electro-magnet H<2> while the solenoid C, under diminishing current, lets the arm 71 fall and cut out resistance step by step. In a modified form, Fig. 8, the solenoid has an additional fine winding c<2>, fed by a shunt between the terminals 51, 52, the source of which is through the contacts 88, 89 and a bridging- contact 92 on the end of the arm 75. On the switch S being closed, current passes only through the winding c<2> and the hold-on magnet H<2>. The shunt is broken when the core reaches its full height, and circuit is made through the arm 71, the full resistance R<9>, and the main solenoid coil c<1> to the motor armature. Subsequent cutting out of resistance proceeds as before. A cross-connexion 93 causes the solenoid to be short-circuited when all resistance is cut out.