Patent GB-190916273-A (GB)
Title: Improvements in Automatic Electric Switches.
Inventor: FERGUSON THOMAS
IPC: H02J7/14
Filed: 1909-07-13
Granted: 1910-07-07
Abstract: 16,273. Ferguson, T. July 13. Electro-magnetic switches.-Relates to automatic switches for connecting and disconnecting the dynamo in electric train lighting systems where storage batteries are used. The arrangement comprises a primary electro-magnetic switch actuated by a coil across the dynamo terminals, and a secondary electro-magnetic switch having a coil in series between the dynamo and battery, controlled by the primary switch and controlling the operating-coil of a main electro-magnetic switch, which is closed when the dynamo voltage rises a determined amount above the battery voltage and is opened when the dynamo voltage falls below the battery voltage. The two relays are in one modification combined together, forming an electro-magnet, with two separate armatures respectively carrying switch contacts. In another modification they are separate. In a third modification, referred to in the Provisional Specification only, the two relays are combined into one instrument with the main switch controlled by them. According to the first modification, Fig. 1, the dynamo a on attaining a certain voltage excites a coil c sufficiently to attract an armature e and make a contact at h. The other armature f is meanwhile, owing to the adjustments of the apparatus, left unmoved. The closing of the circuit at h allows current from the dynamo and battery in series to pass through a fixed coil u surrounding the armature f. The additional attraction thus produced, if the current is in the proper direction, moves the armaturef and completes a circuit at j through a coil v, which effects the main switching-in by raising a bridge-piece h<1> and putting it across the contacts e', g<1>. The dynamo is then charging the battery, and through switches q<1>, r', feeding the lamps. A coil t in the charging-circuit holds on the armature f, the coil u being short-circuited when the main switch closes. If the dynamo voltage falls below the battery voltage, the current through the coil t will be reversed and the armature f and e will be withdrawn by their springs s<1>, q, opening the circuit of the coil v and allowing the main switch to drop to the position across the contacts o' and p<1> ; this action leaves the lamps in circuit with the battery alone, through a flexible connector n'. Circuit connexions are shown for two groups of lamps L', L<2>. Resistances t<1>, u<1> are thrown in when the lamps are switched on, by the switch v, from the battery to the dynamo, and are cut out when the reverse operation takes place. To prevent the lights from blinking, the change is made in two steps by means of an additional electro-magnetic switch z<1> acting to keep part of the resistance short-circuited across the contacts w, x<1> until the dynamo has nearly reached its full voltage. In the second modification of automatic switch, Fig. 2, two separate electro-magnets l<1>, m<1> replace the electro-magnet c of the first modification, for the purpose of preventing the continued attraction of the armature e, in cases of a large drop of dynamo voltage, by the magnetic field due to the coil u. In the third modification, described in the Provisional Specification only, the main switch contacts are ca,rried by a plunger passing through one extending pole of an electro-magnet and adapted to move to or from the other pole. The electro-magnet and plunger are wound like the electro-magnet and armature f, Fig. 1, and there is a subsidiary armature acting like the armature e. The action is similar to that of the first modification.