Patent GB-191501093-A (GB)
Title: Improvements in or connected with the Regulation or Control of Electric Currents.
IPC: H02J7/00
Filed: 1915-01-22
Abstract: 1093. Stone & Co., J., and Darker, A. H. Jan. 22. Electro-magnetic switches; sparking, preventing.-In an electromagnetically-operated switch of the type used to control the charging of batteries, especially batteries in a train lighting or heating system, the armature or core, when attracted to effect a switching movement, opens another air-gap of such dimensions that the reluctance to magnetization of the magnetic circuit is only slightly changed, whereby the electro-magnet releases its armature and allows the switch to open at about the same number of ampere-turns as when attraction took place. In the construction shown in Fig. 1, a fixed pole-piece b with a tapered depression m extends into the interior of the magnet frame f and co-operates with the conical-ended movable core a, which has a reduced part passing through an aperture n in the frame, the part of full diameter normally resting, with a clearance, within the aperture, upon a brass sleeve g adjustable within a brass bushing h screwed into the aperture. The lower end of the movable core carries a brush contact p guided to move rectilinearly by the pin 9 and slot 8 and cooperating with the contacts q, r, and an auxiliary sparking-contact s co-operating with the contact t. The shunt winding c of the electromagnet, which causes the initial attraction of the core a, is connected across the terminals of the dynamo, and the series winding d is connected up when the core is attracted and the contact p closed, and co-operates in holding up the core. When the core is sucked up, the airgap between the conical-shaped ends of the two cores is reduced, but at the same time, the airgap in the aperture n is increased to almost the same extent. The upward movement of the core a raises an adjustable rod u located in the hollow core b, lifts an adjustable spring brush w from the contact y, and, as shown, opens the short-circuit of a resistance 5 in the lamp circuit. If a certain maximum current is exceeded in the series winding, the right-hand side of the brush p, which is in contact with the contact r, is strained so that the shorter left-hand side of the brush engages with the contact q, and consequently the resistance 2 is inserted in parallel with the series winding. In a modified construction for introducing a resistance in parallel with the series winding, two two-armed brushes are employed, the first of which closes the series winding and closes the circuit of the shunt resistance through a high resistance, and the second of which, operated with excessive current, short-circuits the high resistance. When the second brush breaks contact, the circuit is not completely broken by reason of the high resistance, and consequently sparking is prevented. In the application, shown in Fig. 3, to a pivoted armature 17 carrying a brush 20, the reduction in the air-gap between the pole 16 and the armature is accompanied by an increase in the air-gap at the pivot, the bearings 18 of which may be of non-magnetic material. The series circuit is completed by the engagement of the contacts 20, 21, and the adjustable stop 27 at the same time raises the contact member 23 from the contact 21 to the contact 24.