Fig. 18. Diagram of K6 Controller Combinations.
From these diagrams it is seen that the motors are first operated in series until all the resistance is short-circuited by the controller. When this has occurred, the cars are running at about half speed. The next point on the controller puts the two motors in multiple, with some resistance in the circuit, which resistance is cut out upon the following points, until at full speed the two motors are in multiple, without any resistance in the circuit.
Fig. 19. Motor in Series.
Four Motors. Where four motors are used on a car, as is frequently the case with double-truck cars, the motors on each truck are usually controlled just as in case of the two-motor equipment that has been described; but each pair of motors is operated in multiple. That is, on the first points of the controller, the two motors of a pair are in series, as in [Fig. 19], and the two pairs are in parallel; and on the last points of the controller, all the motors are in parallel, as in [Fig. 20].
Fig. 20. Motor in Parallel.
Controller Construction. The controller (Type K) shown open in [Fig. 21], which in its various forms is the type most commonly used on street cars in the United States, has a contact cylinder or drum mounted upon the main shaft of the controller. This contact drum carries contact rings insulated from the drum, and is suitably interconnected, as indicated in [Fig. 22], which shows the contact rings of the controller as they would appear if rolled out flat. Contact fingers are placed along the left side of the controller, as seen in [Fig. 21], one for each ring on the drum; and as the controller handle is turned to revolve this drum, the contact fingers make contact with the rings on the drum and give the various connections. Alongside the main controller drum is a reverse drum which simply reverses the armature connections of the two motors. Controller Wiring. The connection between motors, controllers, and resistances, with two motors and a K6 controller is shown in [Fig. 22]. A careful study of this will show the combinations to be the same as indicated in the diagram, [Fig. 18]. The wiring is rather complicated; and in practice, to avoid confusion, the ends of each wire are labeled with tags showing the terminals to which they belong.
