Fig. 239.
165. The Controllers, as the name suggests, control the speed of the car by allowing more or less current to pass through the motors. The motors, resistance coils and controllers are so connected with each other that the amount of current used can be regulated.
Fig. 240.
When the motorman turns the handle of the controller to the first notch, the current passes through all of the resistance wires placed under the car, then through one motor after the other. The motors being joined in series by the proper connections at the controller, the greatest resistance is offered to the current and the car runs at the slowest speed at this first notch. As more resistance is cut out by turning the handle to other notches, the car increases its speed; but as the resistance wires become heated and the heat passes into the air, there is a loss of energy. It is not economical to run a car at such a speed that energy is wasted as heat. As soon as the resistance is all cut out, the current simply passes through the motors joined in series. This gives a fairly slow speed and one that is economical because all the current tends to produce motion.
By allowing the current to pass through the motors joined in parallel, that is, by allowing each to take a part of the current, the resistance is greatly reduced, and a higher speed attained. This is not instantly done, however, as too much strain would be put upon the motors. As soon as the next notch is reached, the motors are joined in parallel and the resistance also thrown in again. By turning the handle still more, resistance is gradually cut out, and the highest speed produced when the current passes only through the motors in parallel.
Fig. 241.
