The electrical circuit-connections are substantially the same as indicated in the previous diagrams, the solenoid being in series with the circuit when the translating devices are in series, and in shunt when the devices are in multiple arc. The operation of the device is as follows: When upon a decrease of the resistance of the circuit or for some other reason, the current is increased, the solenoid S gains in strength and pulls up the iron core I, thus shifting the main brushes in the direction of rotation and the auxiliary brushes in the opposite way. This diminishes the strength of the current until the opposing forces are balanced and the solenoid is traversed by the normal current; but if from any cause the current in the circuit is diminished, then the weight of the moving parts overcomes the pull of the solenoid, the iron core I descends, thus shifting the brushes the opposite way and increasing the current to the normal strength. The dash-pot connected to the iron core I may be of ordinary construction; but it is better, especially in machines for arc lights, to provide the piston of the dash-pot with a valve, as indicated in the diagrams. This valve permits a comparatively easy downward movement of the iron core, but checks its movement when it is drawn up by the solenoid. Such an arrangement has the advantage that a great number of lights may be put on without diminishing the light-power of the lamps in the circuit, as the brushes assume at once the proper position. When lights are cut out, the dash-pot acts to retard the movement; but if the current is considerably increased the solenoid gets abnormally strong and the brushes are shifted instantly. The regulator being properly adjusted, lights or other devices may be put on or out with scarcely any perceptible difference. It is obvious that instead of the dash-pot any other retarding device may be used.
CHAPTER XXXIX.
Improvement in the Construction of Dynamos and Motors.
This invention of Mr. Tesla is an improvement in the construction of dynamo or magneto electric machines or motors, consisting in a novel form of frame and field magnet which renders the machine more solid and compact as a structure, which requires fewer parts, and which involves less trouble and expense in its manufacture. It is applicable to generators and motors generally, not only to those which have independent circuits adapted for use in the Tesla alternating current system, but to other continuous or alternating current machines of the ordinary type generally used.
Fig. 268 shows the machine in side elevation. Fig. 269 is a vertical sectional view of the field magnets and frame and an end view of the armature; and Fig. 270 is a plan view of one of the parts of the frame and the armature, a portion of the latter being cut away.
The field magnets and frame are cast in two parts. These parts are identical in size and shape, and each consists of the solid plates or ends A B, from which project inwardly the cores C D and the side bars or bridge pieces, E F. The precise shape of these parts is largely a matter of choice—that is to say, each casting, as shown, forms an approximately rectangular frame; but it might obviously be more or less oval, round, or square, without departure from the invention. It is also desirable to reduce the width of the side bars, E F, at the center and to so proportion the parts that when the frame is put together the spaces between the pole pieces will be practically equal to the arcs which the surfaces of the poles occupy.
The bearings G for the armature shaft are cast in the side bars E F. The field coils are either wound on the pole pieces or on a form and then slipped on over the ends of the pole pieces. The lower part or casting is secured to the base after being finished off. The armature K on its shaft is then mounted in the bearings of the lower casting and the other part of the frame placed in position, dowel pins L or any other means being used to secure the two parts in proper position.
