THE DYNAMO. 



53 



Fig. 40. 



Fig. 39 is used chiefly in large alternators in which the field 

 magnet rotates inside of a large stationary ring-shaped armature. 



Fig. 40 is a general 

 view of an early type of 

 bipolar dynamo manu- 

 factured by the Crocker- 

 Wheeler Company. The 

 base plate of the machine 

 serves as the field yoke, 

 and the bearing pedestals 

 and base plate are cast in 

 one piece. Each field 

 magnet core and pole 

 piece is forged from a 

 single piece of wrought 

 iron,* and the two 

 pole pieces are connected at the top by a non -magnetic brass 

 plate which serves as a protective cover for the armature. 

 The armature is of the ring type, the windings of which are 

 concentrated in a number of coils which lie in deep slots on 

 the outside surface of the armature as shown in Fig. 41. The 

 armature core is, of course, built up of sheet iron stampings, and 

 in order to facilitate the winding of the armature coils, the two 

 halves (right and left as seen in Fig. 41) of the armature core 

 are built up separately and put together after the coils are wound 

 upon them. The two halves of the armature core are held 

 together by small bolts BB which pass through the interleaved 

 stampings of the two halves of the core. The armature core is 

 supported by small bolts like BB which pass through the 

 armature teeth and connect to two end plates of brass which are 

 attached to the shaft. The brass plate at the commutator end is 

 provided with apertures through which the commutator leads 



* A more usual construction is that in which the field magnet cores are wrought 

 iron or cast steel, and the pole pieces are separate pieces of cast iron or cast steel bolted 

 to the ends of the cores. 



