THE DYNAMO. 7 1 



The motor and generator of a motor-generator set may be 

 built as one machine, that is, a machine having one field magnet 

 and one armature structure but with two distinct windings, one 

 of many turns of fine wire connected to a commutator at one end, 

 and another of fewer turns of coarse wire connected to a second 

 commutator at the other end. This machine can then be run as 

 a motor by a small current delivered to its fine wire windings 

 from the supply mains, and at the same time it will operate as 

 a generator and deliver a large current at a reduced voltage from 

 its coarse wire windings. Such a machine is called a dynarnotor. 

 Fig. 6 1 shows a dynamotor made by the Crocker- Wheeler Corn- 



Fig. 61. 



pany and designed to take current from I lo-volt mains and to 

 deliver current from its coarse wire armature winding at 25 volts. 



40. The homopolar dynamo. A simple type of direct-current 

 dynamo, hitherto but little used on account of its very low elec- 

 tromotive force, is the so-called homopolar dynamo (sometimes 

 called the unipolar dynamo, and sometimes the acyclic dynamo). 

 Fig. 62 shows a longitudinal section and an end view of a 

 simple type of homopolar dynamo. 



The armature is a solid cylindrical piece of soft iron or steel 

 A A which rotates inside of a hollow cylindrical field yoke YY. 



