DYNAMO 



1894 



DYNAMO 



so that it can be rotated we shall secure two 

 reversals of the current in the wire at each ro- 

 tation (Fig. 2). If the ends of this wire are 

 connected by leaders to a galvanometer (which 

 see), this instrument will show that the strength 



\ 



\ 



FIG. 2 



of the current increases with the rapidity of 

 rotation. Now the dynamo is constructed on 

 this principle. An electro-magnet is used in 

 place of a steel magnet because it can be made 

 so much more powerful. 



A Simple Dynamo. Fig. 3 shows a simple 

 dynamo, and one that any ingenious boy can 

 make with a few tools and the aid of a black- 

 smith. The part e is the electro-magnet, on 

 which n and s represent the + and poles; 

 / is a rotating disk to which two other magnets 

 are attached. This is mounted on the shaft h, 

 which is belted from the pulley to a drive 

 wheel. Two brushes, a and b, are connected 

 with the two insulated copper strips, r r, and 

 with the coils of e by the wires I, m. 



Iron always possesses some magnetism, which 

 is produced by the work done upon it in pre- 

 paring it for use. Each magnet generates a cur- 

 rent in the other. At first this current is very 

 feeble, but it rapidly gains strength with the 

 rotation of the revolving magnet. At each 

 half revolution of the shaft the relative posi- 

 tions of these insulated copper strips are re- 

 versed, and at the same time the currents 

 generated in the revolving magnet are re- 

 versed. They pass out by the brush b and re- 

 turn through a, circulating in this direction 

 through the external circuit and coils of the 

 magnet e, as shown by the arrows. The cur- 

 rent generated in the revolving magnet is a 

 broken and reversed current, and for this reason 

 is called an alternating current, but it is 

 changed to a direct or continuous current in 



the coils and external circuit of the permanent 

 magnet. 



Parts. The revolving magnet is the arma- 

 ture, the stationary magnet is the magnetic 

 field, and the insulated pieces of copper form 

 the commutator, because by them the alter- 

 nating current is commuted, or changed, to a 

 direct current. 



The Commercial Dynamo. Dynamos are uni- 

 polar, bi-polar and multi-polar, according to 

 the number of magnets in their magnetic field. 

 Most of those in practical use are multi-polar, 

 and contain as many magnets as can be used. 

 The armature is usually a drum and revolves 

 within the field magnet. The commutator is 

 attached to the shaft of the armature, and 

 brushes connect with the main-line wires. 





FIG. 3 



Dynamos are of two general classes, alternat- 

 ing current and direct current, and there are 

 many different patterns in each class, but all 

 are based on the principle explained in the 



