Fig. 282.—Diagram showing current distribution through armature of a four pole machine with like brushes connected. There are four paths in parallel, hence the induced voltage will equal that of one set of coils, and the current will be four times that flowing in one set of coils.
Ques. How are the brushes connected?
Ans. Usually all the positive brushes are connected together, and all the negative brushes as in [fig. 283], giving four paths in parallel through the armature as indicated in [fig. 282].
Fig. 283.—Brush connections for four pole dynamo. It is usual to connect all the positive brushes to one terminal and all the negative brushes to the other which gives four parallel paths as shown in the diagram, [fig. 282]. In a four pole machine, two separate currents can be obtained by omitting the parallel brush connections.
Ques. How does this method of brush connection affect the voltage?
Ans. The voltage at the terminals is equal to that of any of the sets of coils between one positive brush and the adjacent negative brush.
Thus in the four pole machine, [fig. 283], the coils of the four quadrants are in four parallels, which gives an internal resistance equal to one-sixteenth that of the total resistance of the entire ring.
When the coils are connected in two circuits or series parallel, it requires only two brushes at two neutral points on the commutator, for any number of poles; this arrangement is shown in [fig. 269].
Ques. In general what may be said about the current paths through an armature?