Mechanical Reversal of the Current

Magnets and Currents:
The Commutator. It is not possible by hand to reverse the current with sufficient rapidity and precision to insure uninterrupted rotation; moreover, the physical exertion of such frequent reversals is considerable. Hence, some mechanical device for periodically reversing the current is necessary, if the motor is to be of commercial value.

The mechanical reversal of the current is accomplished by the use of the commutator, which is a metal ring split into halves, well insulated from each other and from the shaft. To each half of this ring is attached one of the ends of the armature wire. The brushes which carry the current are set on opposite sides of the ring and do not rotate. As armature, commutator, and shaft rotate, the brushes connect first with one segment of the commutator and then with the other. Since the circuit is arranged so that the current always enters the commutator through the brush B, the flow of the current into the coil is always through the segment in contact with B; but the segment in contact with B changes at every half turn of the coil, and hence the direction of the current through the coil changes periodically. As a result the coil rotates continuously, and produces motion so long as current is supplied from without.

FIG. - The commutator.