Sunday, December 1, 2013

Reversing DC Motors

Procedure for reversing direct current motors

Direct current motors are reversed by changing the direction of current flow through the armature or through the field. In series motors, the usual procedure is to reverse the current through the armature. Figure 1 shows this method.

All that is necessary is to interchange the leads on the brush holders. Figure 2 shows the series motor reversed by changing the current in the field circuits.


Reversing of a two-pole series motor by interchanging armature leads
Figure 1: Reversing of a two-pole series motor by interchanging armature leads
Reversing of a two-pole series motor by interchanging field leads
Figure 2: Reversing of a two-pole series motor by interchanging field leads

A shunt motor has the direction of rotation changed in the same manner as a series motor. To reverse a shunt-interpole motor, it is necessary to reverse the current flow through both the armature and the interpoles as a unit, figure 3.

Reversing the armature leads without the interpole will cause the motor to have incorrect interpole polarity, which will make the motor run excessively hot and will produce sparking at the brushes.

two-pole shunt-interpole motor with its armature and leads are reversed as a unit.
Figure 3: A two-pole shunt-interpole motor with its armature and leads are reversed as a unit.

With reversing a two-pole, compound-interpole motor, the interpoles are connected in series with the armature as shown in figure 4, and two wires A1 and A2 are brought out from this as a unit. To reverse this motor, it is necessary to reverse the interpole and armature circuit as a unit, figure 5.

two-pole compound-interpole motor with six wires brought out of the motor.
Figure 4: A two-pole compound-interpole motor with six wires brought out of the motor.


armature circuit including interpole reversed as a unit for opposite rotation
Figure 5: The armature circuit including interpole reversed as a unit for opposite rotation from that of figure 4.


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