Adjusting Rocker of brush holders after assembly of a DC motor ...

 

 

 

The rocker can be brought back to more or less normal position as per the marking done before dismantling of the motor parts. However, for more accurate positioning, the following can be tried out.

 

Disconnect armature and field terminals from the control panel. Apply 230 volts AC supply to the field terminals. A variable transformer ( variac ) can be used to apply the voltage of a lower value. With all brushes in position, measure the AC voltage induced across the armature terminals on a multimeter. A small voltage of the  order of a few volts may be observed. Since the flux produced by the field winding and the flux produced by the armature current( when it flows ) are at 90 degrees to each other, there should be no voltage induced across the armature terminals in ideal situation. Now, adjust the rocker forward and backward slowly by a few degrees till the induced voltage is minimum. It may not become zero. Tighten the rocker in this position. This is the starting position when there is no armature current flowing. Armature current distorts the flux angle and rocker might need a minor adjustment after observing sparking on load.

 

By appling AC voltage to the excitation winding, i.e. field winding, we are making the motor act more like a transformer. Field winding is the Primary of the transformer and the armature winding is Secondary of the transformer. We expect the secondary winding to produce zero volts because the two windings are at supposed to be at Right angles to each other.

 

 

 

 

 

Common problems & symptoms

 

 

 

Bypassing interpoles

 

Rocker adjustment

 

Motor okay? Check Electronic parts

 

 

 

Drop Test for Armature

 

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