Effect of Armature Resistance on Armature Current in a DC Motor

When the load torque of a DC motor is constant, the armature current is directly proportional to the armature resistance. So, the effect of armature resistance on armature current is as follows:

1. Increase in Armature Resistance

If the armature resistance of a DC motor increases, the armature current will also increase. This is because the total voltage drop across the armature circuit (i.e., the sum of the voltage drops across the armature resistance and the back EMF) remains constant. Therefore, according to Ohm's law, an increase in armature resistance leads to an increase in armature current.

2. Decrease in Armature Resistance

If the armature resistance of a DC motor decreases, the armature current will also decrease. This is because the total voltage drop across the armature circuit remains constant, and a decrease in armature resistance leads to a decrease in armature current according to Ohm's law.

3. Importance of Armature Current

The armature current is a crucial parameter in a DC motor as it determines the amount of torque that the motor can produce. The torque produced by a DC motor is directly proportional to the armature current. Therefore, any change in armature resistance affects the armature current and, consequently, the motor's torque.

Conclusion

In summary, when the load torque of a DC motor is constant, an increase in armature resistance leads to an increase in armature current, while a decrease in armature resistance leads to a decrease in armature current. The armature current is a critical parameter that determines the motor's torque, and any change in armature resistance affects the torque produced by the motor.