A permanent magnet DC motor has an armature resistance of 05

A permanent magnet DC motor has an armature resistance of 0.5 ohm and when a voltage of 120 Vis applied to the motor it reaches a steady-state speed of rotation of 20 rev/s and draws 40 A. What will be the power loss in the armature and the power input to the motor?

Solution

Armature Resistance =R = 0.5

Voltage = V = 120 V

Speed = RPM = 20 rev/second

Current = I = 40 A

Answer a):

Loss = I²R = 40² X 0.5 = 800 W

Answer b):

Power input to DC Motor = P_input = VI = 120 * 40 = 4800 W