DC motors worksheet with answers

Free printable DC motors worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

New worksheet Practise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________ Date: ____________

1.Easy

A DC motor runs from a 48 V supply and draws an armature current of 25 A. Its armature resistance is 0.25 Ω. Find the back-EMF E.

V = 48 VI_a = 25 AR_a = 0.25 Ω

E = V

2.Easy

A DC motor runs from 220 V with an armature current of 25 A. The armature resistance is 0.5 Ω. Find the developed (electromagnetic) power P_dev.

V = 220 VI_a = 25 AR_a = 0.5 Ω

P_dev = W

3.Medium

A DC motor with k = 1.5 N·m/A and R_a = 2 Ω is connected to 110 V. Find its stall torque T_stall, the torque at zero speed.

V = 110 Vk = 1.5 N·m/AR_a = 2 Ω

T_stall = N·m

4.Medium

A DC motor (k = 0.8 N·m/A, R_a = 0.5 Ω) runs from 220 V and drives a load torque of 32 N·m. Find its speed n in rpm.

V = 220 Vk = 0.8 N·m/AR_a = 0.5 ΩT = 32 N·m

n = rpm

5.Hard

A DC chopper feeds a motor (k = 1.5 V·s/rad, R_a = 0.4 Ω) from a 240 V DC bus. The average armature voltage is D·240 V. Find the duty cycle D that runs the motor at 750 rpm with a load of 60 N·m.

V_dc = 240 Vk = 1.5 V·s/radR_a = 0.4 ΩT = 60 N·mn = 750 rpm

D = %

6.Hard

A DC chopper feeds a motor (k = 0.08 V·s/rad, R_a = 0.4 Ω) from a 120 V DC bus. The average armature voltage is D·120 V. Find the duty cycle D that runs the motor at 1500 rpm with a load of 0.32 N·m.

V_dc = 120 Vk = 0.08 V·s/radR_a = 0.4 ΩT = 0.32 N·mn = 1500 rpm

D = %

Answer key

1. E = 41.75 V
2. P_dev = 5188 W
3. T_stall = 82.5 N·m
4. n = 2387 rpm
5. D = 55.75 %
6. D = 11.81 %

Full step-by-step solutions: practise this topic on examproblems.com.