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 worksheetPractise 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
+−120 VRa​ = 0.5 ΩIa​ = 8 AM+−En = ?T

A DC motor with k = 0.6 V·s/rad and an armature resistance of 0.5 Ω runs from 120 V and draws 8 A. Find its speed n in rpm.

V = 120 VRa = 0.5 ΩIa = 8 Ak = 0.6 V·s/rad
n = rpm
2.Easy
+−110 VRa​ = 2 ΩIa​ = ?M+−E = 102 VωT

A DC motor on a 110 V supply has an armature resistance of 2 Ω. At its present speed the back-EMF is 102 V. Find the armature current Ia.

V = 110 VE = 102 VRa = 2 Ω
Ia = A
3.Medium
T (N·m)n (rpm)20 N·mn0​nFL​

A DC motor (k = 0.8 V·s/rad, Ra = 1.2 Ω) runs from 240 V. At full load it draws 25 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − nFL)/nFL in percent.

V = 240 Vk = 0.8 V·s/radRa = 1.2 ΩIFL = 25 A
SR = %
4.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 0.3 N·m/A and Ra = 1.2 Ω is connected to 110 V. Find its stall torque Tstall, the torque at zero speed.

V = 110 Vk = 0.3 N·m/ARa = 1.2 Ω
Tstall = N·m
5.Hard
+−240 VD = ?Ra​ = 0.5 ΩM+−En = 300 rpmT = 60 N·m

A DC chopper feeds a motor (k = 2 V·s/rad, Ra = 0.5 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 300 rpm with a load of 60 N·m.

Vdc = 240 Vk = 2 V·s/radRa = 0.5 ΩT = 60 N·mn = 300 rpm
D = %
6.Hard
+−220 VD = ?Ra​ = 1 ΩM+−En = 900 rpmT = 14.4 N·m

A DC chopper feeds a motor (k = 1.2 V·s/rad, Ra = 1 Ω) from a 220 V DC bus. The average armature voltage is D·220 V. Find the duty cycle D that runs the motor at 900 rpm with a load of 14.4 N·m.

Vdc = 220 Vk = 1.2 V·s/radRa = 1 ΩT = 14.4 N·mn = 900 rpm
D = %

Answer key

  1. 1. n = 1846 rpm
  2. 2. Ia = 4 A
  3. 3. SR = 14.29 %
  4. 4. Tstall = 27.5 N·m
  5. 5. D = 32.43 %
  6. 6. D = 56.86 %

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