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
+−220 VRa​ = 0.25 ΩIa​ = 40 AM+−EωT

A DC motor runs from 220 V with an armature current of 40 A. The armature resistance is 0.25 Ω. Find the developed (electromagnetic) power Pdev.

V = 220 VIa = 40 ARa = 0.25 Ω
Pdev = W
2.Easy
+−110 VRa​ = 2 ΩIa​ = ?M+−E = 0n = 0T

A DC motor with an armature resistance of 2 Ω is switched directly onto a 110 V supply. Its normal full-load current is 5 A. Find the armature current Istart at the moment of starting.

V = 110 VRa = 2 Ω
Istart = A
3.Medium
T (N·m)n (rpm)n0​ = ?

A DC motor with k = 0.25 V·s/rad runs from 24 V. Neglecting all losses at no load, find its no-load speed n0 in rpm.

V = 24 Vk = 0.25 V·s/rad
n0 = rpm
4.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 1.2 N·m/A and Ra = 1.2 Ω is connected to 220 V. Find its stall torque Tstall, the torque at zero speed.

V = 220 Vk = 1.2 N·m/ARa = 1.2 Ω
Tstall = N·m
5.Hard
+−240 VD = ?Ra​ = 2 ΩM+−En = 1500 rpmT = 5 N·m

A DC chopper feeds a motor (k = 1 V·s/rad, Ra = 2 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 1500 rpm with a load of 5 N·m.

Vdc = 240 Vk = 1 V·s/radRa = 2 ΩT = 5 N·mn = 1500 rpm
D = %
6.Hard
+−110 VD = ?Ra​ = 0.2 ΩM+−En = 600 rpmT = 18.75 N·m

A DC chopper feeds a motor (k = 0.75 V·s/rad, Ra = 0.2 Ω) from a 110 V DC bus. The average armature voltage is D·110 V. Find the duty cycle D that runs the motor at 600 rpm with a load of 18.75 N·m.

Vdc = 110 Vk = 0.75 V·s/radRa = 0.2 ΩT = 18.75 N·mn = 600 rpm
D = %

Answer key

  1. 1. Pdev = 8400 W
  2. 2. Istart = 55 A
  3. 3. n0 = 916.7 rpm
  4. 4. Tstall = 220 N·m
  5. 5. D = 69.62 %
  6. 6. D = 47.39 %

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