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​ = 1.5 ΩIa​ = 8 AM+−En = ?T

A DC motor with k = 0.3 V·s/rad and an armature resistance of 1.5 Ω runs from 120 V and draws 8 A. Find its speed n in rpm.

V = 120 VRa = 1.5 ΩIa = 8 Ak = 0.3 V·s/rad
n = rpm
2.Easy
+−24 VRa​ = 0.8 ΩIa​ = 2 AM+−EωT

A DC motor runs from 24 V with an armature current of 2 A. The armature resistance is 0.8 Ω. Find the developed (electromagnetic) power Pdev.

V = 24 VIa = 2 ARa = 0.8 Ω
Pdev = W
3.Medium
+−VRa​M+−En = 2900 rpmT = ?

A DC motor delivers 11 kW of mechanical power at 2900 rpm. Find the shaft torque T.

P = 11 kWn = 2900 rpm
T = N·m
4.Medium
T (N·m)n (rpm)4.5 N·mn0​nFL​

A DC motor (k = 0.75 V·s/rad, Ra = 1 Ω) runs from 110 V. At full load it draws 6 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − nFL)/nFL in percent.

V = 110 Vk = 0.75 V·s/radRa = 1 ΩIFL = 6 A
SR = %
5.Hard
T (N·m)n (rpm)7.5 N·m900 rpm

A DC motor with k = 0.75 V·s/rad and Ra = 1.2 Ω must drive a load of 7.5 N·m at 900 rpm. Find the armature voltage V it needs.

k = 0.75 V·s/radRa = 1.2 ΩT = 7.5 N·mn = 900 rpm
V = V
6.Hard
+−110 VD = ?Ra​ = 0.5 ΩM+−En = 800 rpmT = 0.24 N·m

A DC chopper feeds a motor (k = 0.12 V·s/rad, Ra = 0.5 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 800 rpm with a load of 0.24 N·m.

Vdc = 110 Vk = 0.12 V·s/radRa = 0.5 ΩT = 0.24 N·mn = 800 rpm
D = %

Answer key

  1. 1. n = 3438 rpm
  2. 2. Pdev = 44.8 W
  3. 3. T = 36.22 N·m
  4. 4. SR = 5.769 %
  5. 5. V = 82.69 V
  6. 6. D = 10.05 %

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