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 turns at 600 rpm, and its back-EMF at that speed is 102.8 V. Find the motor constant k in V·s/rad.

E = 102.8 Vn = 600 rpm

k = V·s/rad

2.Easy

A DC motor with k = 1 V·s/rad and an armature resistance of 1.2 Ω runs from 240 V and draws 15 A. Find its speed n in rpm.

V = 240 VR_a = 1.2 ΩI_a = 15 Ak = 1 V·s/rad

n = rpm

3.Medium

A DC motor with k = 1.5 V·s/rad runs from 220 V. Neglecting all losses at no load, find its no-load speed n₀ in rpm.

V = 220 Vk = 1.5 V·s/rad

n₀ = rpm

4.Medium

A DC motor (k = 0.25 V·s/rad, R_a = 1 Ω) runs from 48 V. At full load it draws 2 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − n_FL)/n_FL in percent.

V = 48 Vk = 0.25 V·s/radR_a = 1 ΩI_FL = 2 A

SR = %

5.Hard

A DC motor (k = 1.2 V·s/rad, R_a = 0.4 Ω) on a fixed 120 V supply drives a load of 36 N·m. Find the series resistance R_s that slows it down to 750 rpm.

V = 120 Vk = 1.2 V·s/radR_a = 0.4 ΩT = 36 N·mn = 750 rpm

R_s = Ω

6.Hard

A DC chopper feeds a motor (k = 1.2 V·s/rad, R_a = 1 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 1000 rpm with a load of 30 N·m.

V_dc = 240 Vk = 1.2 V·s/radR_a = 1 ΩT = 30 N·mn = 1000 rpm

D = %

Answer key

1. k = 1.636 V·s/rad
2. n = 2120 rpm
3. n₀ = 1401 rpm
4. SR = 4.348 %
5. R_s = 0.4584 Ω
6. D = 62.78 %

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