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 with k = 0.12 V·s/rad and an armature resistance of 1.5 Ω runs from 48 V and draws 4 A. Find its speed n in rpm.

V = 48 VR_a = 1.5 ΩI_a = 4 Ak = 0.12 V·s/rad

n = rpm

2.Easy

A DC motor with an armature resistance of 0.8 Ω is switched directly onto a 240 V supply. Its normal full-load current is 12 A. Find the armature current I_start at the moment of starting.

V = 240 VR_a = 0.8 Ω

I_start = A

3.Medium

A DC motor (k = 0.25 V·s/rad, R_a = 0.2 Ω) runs from 48 V. At full load it draws 30 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 = 0.2 ΩI_FL = 30 A

SR = %

4.Medium

A DC motor with k = 1.5 N·m/A and R_a = 0.25 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 = 0.25 Ω

T_stall = N·m

5.Hard

A DC chopper feeds a motor (k = 0.25 V·s/rad, R_a = 0.4 Ω) from a 24 V DC bus. The average armature voltage is D·24 V. Find the duty cycle D that runs the motor at 600 rpm with a load of 0.5 N·m.

V_dc = 24 Vk = 0.25 V·s/radR_a = 0.4 ΩT = 0.5 N·mn = 600 rpm

D = %

6.Hard

A DC motor (k = 0.75 V·s/rad, R_a = 0.5 Ω) on a fixed 110 V supply drives a load of 18.75 N·m. Find the series resistance R_s that slows it down to 500 rpm.

V = 110 Vk = 0.75 V·s/radR_a = 0.5 ΩT = 18.75 N·mn = 500 rpm

R_s = Ω

Answer key

1. n = 3342 rpm
2. I_start = 300 A
3. SR = 14.29 %
4. T_stall = 660 N·m
5. D = 68.78 %
6. R_s = 2.329 Ω

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