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.

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1.Easy

A DC motor with k = 1.5 V·s/rad and an armature resistance of 0.4 Ω runs from 240 V and draws 50 A. Find its speed n in rpm.

V = 240 VR_a = 0.4 ΩI_a = 50 Ak = 1.5 V·s/rad

n = rpm

2.Easy

A DC motor with k = 2 V·s/rad and an armature resistance of 0.4 Ω runs from 220 V and draws 40 A. Find its speed n in rpm.

V = 220 VR_a = 0.4 ΩI_a = 40 Ak = 2 V·s/rad

n = rpm

3.Medium

A DC motor (k = 0.1 V·s/rad, R_a = 0.25 Ω) runs from 24 V. At full load it draws 12 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − n_FL)/n_FL in percent.

V = 24 Vk = 0.1 V·s/radR_a = 0.25 ΩI_FL = 12 A

SR = %

4.Medium

A DC motor with k = 0.6 N·m/A and R_a = 0.5 Ω is connected to 240 V. Find its stall torque T_stall, the torque at zero speed.

V = 240 Vk = 0.6 N·m/AR_a = 0.5 Ω

T_stall = N·m

5.Hard

A small DC motor has an armature resistance of 4 Ω and runs from 110 V. Neglecting rotational losses, find the largest mechanical power P_max it can develop at any speed.

V = 110 VR_a = 4 Ω

P_max = W

6.Hard

A DC chopper feeds a motor (k = 2 V·s/rad, R_a = 0.2 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 600 rpm with a load of 80 N·m.

V_dc = 240 Vk = 2 V·s/radR_a = 0.2 ΩT = 80 N·mn = 600 rpm

D = %

Answer key

1. n = 1401 rpm
2. n = 974 rpm
3. SR = 14.29 %
4. T_stall = 288 N·m
5. P_max = 756.3 W
6. D = 55.69 %

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