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 runs from 48 V with an armature current of 4 A. The armature resistance is 1.5 Ω. Find the developed (electromagnetic) power P_dev.

V = 48 VI_a = 4 AR_a = 1.5 Ω

P_dev = W

2.Easy

A DC motor with k = 0.15 V·s/rad and an armature resistance of 0.4 Ω runs from 48 V and draws 5 A. Find its speed n in rpm.

V = 48 VR_a = 0.4 ΩI_a = 5 Ak = 0.15 V·s/rad

n = rpm

3.Medium

A DC motor (k = 0.8 N·m/A, R_a = 0.8 Ω) runs from 220 V and drives a load torque of 12 N·m. Find its speed n in rpm.

V = 220 Vk = 0.8 N·m/AR_a = 0.8 ΩT = 12 N·m

n = rpm

4.Medium

A DC motor (k = 0.3 V·s/rad, R_a = 0.5 Ω) runs from 120 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 = 120 Vk = 0.3 V·s/radR_a = 0.5 ΩI_FL = 12 A

SR = %

5.Hard

A small DC motor has an armature resistance of 1 Ω and runs from 120 V. Neglecting rotational losses, find the largest mechanical power P_max it can develop at any speed.

V = 120 VR_a = 1 Ω

P_max = W

6.Hard

A DC chopper feeds a motor (k = 0.8 V·s/rad, R_a = 0.4 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 500 rpm with a load of 32 N·m.

V_dc = 240 Vk = 0.8 V·s/radR_a = 0.4 ΩT = 32 N·mn = 500 rpm

D = %

Answer key

1. P_dev = 168 W
2. n = 2928 rpm
3. n = 2483 rpm
4. SR = 5.263 %
5. P_max = 3600 W
6. D = 24.12 %

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