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 5 A. The armature resistance is 0.4 Ω. Find the developed (electromagnetic) power P_dev.

V = 48 VI_a = 5 AR_a = 0.4 Ω

P_dev = W

2.Easy

A DC motor runs from 240 V with an armature current of 12 A. The armature resistance is 1.5 Ω. Find the developed (electromagnetic) power P_dev.

V = 240 VI_a = 12 AR_a = 1.5 Ω

P_dev = W

3.Medium

A DC motor with k = 0.6 V·s/rad runs from 220 V. Neglecting all losses at no load, find its no-load speed n₀ in rpm.

V = 220 Vk = 0.6 V·s/rad

n₀ = rpm

4.Medium

A DC motor (k = 0.2 V·s/rad, R_a = 1.5 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 = 0.2 V·s/radR_a = 1.5 ΩI_FL = 2 A

SR = %

5.Hard

A DC chopper feeds a motor (k = 0.2 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 800 rpm with a load of 0.4 N·m.

V_dc = 240 Vk = 0.2 V·s/radR_a = 0.4 ΩT = 0.4 N·mn = 800 rpm

D = %

6.Hard

A DC motor with k = 0.15 V·s/rad and R_a = 0.4 Ω must drive a load of 0.9 N·m at 300 rpm. Find the armature voltage V it needs.

k = 0.15 V·s/radR_a = 0.4 ΩT = 0.9 N·mn = 300 rpm

V = V

Answer key

1. P_dev = 230 W
2. P_dev = 2664 W
3. n₀ = 3501 rpm
4. SR = 6.667 %
5. D = 7.315 %
6. V = 7.112 V

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