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 = 0.6 V·s/rad and an armature resistance of 2 Ω runs from 220 V and draws 10 A. Find its speed n in rpm.

V = 220 VR_a = 2 ΩI_a = 10 Ak = 0.6 V·s/rad

n = rpm

2.Easy

A permanent-magnet DC motor has the torque constant k = 1.5 N·m/A. Find the torque T it develops at an armature current of 30 A.

k = 1.5 N·m/AI_a = 30 A

T = N·m

3.Medium

A DC motor with k = 0.1 V·s/rad runs from 24 V. Neglecting all losses at no load, find its no-load speed n₀ in rpm.

V = 24 Vk = 0.1 V·s/rad

n₀ = rpm

4.Medium

A DC motor with k = 0.8 N·m/A and R_a = 0.4 Ω is connected to 110 V. Find its stall torque T_stall, the torque at zero speed.

V = 110 Vk = 0.8 N·m/AR_a = 0.4 Ω

T_stall = N·m

5.Hard

A DC chopper feeds a motor (k = 0.75 V·s/rad, R_a = 0.5 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 9 N·m.

V_dc = 240 Vk = 0.75 V·s/radR_a = 0.5 ΩT = 9 N·mn = 600 rpm

D = %

6.Hard

A separately excited DC motor on 220 V (R_a = 0.5 Ω) runs at 1000 rpm with an armature current of 50 A. The load changes and the current becomes 75 A, with the field unchanged. Find the new speed n₂.

V = 220 VR_a = 0.5 Ωn₁ = 1000 rpmI_a1 = 50 AI_a2 = 75 A

n₂ = rpm

Answer key

1. n = 3183 rpm
2. T = 45 N·m
3. n₀ = 2292 rpm
4. T_stall = 220 N·m
5. D = 22.13 %
6. n₂ = 935.9 rpm

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