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 turns at 600 rpm, and its back-EMF at that speed is 105.6 V. Find the motor constant k in V·s/rad.

E = 105.6 Vn = 600 rpm

k = V·s/rad

2.Easy

A DC motor turns at 2400 rpm, and its back-EMF at that speed is 196 V. Find the motor constant k in V·s/rad.

E = 196 Vn = 2400 rpm

k = V·s/rad

3.Medium

A DC motor (k = 1 V·s/rad, R_a = 0.4 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 = 1 V·s/radR_a = 0.4 ΩI_FL = 12 A

SR = %

4.Medium

A DC motor delivers 2.2 kW of mechanical power at 750 rpm. Find the shaft torque T.

P = 2.2 kWn = 750 rpm

T = N·m

5.Hard

A DC chopper feeds a motor (k = 0.1 V·s/rad, R_a = 0.8 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 0.2 N·m.

V_dc = 240 Vk = 0.1 V·s/radR_a = 0.8 ΩT = 0.2 N·mn = 800 rpm

D = %

6.Hard

A separately excited DC motor on 220 V (R_a = 1.2 Ω) runs at 1200 rpm with an armature current of 10 A. The load changes and the current becomes 2.5 A, with the field unchanged. Find the new speed n₂.

V = 220 VR_a = 1.2 Ωn₁ = 1200 rpmI_a1 = 10 AI_a2 = 2.5 A

n₂ = rpm

Answer key

1. k = 1.681 V·s/rad
2. k = 0.7799 V·s/rad
3. SR = 4.167 %
4. T = 28.01 N·m
5. D = 4.157 %
6. n₂ = 1252 rpm

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