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 permanent-magnet DC motor has the torque constant k = 0.25 N·m/A. Find the torque T it develops at an armature current of 30 A.

k = 0.25 N·m/AI_a = 30 A

T = N·m

2.Easy

A DC motor turns at 1000 rpm, and its back-EMF at that speed is 21.6 V. Find the motor constant k in V·s/rad.

E = 21.6 Vn = 1000 rpm

k = V·s/rad

3.Medium

A DC motor with k = 1 N·m/A and R_a = 0.2 Ω is connected to 110 V. Find its stall torque T_stall, the torque at zero speed.

V = 110 Vk = 1 N·m/AR_a = 0.2 Ω

T_stall = N·m

4.Medium

A DC motor (k = 0.08 N·m/A, R_a = 0.25 Ω) runs from 24 V and drives a load torque of 0.8 N·m. Find its speed n in rpm.

V = 24 Vk = 0.08 N·m/AR_a = 0.25 ΩT = 0.8 N·m

n = rpm

5.Hard

A DC chopper feeds a motor (k = 0.75 V·s/rad, R_a = 1 Ω) from a 220 V DC bus. The average armature voltage is D·220 V. Find the duty cycle D that runs the motor at 500 rpm with a load of 7.5 N·m.

V_dc = 220 Vk = 0.75 V·s/radR_a = 1 ΩT = 7.5 N·mn = 500 rpm

D = %

6.Hard

A DC chopper feeds a motor (k = 0.25 V·s/rad, R_a = 1.2 Ω) from a 48 V DC bus. The average armature voltage is D·48 V. Find the duty cycle D that runs the motor at 900 rpm with a load of 0.5 N·m.

V_dc = 48 Vk = 0.25 V·s/radR_a = 1.2 ΩT = 0.5 N·mn = 900 rpm

D = %

Answer key

1. T = 7.5 N·m
2. k = 0.2063 V·s/rad
3. T_stall = 550 N·m
4. n = 2566 rpm
5. D = 22.4 %
6. D = 54.09 %

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