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 110 V with an armature current of 20 A. The armature resistance is 0.5 Ω. Find the developed (electromagnetic) power P_dev.

V = 110 VI_a = 20 AR_a = 0.5 Ω

P_dev = W

2.Easy

A DC motor with an armature resistance of 2 Ω is switched directly onto a 120 V supply. Its normal full-load current is 2 A. Find the armature current I_start at the moment of starting.

V = 120 VR_a = 2 Ω

I_start = A

3.Medium

A DC motor (k = 0.6 N·m/A, R_a = 1 Ω) runs from 48 V and drives a load torque of 2.4 N·m. Find its speed n in rpm.

V = 48 Vk = 0.6 N·m/AR_a = 1 ΩT = 2.4 N·m

n = rpm

4.Medium

A DC motor with k = 0.75 N·m/A and R_a = 0.5 Ω is connected to 240 V. Find its stall torque T_stall, the torque at zero speed.

V = 240 Vk = 0.75 N·m/AR_a = 0.5 Ω

T_stall = N·m

5.Hard

A DC chopper feeds a motor (k = 1 V·s/rad, R_a = 0.8 Ω) from a 120 V DC bus. The average armature voltage is D·120 V. Find the duty cycle D that runs the motor at 500 rpm with a load of 6 N·m.

V_dc = 120 Vk = 1 V·s/radR_a = 0.8 ΩT = 6 N·mn = 500 rpm

D = %

6.Hard

A DC motor (k = 0.3 V·s/rad, R_a = 0.8 Ω) on a fixed 120 V supply drives a load of 1.8 N·m. Find the series resistance R_s that slows it down to 300 rpm.

V = 120 Vk = 0.3 V·s/radR_a = 0.8 ΩT = 1.8 N·mn = 300 rpm

R_s = Ω

Answer key

1. P_dev = 2000 W
2. I_start = 60 A
3. n = 700.3 rpm
4. T_stall = 360 N·m
5. D = 47.63 %
6. R_s = 17.63 Ω

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