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 25 A. The armature resistance is 0.5 Ω. Find the developed (electromagnetic) power P_dev.

V = 110 VI_a = 25 AR_a = 0.5 Ω

P_dev = W

2.Easy

A DC motor runs from 120 V with an armature current of 8 A. The armature resistance is 2 Ω. Find the developed (electromagnetic) power P_dev.

V = 120 VI_a = 8 AR_a = 2 Ω

P_dev = W

3.Medium

A DC motor with k = 1.2 N·m/A and R_a = 0.2 Ω is connected to 220 V. Find its stall torque T_stall, the torque at zero speed.

V = 220 Vk = 1.2 N·m/AR_a = 0.2 Ω

T_stall = N·m

4.Medium

A DC motor with k = 0.75 N·m/A and R_a = 0.25 Ω is connected to 220 V. Find its stall torque T_stall, the torque at zero speed.

V = 220 Vk = 0.75 N·m/AR_a = 0.25 Ω

T_stall = N·m

5.Hard

A separately excited DC motor (k = 1 V·s/rad at full field, R_a = 0.8 Ω, V = 220 V) drives a constant load torque of 10 N·m. The field flux is reduced to 70 % of its full value. Find the new speed n.

V = 220 Vk = 1 V·s/radR_a = 0.8 ΩT = 10 N·mΦ = 70 %

n = rpm

6.Hard

A DC chopper feeds a motor (k = 0.3 V·s/rad, R_a = 0.5 Ω) from a 110 V DC bus. The average armature voltage is D·110 V. Find the duty cycle D that runs the motor at 1500 rpm with a load of 2.4 N·m.

V_dc = 110 Vk = 0.3 V·s/radR_a = 0.5 ΩT = 2.4 N·mn = 1500 rpm

D = %

Answer key

1. P_dev = 2438 W
2. P_dev = 832 W
3. T_stall = 1320 N·m
4. T_stall = 660 N·m
5. n = 2845 rpm
6. D = 46.48 %

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