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
+−240 VRa​ = 1 ΩIa​ = 25 AM+−EωT

A DC motor runs from 240 V with an armature current of 25 A. The armature resistance is 1 Ω. Find the developed (electromagnetic) power Pdev.

V = 240 VIa = 25 ARa = 1 Ω
Pdev = W
2.Easy
+−220 VRa​ = 0.5 ΩIa​ = 30 AM+−EωT

A DC motor runs from 220 V with an armature current of 30 A. The armature resistance is 0.5 Ω. Find the developed (electromagnetic) power Pdev.

V = 220 VIa = 30 ARa = 0.5 Ω
Pdev = W
3.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 0.3 N·m/A and Ra = 0.2 Ω is connected to 120 V. Find its stall torque Tstall, the torque at zero speed.

V = 120 Vk = 0.3 N·m/ARa = 0.2 Ω
Tstall = N·m
4.Medium
+−VRa​M+−En = 3000 rpmT = ?

A DC motor delivers 7.5 kW of mechanical power at 3000 rpm. Find the shaft torque T.

P = 7.5 kWn = 3000 rpm
T = N·m
5.Hard
+−220 VD = ?Ra​ = 2 ΩM+−En = 300 rpmT = 9 N·m

A DC chopper feeds a motor (k = 0.75 V·s/rad, Ra = 2 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 300 rpm with a load of 9 N·m.

Vdc = 220 Vk = 0.75 V·s/radRa = 2 ΩT = 9 N·mn = 300 rpm
D = %
6.Hard
+−110 VRa​ = 2 ΩM+−EωT

A small DC motor has an armature resistance of 2 Ω and runs from 110 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 110 VRa = 2 Ω
Pmax = W

Answer key

  1. 1. Pdev = 5375 W
  2. 2. Pdev = 6150 W
  3. 3. Tstall = 180 N·m
  4. 4. T = 23.87 N·m
  5. 5. D = 21.62 %
  6. 6. Pmax = 1513 W

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