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​M+−E = 232 Vn = 1200 rpmT

A DC motor turns at 1200 rpm, and its back-EMF at that speed is 232 V. Find the motor constant k in V·s/rad.

E = 232 Vn = 1200 rpm
k = V·s/rad
2.Easy
+−110 VRa​ = 1 ΩIa​ = 4 AM+−EωT

A DC motor runs from 110 V with an armature current of 4 A. The armature resistance is 1 Ω. Find the developed (electromagnetic) power Pdev.

V = 110 VIa = 4 ARa = 1 Ω
Pdev = W
3.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 0.75 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 0.75 kWn = 1200 rpm
T = N·m
4.Medium
+−220 VRa​ = 1 ΩIa​ = 10 AM+−EωT

A DC motor draws 10 A from a 220 V supply. Its armature resistance is 1 Ω and its rotational (friction, windage and iron) losses are 168 W. Find its efficiency η.

V = 220 VIa = 10 ARa = 1 ΩProt = 168 W
η = %
5.Hard
+−24 VRa​ = 2 ΩM+−EωT

A small DC motor has an armature resistance of 2 Ω and runs from 24 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 24 VRa = 2 Ω
Pmax = W
6.Hard
+−110 VRa​ = 1 ΩM+−EωT

A small DC motor has an armature resistance of 1 Ω and runs from 110 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 110 VRa = 1 Ω
Pmax = W

Answer key

  1. 1. k = 1.846 V·s/rad
  2. 2. Pdev = 424 W
  3. 3. T = 5.968 N·m
  4. 4. η = 87.82 %
  5. 5. Pmax = 72 W
  6. 6. Pmax = 3025 W

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