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
+−220 VRa​ = 2 ΩIa​ = 6 AM+−EωT

A DC motor runs from 220 V with an armature current of 6 A. The armature resistance is 2 Ω. Find the developed (electromagnetic) power Pdev.

V = 220 VIa = 6 ARa = 2 Ω
Pdev = W
2.Easy
+−48 VRa​M+−E = 45.5 Vn = 900 rpmT

A DC motor turns at 900 rpm, and its back-EMF at that speed is 45.5 V. Find the motor constant k in V·s/rad.

E = 45.5 Vn = 900 rpm
k = V·s/rad
3.Medium
T (N·m)n (rpm)n0​ = ?

A DC motor with k = 1.5 V·s/rad runs from 220 V. Neglecting all losses at no load, find its no-load speed n0 in rpm.

V = 220 Vk = 1.5 V·s/rad
n0 = rpm
4.Medium
+−VRa​M+−En = 750 rpmT = ?

A DC motor delivers 2.2 kW of mechanical power at 750 rpm. Find the shaft torque T.

P = 2.2 kWn = 750 rpm
T = N·m
5.Hard
T (N·m)n (rpm)37.5 N·m800 rpm

A DC motor with k = 1.5 V·s/rad and Ra = 1 Ω must drive a load of 37.5 N·m at 800 rpm. Find the armature voltage V it needs.

k = 1.5 V·s/radRa = 1 ΩT = 37.5 N·mn = 800 rpm
V = V
6.Hard
+−240 VD = ?Ra​ = 2 ΩM+−En = 750 rpmT = 12 N·m

A DC chopper feeds a motor (k = 1.2 V·s/rad, Ra = 2 Ω) from a 240 V DC bus. The average armature voltage is D·240 V. Find the duty cycle D that runs the motor at 750 rpm with a load of 12 N·m.

Vdc = 240 Vk = 1.2 V·s/radRa = 2 ΩT = 12 N·mn = 750 rpm
D = %

Answer key

  1. 1. Pdev = 1248 W
  2. 2. k = 0.4828 V·s/rad
  3. 3. n0 = 1401 rpm
  4. 4. T = 28.01 N·m
  5. 5. V = 150.7 V
  6. 6. D = 47.6 %

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