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
+−48 VRa​ = 0.2 ΩIa​ = 25 AM+−E = ?ωT

A DC motor runs from a 48 V supply and draws an armature current of 25 A. Its armature resistance is 0.2 Ω. Find the back-EMF E.

V = 48 VIa = 25 ARa = 0.2 Ω
E = V
2.Easy
+−240 VRa​ = 0.8 ΩIa​ = 15 AM+−E = ?ωT

A DC motor runs from a 240 V supply and draws an armature current of 15 A. Its armature resistance is 0.8 Ω. Find the back-EMF E.

V = 240 VIa = 15 ARa = 0.8 Ω
E = V
3.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 5.5 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 5.5 kWn = 1200 rpm
T = N·m
4.Medium
T (N·m)n (rpm)2.4 N·mn0​n = ?

A DC motor (k = 0.4 N·m/A, Ra = 1 Ω) runs from 110 V and drives a load torque of 2.4 N·m. Find its speed n in rpm.

V = 110 Vk = 0.4 N·m/ARa = 1 ΩT = 2.4 N·m
n = rpm
5.Hard
T (N·m)n (rpm)1.8 N·m500 rpm

A DC motor with k = 0.3 V·s/rad and Ra = 0.25 Ω must drive a load of 1.8 N·m at 500 rpm. Find the armature voltage V it needs.

k = 0.3 V·s/radRa = 0.25 ΩT = 1.8 N·mn = 500 rpm
V = V
6.Hard
T (N·m)n (rpm)1.2 N·m900 rpm

A DC motor with k = 0.12 V·s/rad and Ra = 0.25 Ω must drive a load of 1.2 N·m at 900 rpm. Find the armature voltage V it needs.

k = 0.12 V·s/radRa = 0.25 ΩT = 1.2 N·mn = 900 rpm
V = V

Answer key

  1. 1. E = 43 V
  2. 2. E = 228 V
  3. 3. T = 43.77 N·m
  4. 4. n = 2483 rpm
  5. 5. V = 17.21 V
  6. 6. V = 13.81 V

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