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​ = 1 ΩIa​ = ?M+−E = 195 VωT

A DC motor on a 220 V supply has an armature resistance of 1 Ω. At its present speed the back-EMF is 195 V. Find the armature current Ia.

V = 220 VE = 195 VRa = 1 Ω
Ia = A
2.Easy
+−220 VRa​ = 0.25 ΩIa​ = 40 AM+−EωT

A DC motor runs from 220 V with an armature current of 40 A. The armature resistance is 0.25 Ω. Find the developed (electromagnetic) power Pdev.

V = 220 VIa = 40 ARa = 0.25 Ω
Pdev = W
3.Medium
T (N·m)n (rpm)10 N·mn0​nFL​

A DC motor (k = 0.5 V·s/rad, Ra = 0.4 Ω) runs from 110 V. At full load it draws 20 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − nFL)/nFL in percent.

V = 110 Vk = 0.5 V·s/radRa = 0.4 ΩIFL = 20 A
SR = %
4.Medium
T (N·m)n (rpm)12 N·mn0​n = ?

A DC motor (k = 0.6 N·m/A, Ra = 0.8 Ω) runs from 220 V and drives a load torque of 12 N·m. Find its speed n in rpm.

V = 220 Vk = 0.6 N·m/ARa = 0.8 ΩT = 12 N·m
n = rpm
5.Hard
T (N·m)n (rpm)12 N·m300 rpm

A DC motor with k = 1.2 V·s/rad and Ra = 0.4 Ω must drive a load of 12 N·m at 300 rpm. Find the armature voltage V it needs.

k = 1.2 V·s/radRa = 0.4 ΩT = 12 N·mn = 300 rpm
V = V
6.Hard
T (N·m)n (rpm)1 N·m750 rpm

A DC motor with k = 0.25 V·s/rad and Ra = 0.5 Ω must drive a load of 1 N·m at 750 rpm. Find the armature voltage V it needs.

k = 0.25 V·s/radRa = 0.5 ΩT = 1 N·mn = 750 rpm
V = V

Answer key

  1. 1. Ia = 25 A
  2. 2. Pdev = 8400 W
  3. 3. SR = 7.843 %
  4. 4. n = 3247 rpm
  5. 5. V = 41.7 V
  6. 6. V = 21.63 V

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