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
+−110 VRa​ = 1.5 ΩIa​ = 5 AM+−E = ?ωT

A DC motor runs from a 110 V supply and draws an armature current of 5 A. Its armature resistance is 1.5 Ω. Find the back-EMF E.

V = 110 VIa = 5 ARa = 1.5 Ω
E = V
2.Easy
+−220 VRa​ = 0.5 ΩIa​ = 25 AM+−E = ?ωT

A DC motor runs from a 220 V supply and draws an armature current of 25 A. Its armature resistance is 0.5 Ω. Find the back-EMF E.

V = 220 VIa = 25 ARa = 0.5 Ω
E = V
3.Medium
+−VRa​M+−En = 1500 rpmT = ?

A DC motor delivers 3 kW of mechanical power at 1500 rpm. Find the shaft torque T.

P = 3 kWn = 1500 rpm
T = N·m
4.Medium
+−VRa​M+−En = 2900 rpmT = ?

A DC motor delivers 5.5 kW of mechanical power at 2900 rpm. Find the shaft torque T.

P = 5.5 kWn = 2900 rpm
T = N·m
5.Hard
+−48 VRa​ = 2.5 ΩM+−EωT

A small DC motor has an armature resistance of 2.5 Ω and runs from 48 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 48 VRa = 2.5 Ω
Pmax = W
6.Hard
T (N·m)n (rpm)80 N·m750 rpm

A DC motor with k = 2 V·s/rad and Ra = 0.2 Ω must drive a load of 80 N·m at 750 rpm. Find the armature voltage V it needs.

k = 2 V·s/radRa = 0.2 ΩT = 80 N·mn = 750 rpm
V = V

Answer key

  1. 1. E = 102.5 V
  2. 2. E = 207.5 V
  3. 3. T = 19.1 N·m
  4. 4. T = 18.11 N·m
  5. 5. Pmax = 230.4 W
  6. 6. V = 165.1 V

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