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​Ia​ = 5 AM+−EωT = ?

A permanent-magnet DC motor has the torque constant k = 0.8 N·m/A. Find the torque T it develops at an armature current of 5 A.

k = 0.8 N·m/AIa = 5 A
T = N·m
2.Easy
+−240 VRa​ = 0.8 ΩIa​ = ?M+−E = 208 VωT

A DC motor on a 240 V supply has an armature resistance of 0.8 Ω. At its present speed the back-EMF is 208 V. Find the armature current Ia.

V = 240 VE = 208 VRa = 0.8 Ω
Ia = A
3.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 0.5 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 0.5 kWn = 1200 rpm
T = N·m
4.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 1 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 1 kWn = 1200 rpm
T = N·m
5.Hard
+−110 VD = ?Ra​ = 1.5 ΩM+−En = 750 rpmT = 3.2 N·m

A DC chopper feeds a motor (k = 0.4 V·s/rad, Ra = 1.5 Ω) from a 110 V DC bus. The average armature voltage is D·110 V. Find the duty cycle D that runs the motor at 750 rpm with a load of 3.2 N·m.

Vdc = 110 Vk = 0.4 V·s/radRa = 1.5 ΩT = 3.2 N·mn = 750 rpm
D = %
6.Hard
T (N·m)n (rpm)9.6 N·m600 rpm

A DC motor with k = 1.2 V·s/rad and Ra = 2 Ω must drive a load of 9.6 N·m at 600 rpm. Find the armature voltage V it needs.

k = 1.2 V·s/radRa = 2 ΩT = 9.6 N·mn = 600 rpm
V = V

Answer key

  1. 1. T = 4 N·m
  2. 2. Ia = 40 A
  3. 3. T = 3.979 N·m
  4. 4. T = 7.958 N·m
  5. 5. D = 39.47 %
  6. 6. V = 91.4 V

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