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
+−120 VRa​Ia​ = 30 AM+−EωT = ?

A permanent-magnet DC motor has the torque constant k = 2 N·m/A. Find the torque T it develops at an armature current of 30 A.

k = 2 N·m/AIa = 30 A
T = N·m
2.Easy
+−48 VRa​ = 0.25 ΩIa​ = ?M+−E = 0n = 0T

A DC motor with an armature resistance of 0.25 Ω is switched directly onto a 48 V supply. Its normal full-load current is 10 A. Find the armature current Istart at the moment of starting.

V = 48 VRa = 0.25 Ω
Istart = A
3.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 0.8 N·m/A and Ra = 0.25 Ω is connected to 110 V. Find its stall torque Tstall, the torque at zero speed.

V = 110 Vk = 0.8 N·m/ARa = 0.25 Ω
Tstall = N·m
4.Medium
+−VRa​M+−En = 2000 rpmT = ?

A DC motor delivers 1 kW of mechanical power at 2000 rpm. Find the shaft torque T.

P = 1 kWn = 2000 rpm
T = N·m
5.Hard
+−48 VRa​ = 0.8 ΩM+−EωT

A small DC motor has an armature resistance of 0.8 Ω and runs from 48 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 48 VRa = 0.8 Ω
Pmax = W
6.Hard
+−24 VRa​ = 0.5 ΩM+−EωT

A small DC motor has an armature resistance of 0.5 Ω and runs from 24 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 24 VRa = 0.5 Ω
Pmax = W

Answer key

  1. 1. T = 60 N·m
  2. 2. Istart = 192 A
  3. 3. Tstall = 352 N·m
  4. 4. T = 4.775 N·m
  5. 5. Pmax = 720 W
  6. 6. Pmax = 288 W

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