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​ = 0.25 ΩIa​ = ?M+−E = 210 VωT

A DC motor on a 220 V supply has an armature resistance of 0.25 Ω. At its present speed the back-EMF is 210 V. Find the armature current Ia.

V = 220 VE = 210 VRa = 0.25 Ω
Ia = A
2.Easy
+−220 VRa​ = 0.5 ΩIa​ = 25 AM+−EωT

A DC motor runs from 220 V with an armature current of 25 A. The armature resistance is 0.5 Ω. Find the developed (electromagnetic) power Pdev.

V = 220 VIa = 25 ARa = 0.5 Ω
Pdev = W
3.Medium
+−VRa​M+−En = 960 rpmT = ?

A DC motor delivers 1 kW of mechanical power at 960 rpm. Find the shaft torque T.

P = 1 kWn = 960 rpm
T = N·m
4.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 0.25 N·m/A and Ra = 0.5 Ω is connected to 24 V. Find its stall torque Tstall, the torque at zero speed.

V = 24 Vk = 0.25 N·m/ARa = 0.5 Ω
Tstall = N·m
5.Hard
+−220 VD = ?Ra​ = 1 ΩM+−En = 800 rpmT = 0.24 N·m

A DC chopper feeds a motor (k = 0.12 V·s/rad, Ra = 1 Ω) from a 220 V DC bus. The average armature voltage is D·220 V. Find the duty cycle D that runs the motor at 800 rpm with a load of 0.24 N·m.

Vdc = 220 Vk = 0.12 V·s/radRa = 1 ΩT = 0.24 N·mn = 800 rpm
D = %
6.Hard
T (N·m)n (rpm)30 N·m1500 rpm

A DC motor with k = 1.2 V·s/rad and Ra = 1 Ω must drive a load of 30 N·m at 1500 rpm. Find the armature voltage V it needs.

k = 1.2 V·s/radRa = 1 ΩT = 30 N·mn = 1500 rpm
V = V

Answer key

  1. 1. Ia = 40 A
  2. 2. Pdev = 5188 W
  3. 3. T = 9.947 N·m
  4. 4. Tstall = 12 N·m
  5. 5. D = 5.479 %
  6. 6. V = 213.5 V

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