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

A DC motor turns at 1800 rpm, and its back-EMF at that speed is 210 V. Find the motor constant k in V·s/rad.

E = 210 Vn = 1800 rpm

k = V·s/rad

2.Easy

A DC motor with an armature resistance of 1.5 Ω is switched directly onto a 240 V supply. Its normal full-load current is 6 A. Find the armature current I_start at the moment of starting.

V = 240 VR_a = 1.5 Ω

I_start = A

3.Medium

A DC motor (k = 0.4 V·s/rad, R_a = 0.25 Ω) runs from 48 V. At full load it draws 6 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − n_FL)/n_FL in percent.

V = 48 Vk = 0.4 V·s/radR_a = 0.25 ΩI_FL = 6 A

SR = %

4.Medium

A DC motor (k = 0.5 V·s/rad, R_a = 0.8 Ω) runs from 48 V. At full load it draws 5 A. Neglecting the no-load current, find its speed regulation SR = (n₀ − n_FL)/n_FL in percent.

V = 48 Vk = 0.5 V·s/radR_a = 0.8 ΩI_FL = 5 A

SR = %

5.Hard

A DC motor (k = 0.75 V·s/rad, R_a = 1.5 Ω) on a fixed 48 V supply drives a load of 1.5 N·m. Find the series resistance R_s that slows it down to 500 rpm.

V = 48 Vk = 0.75 V·s/radR_a = 1.5 ΩT = 1.5 N·mn = 500 rpm

R_s = Ω

6.Hard

A DC motor with k = 0.25 V·s/rad and R_a = 0.2 Ω must drive a load of 2 N·m at 500 rpm. Find the armature voltage V it needs.

k = 0.25 V·s/radR_a = 0.2 ΩT = 2 N·mn = 500 rpm

V = V

Answer key

1. k = 1.114 V·s/rad
2. I_start = 160 A
3. SR = 3.226 %
4. SR = 9.091 %
5. R_s = 2.865 Ω
6. V = 14.69 V

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