Series Wound DC Motor
A series-wound DC motor has its the field winding connectes in series with its armature winding.
Examining the Characteristics of Series DC Wound motor
Because the field winding of the stator is in series with the windings in the armature, the armature current simultaneously corresponds to the field, which causes the magnetic flux Φ in both windings. This results in a typical series connection behavior. The typical speed-torque characteristic of the series-wound motor is shown below.
Why so? Torque T is proportional to the Mangnetic flux M ∼ Φ
Magnetic flux of the field winding is proportional to the current Φfield ∼ I
Magnetic flux of the armature winding is proportional to the current Φarmature ∼ I
=> in "total": M proportional to I2 (M ∼ I2)
Series DC Wound motor should never be run with no load attached to them! At no load this motor will rotate with dangerously high speed.
Reversing a Series DC Wound motor
The direction of rotation of a Series DC Wound motor can be reversed by changing the polarity of either the armature coil or the field coil.
Series motors are used wherever a high starting torque is required. E.g. in lifting equipment, as starter motors in combustion cars, in power tools, etc.