In this type of motor, the series field winding is connected in series with the armature and the supply, as shown in the Fig. 1.
|Fig. 1 D.C. series motor|
Let Rse be the resistance of the series field winding. The value of Rse is very small and it is made of small number of turns having large cross-sectional area.
1.1 Voltage and Current Relationship
Let IL be the total current drawn from the supply.
So IL = Ise = Ia
and V = Eb + Ia Ra + Ise Rse + Vbrush
V = Eb + Ia (Ra + Rse) + Vbrush
Supply voltage has to overcome the drop across series field winding in addition to Eb and drop across armature winding.
Note : In series motor, entire armature current is passing through the series field winding. So flux produced is proportional to the armature current.