We employ this method when low speed and high torque are the operating requirements. Bipolar series-wound motors have current flowing in two directions through the full coil. However, in so doing, we're increasing the winding's inductance and therefore cutting down our usable speed. When using a motor in bipolar series fashion, changes occur not only in the torque and speed but also in the electrical characteristics. Because we're now using the coils in series, the resistance value increases by a factor of two.
Inductance also changes.
However, when we add two like inductors in series, we encounter a phenomenon known as mutual inductance. This mutual inductance causes the motor's inductance rating to increase by a factor of four, as shown in Example 1 . Eight-lead motors enable us to configure the windings for any method, bipolar or unipolar. This overlapping allows the current to flow in the same direction through both coils, which are now in parallel with each other. However, this performance gain comes at the expense of high current.