Generator — general information and device (BMW 5 Series E39)

The BMW 5 Series is equipped with an alternator. Depending on the model and version, alternators with a rated current of 80 A to 140 A can be installed.

The generator is driven by a poly-V belt from the crankshaft. The rotor with the excitation winding rotates relative to the stationary stator.

Through the brushes and slip rings, the excitation current flows through the excitation winding. This creates a magnetic field.

The position of the magnetic field relative to the stator constantly changes in accordance with the rotor speed. Due to this, alternating current occurs in the stator winding.

But since the battery can only be charged with direct current, the alternating current is converted into direct current using a rectifier on semiconductor diodes. The relay-regulator changes the charging current by switching the excitation current on and off in accordance with the charge level of the battery. At the same time, the relay-regulator maintains the operating voltage constant and equal to approximately 14 volts, regardless of the rotation frequency of the generator rotor.