Generator device

If the electrical consumers in the car are powered only by the battery, then due to the large current consumption, its discharge will occur very quickly. The battery is constantly recharged by a generator driven by the engine crankshaft. When the generator is running, the electric current flowing through the field winding creates a magnetic flux around the rotor poles. When the rotor rotates under each stator tooth, then the south, then the north pole of the rotor passes, the working magnetic flux passing through the stator teeth changes in magnitude and voltage. The variable magnetic flux creates an electromotive force in the stator winding. The wedge-shaped shape of the pole pieces of the rotor is selected in such a way that it makes it possible to obtain the shape of the electromotive force curve close to sinusoidal. Since batteries store only direct current, a silicon diode rectifier is built into the generator to convert alternating current to direct current. Silicon diodes are very susceptible to large voltage peaks.



Pic. 15.3. Generator: 1 - V-ribbed belt pulley; 2 – fan; 3 – generator cover from the drive side; 4 - stator winding; 5 - bolt; 6 – rotor with two contact rings; 7 - generator cover with support bearing; 8 - rectifier; 9 - plastic casing; 10 - voltage regulator with brush holders


The Fiesta has a 14V 55A alternator (pic. 15.3). The generator generates two thirds of this power already at a speed of 2000 min^-1. The alternator drive - V-belt or V-ribbed belt - depends on the additional equipment of the car.

Voltage regulator

At a high frequency of rotation of the generator rotor, when the generator voltage becomes more than 13.6–14.6 V, the voltage regulator is locked and the current does not pass through the field winding. The generator voltage drops, the regulator opens and again passes current through the excitation winding. The higher the frequency of rotation of the generator rotor, the longer the time of the closed state of the regulator, therefore, the more the voltage at the generator output decreases. The process of locking and unlocking the regulator occurs at a high frequency, so the voltage fluctuations at the generator output are imperceptible, and the voltage can be considered constant, maintained at the level of 13.8–14.5 V.

Modern alternators, like the one in your Fiesta, are virtually maintenance-free. Contact brushes under normal operating conditions can withstand about 100,000 km of run. Repair of generators is carried out by auto repair shops.