Generator device

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If the electric consumers in the car are powered only by the battery, then due to the high current consumption, it will discharge very quickly. The battery is constantly recharged by the generator, which is driven by the crankshaft of the engine. When the generator is running, the electric current flowing through the excitation winding creates a magnetic flux around the rotor poles. When the rotor rotates, the south and north poles of the rotor pass under each stator tooth, the working magnetic flux passing through the stator teeth changes in magnitude and voltage. The alternating magnetic flux creates an electromotive force in the stator winding. The wedge-shaped rotor pole pieces are selected in such a way that it allows obtaining a curve of the electromotive force close to sinusoidal. Since the batteries accumulate only direct current, a rectifier on silicon diodes is built into the generator to convert alternating current into direct current. Silicon diodes are very sensitive to large voltage peaks.



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


The Fiesta is equipped with a 14-volt, 55-amp alternator (Fig. 15.3). The alternator produces two-thirds of this power at a rotation speed of 2,000 min⁻¹. The alternator drive—V-belt or poly-V-belt—depends on the additional equipment of the car.

Voltage regulator


At high generator rotor speed, when the generator voltage becomes more than 13.6–14.6 V, the voltage regulator locks and the current does not pass through the excitation winding. The generator voltage drops, the regulator unlocks and again passes the current through the excitation winding. The higher the generator rotor speed, the longer the regulator locks, and 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 a level of 13.8–14.5 V.

Modern alternators, like the one in your Fiesta, are virtually maintenance-free. The contact brushes last about 100,000 km under normal operating conditions. Generator repairs are carried out by auto repair shops.







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