Generator Design
The generator is of AC type (alternator) with an integral voltage regulator.
It is driven by means of a multigroove belt from the crankshaft pulley and is accessible for service and removal when the front section of the right-hand wing liner has been removed.
The pulley is equipped with vanes to dissipate the heat which builds up in the generator. When the pulley rotates, the vanes draw in air through the generator to provide the necessary cooling. When the engine is switched off, the battery is the power source.
The generator acts as a "power station" when the engine is running and its purpose is to supply all items of electrical equipment with current.
Stator
The stator is fixed and consists of grooved plates which are insulated from each other and pressed together to make a fixed assembly.
The sinuous coils of the stator winding are installed in the grooves.
They are star-connected with 120° spacing and produce a three-phase AC supply.
Rotor with slip rings
The armature consists of two halves (claw-type poles) which mesh with each other. The two halves are pressed on the armature shaft. There are 12 claws in total on the armature, i.e. 12 poles.
One of the armature halves then has six north poles and the other half has six south poles.
The excitation winding is fixed on the armature shaft between the claw-type pole halves.
The excitation winding consists of a circular coil which is surrounded by the claw-type poles.
A comparatively low excitation current is applied through the carbon brushes in contact with the slip rings.
Integral fans
The heat build-up in the generator when it is in operation can damage the insulation, soldered joints and diodes. The generator has two integral fans which dissipate the heat.
The fans are driven by the armature shaft.
Cars equipped with a V6 engine also have an extra air intake to increase the flow of cooling air.
Rectifier
The alternating current (AC) produced by the generator (alternator) must be converted into direct current (DC) before it can be used in the car's electrical system.
It is converted by means of 6 (4-cylinder engines) or 12 (6-cylinder engines) zener diodes, 2 (4-cyl.) or 4 (6-cyl.) per phase winding.
If a phase is positive, the current from it flows through the positive diodes to B+. Conversely, if a phase is negative, the current from it flows through the negative diodes to D-.
Voltage regulator
The purpose of the voltage regulator is to maintain the current from the generator, whatever its speed and load demand, at a constant level regardless of engine rpm.
If the current generated exceeds the prescribed reference voltage (about 14 V), depending on the load, the voltage regulator will reduce or cut off the excitation current.
Generator excitation decreases and the voltage drops.
When the voltage has dropped below the reference level (about 14 V), excitation increases and with it the generator voltage until the reference level is again exceeded.
This cycle is repeated continuously.
Important points to bear in mind
You must:
- never disconnect the battery while the generator is running;
- never remove the generator while the battery is connected;
- never reverse the polarity of the battery (which could result in serious damage to the generator).
Generators (alternators) should be repaired by specialist workshops only.
It is extremely important that dismantling and testing are carried out correctly, as even minor errors can cause major damage.
Important: To avoid damage to the rectifier diodes, disconnect the negative battery cable and all generator connections before carrying out any electric welding on the car.