Table of contents: Power ↓ Generator Handling and Precautions ↓
Since the Audi cannot pull a wire to supply current, the current must be produced directly in the car. This task is performed by the generator. But not only for the sake of light, as one might assume, but to supply electricity to all equipment in the Audi.
Power
Depending on the engine and configuration, we see generators with a capacity of 70, 90 and 120 A in the Audi A4. The 70-amp generator is installed as standard on cars with four-cylinder engines, the 90-amp generator is included in the standard equipment of cars with six-cylinder engines and the 120-amp generator is included in the special equipment.
To determine the generator power, you need to multiply the specified maximum current by the nominal voltage of 14 V. For example, 90A X 14 V = 1260 W.
You have already noticed: the generator actually supplies 14 V at 12 V in the on-board network. That is, only with such a small difference in voltage can current flow to the battery in order to charge it.
The transmission from the crankshaft belt pulley to the generator belt pulley is selected in such a way that already at idle speed about 2/3 of the generator power can be produced.
Generator Handling and Precautions
The alternator, in addition to its relatively high power, has a decisive advantage: it supplies current already at idle speed. In addition, its graphite brushes can withstand a mileage of significantly more than 80,000 km. As the name suggests, it produces alternating current, which we cannot use in a car, since the battery can, of course, only store direct current. Therefore, three diode rectifiers are built into the alternating current, which convert alternating current into pulsating direct current. These diodes are sensitive to high voltages, and therefore you should consider the following points:
1. When the engine is running, do not remove or connect any wire between the battery and the generator. This can cause the voltage to increase sharply (voltage peaks) and "overheat" the diode.
2. The alternator should not operate without a properly connected and functioning battery. The battery serves as a buffer for the alternator to some extent during voltage peaks.
3. All wire connections between the alternator, battery, and body metal or engine block (ground) must be tight. Even a swinging contact can cause voltage surges.
4. When charging the battery at high speed (cannot be used for charging at home) and when welding on the body, both wires must be disconnected from the battery in order not to damage the generator diodes.
On models with four-cylinder engines, the alternator (2) is located on the left front next to the engine and is accessible from above. The number "1" shows the upper mounting bolt.
View of a six-cylinder engine from below. The generator (2) is located on the right side at the bottom near the engine. An air duct (1) is connected to cool the generator (here dismantled for the sake of clarity of the image).