Power
Depending on the engine and configuration, we see in Audi A4 generators with a capacity of 70, 90 and 120 A. A 70-amp generator is serially installed on cars with four-cylinder engines, a 90-amp generator is included in the serial configuration of cars with six-cylinder engines and a 120-amp generator is included in the special equipment.
To determine the power of the generator, you need to multiply the indicated maximum current by the rated voltage of 14 V. For example, 90A X 14 V \u003d 1260 W.
You have already noticed: the alternator does supply 14V at 12V 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 chosen so that about 2/3 of the generator power can be produced already at idle.
Generator Handling and Precautions
The alternator, in addition to its rather high power, has a decisive advantage: it supplies current already at idle engine speed. In addition, its graphite brushes withstand mileage well in excess of 80,000 km. As the name implies, 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 generator, which convert the alternating current into a 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 lead to an increase in tension (voltage peaks) And «overheat» diode.
2. The alternator must not operate without a properly connected and serviceable battery. The battery serves as a buffer for the generator to some extent during voltage peaks.
3. All wiring connections between alternator, battery and body metal or engine block (weight) must be durable. Even a swinging contact can lead to power surges.
4. When accelerating battery charging (can not be used for charging at home) and during welding work on the body, both wires must be disconnected from the battery in order not to damage the generator diodes.
In models with four-cylinder engines, the alternator (2) is located on the left front next to the engine and is accessible from above. Numeric «1» the top mounting bolt is shown.
Bottom view of a six-cylinder engine. Generator (2) located on the lower right near the engine. An air duct is connected to cool the generator (1) (dismantled here for the sake of clarity of the image).
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