Alternator

Bosch Alternator (Older Version), Rear View
1 – D+ connection (to battery charge indicator);
2 – B+ connection (to battery);
3 – voltage regulator;
4 – interference suppression capacitor.

The newer generation Bosch alternator can be identified by its cover (1). Position (2) shows the B+ cable to the battery.

Since the Audi 80 cannot draw power through an extension cable, electricity must be generated directly in the vehicle. This task is performed by the alternator, and not only for lighting, as was once the case, but for all electrical systems in the Audi.

Three-phase AC generator

Output
Until approximately December 1991, some versions of the Audi 80 were equipped with a 65-amp alternator; now only 90-amp alternators are installed. Special versions may have 110-amp or 120-amp alternators. To calculate alternator output, multiply the specified maximum current by the nominal voltage of 14 V. For example, 90 A x 14 V = 1260 W. As you have noticed, the alternator in the 12-volt electrical system actually produces 14 V. This is because charging current can only flow into the battery due to this small voltage difference.

The drive ratio from the crankshaft pulley to the alternator pulley is, incidentally, selected so that approximately 2/3 of the alternator output is produced at idle speed.

Alternator maintenance and safety
The three-phase AC generator has a fairly high output and produces current even at engine idle speed. Its sliding graphite contacts (brushes) last more than 80,000 km. As its name indicates, it produces alternating current, which is not used in the vehicle, since the battery can only be charged with direct current. Therefore, rectifier diodes are built into the alternator, converting alternating current into pulsating direct current. Since these diodes are sensitive to high voltage, observe the following:

With the alternator running, do not loosen or connect the wires between the battery and the alternator. This can cause a voltage surge (voltage spikes), which will damage the diodes.

The three-phase AC generator must not be operated without a properly connected, serviceable battery, because the battery acts as a buffer against overvoltage.

All cable connections between the three-phase AC generator, the battery, and the body metal or engine block (ground) must be secure. Even a loose contact can cause dangerous voltage spikes.

When quick-charging the battery (do not apply when charging with automatic shut-off chargers) and when performing electric welding on the body, both battery cables must be disconnected to prevent damage to the alternator diodes.