Alternator and components – operation

With the alternator not working and the ignition key in the ON position, the body computer lights up the warning light in the instrument panel (NQS) and sends a power supply to the voltage regulator incorporated in the actual alternator via terminal

D+.

In these conditions the energizing circuit (rotor) is enabled to earth by the regulator electronics.

With the alternator rotating through the effect of the alteration in the number of revs and the mangetic field, a three-phase alternating volage is produced in the electrical circuit (stator) which, rectified by the diode bridge, can come out of

terminal B+.

When the upper fixed calibration level is reached (13.7 - 14.2 V) the battery is charged and the system supplied.

The body computer checks the efficiency of the alternator recharging system by measuring two parameters: the voltage signal coming from alternator terminal D+ and the engine rpm signal received at the CAN network from the injection control unit (NCM).

The lighting up of the warning light in the instrument panel (NQS) is determined by the levels recognized by the body computer being exceeded: in practice, if the voltage is too high (> 16.5 ± 0.5 V) or if the voltage is too low (< 7 ± 0.5 V) this

causes the alternator to work irregularly in both cases with a consequent instruction by the NBC to light up the warning light in the instrument panel.

If recharging signals are not present or irregular, carry out the following checks before dismantling the alternator:

• check belt tension;
• check the nut on the positive alternator terminal (B+) is tight and ensure the washer is present;
• check the nut on the excitation terminal (D+) is tight and ensure the washer is present;
• check that the nuts on the positive junction unit in the engine bay are tight;
• check the bolts securing the negative terminal to the body are tight;
• check the battery terminals are clean and fully tight;

NOTE:

If the Body Computer does not provide the energizing signal, the alternator is energized at 1000 engine rpm (about 2200 alternator rpm) exploiting the residual magnetic field.