Checking the Installed Alternator

GENERAL INFORMATION

During normal driving the charge warning lamp must go out. Otherwise, the fault lies in the alternator or voltage regulator. First, check the electrical connections of the alternator. Check that the drive belt is correctly tensioned. Further testing can only be carried out on the removed alternator; however, first check all fuses.

Checking the Voltage Regulator

PROCEDURE

1. Connect a voltmeter between the positive and negative terminals of the battery.

2. Start the engine. During starting the voltage may drop to 8 V (at an outside temperature of +20°C).

3. Increase the engine speed to 3000 rpm. The voltage must then be between 13.5 and 14.5 V. This indicates that the alternator and regulator are serviceable. The alternator output voltage (system voltage) must be higher than the battery voltage so that the battery is charged during driving.

4. Check the stability of the voltage regulator. To do this, switch on the high beam and repeat the measurements at 3000 rpm. The measured voltage must not be more than 0.4 V higher than the previously measured value.

5. If the voltage does not correspond to the specified values, the cause may be worn alternator brushes, weak brush springs, a faulty voltage regulator, a faulty diode, an open circuit in the stator winding or defective rotor slip rings.