Self-Study Program

28
Control units
Alternator test
The following tests are necessary for diagnosis of the regulator:
– Rated voltage
–Undervoltage
–Overvoltage
Voltages are ideally measured directly at the alternator connected to B+. If it is not possible to gain access to
the measuring point, the voltage can also be measured at the slave start connectors.
Rated voltage
The alternator regulator must supply at least 14.3 V.
Undervoltage
The alternator voltage should not be less than 13 V. 13 V are still allowable at low speed and when electrical
consumers are active.
Overvoltage
The alternator voltage must not exceed 15.5 V at high speed and when few electrical consumers are active.
The following are indications of a faulty diode in the alternator:
– Alternator makes loud noise.
– Very high ripple content when measuring harmonic content with the DSO.