Engine
SHOP MANUAL
Ch 1 page 163
Alternator 100 A
When the engine control unit has generated fault codes for the alternator, the following tests can be carried out.
• Output test
• Control voltage test
• Phase measurement
• Length of brushes
• Slip rings, rotor resistance and overcharging
Test Test values Mea-
sured
values
Acceptable
value
Incorrect
value
1. Output test Bosch 100A:
>40A and 28V
Carry out volt-
age test
Carry out phase
measurement
Control voltage test 28 +/- 1.0V at 20°C Alternator OK Check the brush
length
Phase measurement <250 mV Check the
brush length
Renew alternator
Brush length¹ Bosch 100A:
>1.0 mm
Check slip
rings
Renew alternator
Slip rings¹ The surface should
be smooth and bright
Check the ro-
tor resistance
Renew alternator
Rotor resistance be-
tween the slip rings (at
20°C)¹
Bosch 100A:
8.5 +/-0.5 ohms
Carry out over-
charging test
Renew alternator
Measuring overcharg-
ing between slip rings
and framework¹
> 10 MOhm Renew regula-
tor
Renew alternator
Check
Make sure that you never run an alternator without the batteries
connected! This may cause the rectiers and/or charge regula-
tor to be overloaded and damaged.
To obtain a correct result, the alternator should be kept at a
temperature of 20-25°C. A higher temperature may give a lower
current.
NOTE
CAUTION
Figure 318
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