Electric Test on Bosch Alternator

NOTE: Alternator disassembled
Make tests with BMW Service Tester.





Checking rotor winding for breaks and shorted turns
Place test lead for resistance testing an slip rings.
Alternator
- 80 A = 2.8 Ohm ± 10 %:
- 65 A = 3.4 Ohm ± 10 %
- 90 A = 2.9 Ohm ± 10 %:
- 115 A = 2.65 Ohm ± 10 %:
- 140 A = 2.65 Ohm ± 10 %:





Checking rotor winding for short circuit to earth
Connect test lead for resistance test on slip ring and rotor shaft.
Specified value: infinity corresponds to display 999 K Ohm.





Checking stator winding for short circuit to earth
Connect test lead for resistance test on solder point and stator (winding carrier).
Specified value: infinity corresponds to display 999 K Ohm.





Checking stator winding for breaks
Compare resistance values of wires 1/2. 1/3 and 2/3 with an ohmmeter - must be identical.
Shorted turn test can be performed with a standard test probe.





Checking negative diodes
Connect test leads for diode test.
Negative lead on cooler and positive lead on one of negative diode connections.
Display with perfect-condition diodes:
polarity "-".





Checking positive diodes
Connect negative lead on B+ connection pin and positive lead on one of positive diode connections.
Display with perfect-condition diodes:
polarity "+".





If a diode is faulty, replace the entire diode plate.