Sounds like it is not charging at all. If you test on AC Volts on the 3 wires coming from the alternator you should get the same voltage between any two wires of the 3. Not sure what they will be on a BMW but would guess between 60 to 90 volts. Are you going to replace the regulator as well?
Charging Light Troubleshooting
- Thread starter DCoplin
- Start date
DCoplin
Registered user
Just a quick update on progress:
1) New diode board confirmed it wasn't the diode board. On the bright side, I now have a spare for next time.
2) I discovered the "diode mode" on my multimeter (thanks @Strongbow92 !) - which also confirmed it wasn't the diode board (d'oh!).
3) Tested the Stator and continuity and resistance was as it should be.
4) Removed rotor and confirmed resistance between the rings is 0.8 Ohms - so bugger me, it was the rotor all along.
So far I have learnt:
1) Multimeters do more than check voltage and continuity.
2) Simply wishing that the problem is the easiest component to replace (first regulator then diode board) is a poor substitute for actual proper testing
.
3) This forum is freakin' awesome (and has been for over 20 years!).
Replacement rotor on order, will report back on progress.
Have a great weekend all!
1) New diode board confirmed it wasn't the diode board. On the bright side, I now have a spare for next time.
2) I discovered the "diode mode" on my multimeter (thanks @Strongbow92 !) - which also confirmed it wasn't the diode board (d'oh!).
3) Tested the Stator and continuity and resistance was as it should be.
4) Removed rotor and confirmed resistance between the rings is 0.8 Ohms - so bugger me, it was the rotor all along.
So far I have learnt:
1) Multimeters do more than check voltage and continuity.
2) Simply wishing that the problem is the easiest component to replace (first regulator then diode board) is a poor substitute for actual proper testing
.3) This forum is freakin' awesome (and has been for over 20 years!).
Replacement rotor on order, will report back on progress.
Have a great weekend all!
I take it you have read this.
bmwmotorcycletech.info
Sent from my backyard
BMW Airhead Motorcycle Alternator troubleshooting and Repair
BMW Airhead alternator system repair
Sent from my backyard
Unusual for a rotor to go short circuit but still have some resistance.
DCoplin
Registered user
Just to close off this thread - it was the rotor all along. Put a new one in and everything is just as it should be.
Thanks all - brilliant to have your help with this!
Thanks all - brilliant to have your help with this!
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