1150GS charging problem

[Shaunie]

I've had a problem with the battery warning light coming on intermittently. Thankfully, this has now become permanent as it has given me more of a chance to trace the fault.

While digging around with my multimeter I noticed I had a circuit from the alternator positive to earth, when the ignition is switched on.

Checking the BMW repair manual it mentions, "Checking armature for short to ground - Test with BMW MoDiTec"

Is this referring to the fault I've got and if so, what's the fix? Is it as simple as replacing the alternator, or is there something else I should be aware of?

 

[robc]

What does your alternator belt look like?

Regards

Rob C

 

[beermonster]

Going from memory here, but had same on mine, you may find it's a dodgy connection. There is a small blue wire on the alternator on a spade connector, clean and make sure it's a firm fit.

This the ground for your indicator bulb, when the alternator spins up this wire gets current, therefore cancels the ground and your light goes out.

Simon

 

[MattW]

What does your alternator belt look like?

Flat rubbery thing with lots of small grooves











Sorry - no help at all - couldn't resist

 

[Steptoe]

Going from memory here, but had same on mine, you may find it's a dodgy connection. There is a small blue wire on the alternator on a spade connector, clean and make sure it's a firm fit.

This the ground for your indicator bulb, when the alternator spins up this wire gets current, therefore cancels the ground and your light goes out.

Simon

Post 8 [URL="http://www.ukgser.com/forums/showthread.php?t=261300"]HERE[/URL] same poster same problem

No reply/answer so don't know if the poster has checked and it's ok or hasn't read his own post...... Would help to know and then we'd have an idea what to do next....

 

[Shaunie]

Sorry guys. Yes I have checked the blue wire. There are two of them attached to the same connector. Connection is firm. One of them goes to the instrument panel, which I have checked around the headstock as far as possible, the other I'm not sure where it goes.

If there was a break in this blue wire, would it stop the alternator from charging? When the fault was intermittent, I could see the voltage across the battery changing between 12v & 14v when the light was on or off. Now the light is stuck on and the battery reads 11/12v and then slowly drops.

I have also checked the belt, which looks fine & correct tension.

I did take the alternator to a local auto electrician, who tested it and said it was working, but because the fault was intermittent, now I'm not so sure.

BTW bike is 2001 R1150GS with 32000 miles.

 

[beermonster]

[QUOTE Now the light is stuck on and the battery reads 11/12v and then slowly drops.

[/QUOTE]

Is that reading @ 4000 revs should be around 14v?

 

[Shaunie]

Yep, when I blipped the throttle, the volts would rise.

But not anymore. Now the battery reads 12v upon startup. I've held the throttle with a few revs on (not sure how many exactly) and nothing happens. The bike will run, but the voltage across the battery drops very slowly.

 

[beermonster]

ust seems strange that you got a voltage increase before you took off the alternator to have it checked and now you don't.

The blue wires would not prevent charging, the small one goes to your charge indicator bulb, which is now on, presumably all the time, engine off and on, so that seems fine. Whilst the other goes to the diagnostic plug so should be of no consequence in this scenario.

Are all the connections sound? The large red one from the alternator to your battery and the battery connections themselves, that is tight and clean. Also the alternator grounds through the mounting points are they clean and tight?

Sorry I am not an auto electrician or anything so someone might chime in with a more informed opinion. But if your battery is good and all the above checks out then if you are not getting any voltage increase when you rev the motor with no load on the battery then it seems to point to a faulty alternator. You should get a voltage increase to around 14v when you rev the bike with no load (lights, heated grips on etc) and the voltage should not drop below around 12.6v when you rev the motor with heated grips, lights etc on.

I had a regulator go (it's located in the alternator) and it was a cheap fix, however I think you need to eliminate other stuff first before jumping to any conclusions.


Simon

 

[Stewart H]

I have used a length of wire to prove the alternator or wiring problem before now, just a thin wire from a live to the small alternator tag, and the alternator should start chucking out 13/14 volts with the motor running if its is working

 

[Shaunie]

Thanks Beermonster

The fault was intermittent BEFORE I took the alternator to be checked and was intermittent again for a few weeks after.

If the blue wires wouldn't prevent charging, then I'm edging towards an intermittent fault with the alternator itself, which didn't show up when removed and tested, but has since given up completely.

I can remove it and have it tested again, without to much hassle.

Stewart, to follow your advice, do you mean to connect a live feed to the blue wires, which should turn the warning light off? And check again for 13/14v when running?

 

[Stewart H]

Thanks Beermonster

The fault was intermittent BEFORE I took the alternator to be checked and was intermittent again for a few weeks after.

If the blue wires wouldn't prevent charging, then I'm edging towards an intermittent fault with the alternator itself, which didn't show up when removed and tested, but has since given up completely.

I can remove it and have it tested again, without to much hassle.

Stewart, to follow your advice, do you mean to connect a live feed to the blue wires, which should turn the warning light off? And check again for 13/14v when running?

The current in the blue wires is there to energise the magnets in the alternator, if there is no 12volts there the alternator will not work even with no faults at all, my wire suggestion is to supply an independent 12 volts to prove whether the fault lies in the alternator or the wiring, think of "hotwiring" the alternator. HTH