Alternator/regulator problem? - K-Bikes.com - Excellence in Motion
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post #1 of 15 (permalink) Old Dec 21st, 2005, 9:28 pm Thread Starter
 
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Alternator/regulator problem?

Greetings. My 98 (119,000 miles) has recently developed strange electrical problems.
The battery ran down because, I suspect, the alternator/regulator is intermittent. When
I also noticed the battery charge light on the dash wasnt coming on with all the others
with the key on (motor not running), I pulled the bulb but it was good (I tested it). So
what happens now (battery fully charged and its only 9 months old) I see 12.5 V. When
I turn the key it drops to 12.1V (ok so far) then after starting the bike I see 11.5V (not
good). However reving the motor will eventually cause the voltage to jump to 14.5V and
stay then stay there while idling. I havent ridden the bike so I dont know how long it
maintains 14V+. The dash light thing though makes me think the regulator/diodes
are bad. The schematic shows the dash lights all on the same ground and the hot side
of the charge lamp goes right to the alternator.

A regulator/brush unit is only $100 but according the service manual you have to remove
the tranny and rear end then lift the frame to gain access to the damn altrernator.
Bummer!

Im very interested in any comments.

Thanks, Tim
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post #2 of 15 (permalink) Old Dec 21st, 2005, 10:13 pm
 
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Smile Alternator

Tim
The brushes are probably shot. If you got over 100K out of them you did good.
They can be replaced but you are probably better to replace the whole regulator. The reg .is the same as the car reg. and available all over. Check Google.
Do not buy any but Bosche. I never replaced mine on the K12 but did on my K100. Just 2 screws. easy job if you can get at it.
H
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post #3 of 15 (permalink) Old Dec 22nd, 2005, 4:25 am
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Agree with HGP3. As the alternator brushes wear down shorter they make intermittent contact with the rotating sliprings so you get intermittent output, depending on when you hit the next bump in the road.

I'm not familiar with this setup, but if the regulator is separate, I'd sort the brushes first, but check for wear/scoring on the slip rings they press against. Sometimes an electronic component that's been working reliably is best left if it's ok. But then for most of us, fault finding an alternator can be difficult because you don't know if it's windings, rectifier stack, or regulator. My local auto shop can test most alternators.



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post #4 of 15 (permalink) Old Dec 22nd, 2005, 6:55 am Thread Starter
 
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I can believe the brushes are worn out but it doesnt explain why the dash battery
charge light is inop at all times (even during the key-on light test).

Thanks.
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post #5 of 15 (permalink) Old Dec 22nd, 2005, 7:35 am
 
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Quote:
Originally Posted by tmoore
I can believe the brushes are worn out but it doesnt explain why the dash battery
charge light is inop at all times (even during the key-on light test).

Thanks.
My wife's bike had an charging problem with exactly the same symptoms as what you describe. Turned out to be a loose battery connection - we both felt pretty dumb. Worth checking.
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post #6 of 15 (permalink) Old Dec 22nd, 2005, 8:29 am Thread Starter
 
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Thanks but Ive been down that road myself too! That was the 1st thing I checked.

Tim
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post #7 of 15 (permalink) Old Dec 22nd, 2005, 11:09 am
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Charge lights are often driven from one winding of the alternator, then turned upside down in voltage by the regulator or instrument panel after detecting a voltage threshold level. No lamp lit (assuming bulb AND wiring ok) usually means no alternator output, a diode stack or regulator faulty.

If the battery connection has been intermittent for a while, this can cause failure of the regulator.

With 100K on an alternator, I'd pull it and check what we said. You can't afford to have an unreliable alternator on these bikes. It's a tow job once the battery runs out. Since you only want to do the job once, you must be certain the alternator you put back is a goer. If BMW stuff wasn't so damn expensive I'd consider exchanging the alternator for a used one off a lower mileage bike or a full serviced one. Not only would you get new brushes, but probably bearings, slip rings, balance and full electrical checks. Alternators can run up to 12,000 rpm!

You could also make a second check putting an ammeter ( at least 30 A) in line with the battery lead but shunt it to start the bike, turn all the lights on and see if it balances the discharge at 3-4K rpm. Because the charge light comes off a separate circuit, you are confirming that the alternator has little or no output. If the charge is balancing the discharge, your problem is in the indication wiring or circuitry.

NEVER run the alternator with the battery leads or ammeter disconnected. You have a 50/50 chance of damaging the regulator, it's also a good idea NOT to hotwire from a cage to start the bike for the same reason. Often you do one or both of these things ending up with more than one component failure in the alternator system.

It's common for regulators to delay and soft charge after first starting to prevent stalling a cold motor on choke.



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post #8 of 15 (permalink) Old Dec 22nd, 2005, 12:13 pm Thread Starter
 
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Regulator

Thanks Voxmagna,

Some good info there. Ive ordered a new regulator ($107) which contains the brushes
and diode stuff. If I end up needing a new alternator thats a seperate part ($500 new).
The trick will be getting it in the alternator without taking half the bike apart. Since the
alternator cover is plastic, Im considering cutting part of it away. The regulator is only
two screws and pull out/drop in.

But before I act Ill try and locate the wire at the alternator that runs to the dash light
and ohm it. Getting to it will be the problem. The schematic shows the bulb wire has
its own lead off the alternator.

My other idea was to wire the volt meter up and go for a ride and see whats going on.
My assumpioion is that anything over 12.5V means the alternator is driving. That 14.5V
I see after startup means something is going on but it may be intermittent.

Ill give that ammeter idea some thought as well.

Happy Holidays to All!
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post #9 of 15 (permalink) Old Dec 22nd, 2005, 2:32 pm
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Tim
My manual for the later KRS says you can replace the regulator/brushes WITHOUT removing the alternator.
Remove the three screws on the rear of the plastic cover. On the side, rearward surface of the plastic cover unlock 3 clips which are outboard and in line with the screws, take off plastic housing.
Remove 2 screws on the voltage regulator/brush holder and the assembly comes out in your hand.
Good luck
Bruce C
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post #10 of 15 (permalink) Old Dec 22nd, 2005, 2:37 pm Thread Starter
 
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Alternator

Thanks Bruce,

I saw that too but what they mean is you dont have to remove the alternator from
the motor. BUT you still have to gain access to the back of the alternator. Ive been
looking in there with a flashlight and theres only 1/4 inch between the back of the
alternator and the cross brace of the frame. You cant get to the bottom screw of the
3 and if you did you still cant remove the cover. Its a PITA for sure.

Tim
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