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Old 07-19-2004, 10:40 AM   #1
road2blue OP
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Joined: Apr 2003
Location: Fraser Valley, BC, Canada
Oddometer: 841
Airhead Charging System Puzzle

1993 GSPD with about 85,000 KM (50,000 miles). I just replaced the alternator rotor (for the third time). Prior to and after rotor replacement, I noticed that in the morning I start it up and as I drive the (aftermarket) voltmeter jumps back and forth indicating between 13 and 14.5 volts. It jumps quite a bit which I think is fine - indicates the alternator is putting out power and the regulator cuts in and out as required. After about 10 minutes of riding, the voltmeter needle stabilizes at 13 V. This generally corresponds with my arrival at a freeway on my moring commute. The needle stays pretty much rock solid on my 15 minute highway commute (4500 to 5000 RPM). When I get back into city traffic, stopping for lights,etc, lower RPMs (idle to 4000), the volt meter is indicating only about 11 volts. My total commute time is about 30 -40 minutes. My battery is about 1 yr old and I haven't had a problem with it dying. Could it be a regulator issue that only happens when the bike gets warm? I just added some water to the battery this morning and will keep an eye on it to see if its boiling the acid/water out. My concern is that perhaps my alternator is running full out all the time (once the engine warms up) and that is causing the premature failure of the rotor. I've had the bike since it had about 15,000 km on it (one year old). As stated, I replaced the battery last year (first time) and I've smoked three rotors. Could my regulator or Diode Board be faulty? Currently (pardon the pun), I'm not running any extra electrical stuff (I've got heated grips, vest, radar detector and aux lights but none of these have been switched on since I blew the last rotor and really started paying attention to what is going on). I also haven't done the brushes yet but anticipate updating them before fall/before my next little trip.

Any help appreciated. Thanks.
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Old 07-19-2004, 10:59 AM   #2
Joined: Feb 2002
Location: Flyover State
Oddometer: 32,310
Aren't you supposed to renew the thermal grease on the regulator periodically? I wonder if its not shedding heat correctly and that's causing a problem.

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Old 07-19-2004, 11:21 AM   #3
Found:Gideon's Bible
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Joined: Jul 2001
Location: Collapsed in the Corner
Oddometer: 63,305
Call the guy who runs this website and then order some parts from him.

He nailed a diagnosis for me.
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Old 07-19-2004, 12:10 PM   #4
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Joined: Jul 2004
Location: Richmond, KY Where Bluegrass Kisses the Foothills
Oddometer: 10
Originally Posted by AnnieGS
Good advice, and also spring for his book that explains airhead charging systems.
If you can stand spending the $575.00 for his 400 watt charging system (you get everything new) ( you will probably cure all of your "current" problems and have all new parts related to electrical....and be able to run all the accessories you like forever.

I did it almost 2 yrs ago on my 1990 GSPD and it's the best mod yet! I did a trip to Alaska last summer with heated grips, aux headlamps, GPS, Chatterbox radio, CD/Mp3 player and a 90watt power inverter that runs chargers for digital & video camera batteries and laptop while going down the road (with headlamp on bright ! )

It works great and I've had no problems. Hope this helps!
The Journey is The Thing .... Homer
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Old 07-19-2004, 06:32 PM   #5
Rubbery-Lip Flappin' PHI
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Joined: May 2002
Location: Albuturkey
Oddometer: 1,478
I'd bet on a flakey diode board. The regulator looks at the voltage coming off a second set of diodes that power only the rotor winding (AKA field, via the regulator). If one (or more) of the main diodes is giving up at temperature, you will be undercharging, and the regulator won't compensate, if _it's_ diodes are fine. Could also be RPM related, as the most common failures are mechanical, and the parts can resonate at particular rpms.

I don't have a wiring diagram handy, but my airhead came with one in the owners manual. If you can figure out how to monitor the voltage at the second set of diodes mentioned above (the ones that power the field via the regulator) and if it looks good, then it is the diode board.

Check out the stator windings visually. Stator problems usually show evidence of heat damage to insulation.
Sincerity is the most important thing. Once you learn to fake that, the rest is easy.
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