Stator r/r Nightmare - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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Where does this wire go?
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post #1 of 21 (permalink) Old 05-31-2019, 09:03 PM Thread Starter
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Stator r/r Nightmare

So I joined the stator burnt up club. I bought this bike a short time ago it’s a 98 and someone before me did the tuxedo mod. It wouldn’t charge at all and I decided to replace to stator and the reg rec and a new battery. I put new parts in put about 50 miles on it and got home noticed that the wires on my new rectifier the dc side were slightly melted. I checked it all over and I the stator seemed to be fine but my voltages were all over so I emailed the company “Caltic” android hey said huh and sent me a new one I put the new on in and same problem. When I have the ac side plugged in, guy before me removed the mollex connecter, and the dc side out I’m fine go to plug the dc side in so it’ll charge and starts trying to melt the ac side wires. I need some help as to what to check. It can’t possibly be stator bad already, can it?
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post #2 of 21 (permalink) Old 05-31-2019, 11:00 PM
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I think I’m following you here, but the DC side is technically the output of the R/R isn’t it? If the stator output on it own is good I wouldn’t think that was the issue. Especially getting the same result from two stators.
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post #3 of 21 (permalink) Old 06-01-2019, 04:44 AM
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Which type of regulator did you get? Does it use mosfets or thyristors?

Do you have the proper amperage fuses in your fuse box? (i.e. no 50amp fuses in a 5amp slot? Sometimes people 'beef up' the fuse in a circuit that keeps blowing, masking the true problem and allowing a short to burn up wires)

When exactly do wires start to overheat?
Plugging in the DC side with the ignition off?
Turning the ignition on but not starting the bike?
Running the engine at idle?
Running the engine above idle?

1992 US-nonCA * tuxedo mod * r/r relocated

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post #4 of 21 (permalink) Old 06-01-2019, 11:05 PM
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The stator puts out AC, at full blast over 3000 RPM. That goes to the R/R, which does two things. It converts the A/C to DC, and it shorts excess current to ground. Make sure the R/R is properly grounded. I've never heard of this problem with a Vulcan before, but I had an '85 Goldwing that actually caught on fire. The R/R could not handle the stator output, got really hot, and set the wires and plastic connector connected to it on fire. These bikes use a Model T charging system. I keep hearing about MOSFET R/Rs, but I've put close to 190,000 miles on 2 Vulcan 750s, and never did replace an R/R. I did have to replace one stator. It was burned to a crisp. I recently bought a 1997 Vulcan with 21,000 miles on it. Before buying it I checked to see if it was charging, and I removed the 3 screw cover to make sure nobody had done any cutting or drilling in there.

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1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #5 of 21 (permalink) Old 06-02-2019, 04:00 AM
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I'm guessing these stators are wound in the wye configuration. Anyone know if the center is electrically connected to the frame of the bike? Like, is the neutral of the 3-phase the same as the ground of the DC? I would have thought not, but ... ?

1992 US-nonCA * tuxedo mod * r/r relocated

Vulcan slang for newcomers
Service Manual Download
Wiring Diagram + annotations * still undergoing revisions, but still more useful than the generic one. Let me know if you find mistakes or think something additional should be added
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post #6 of 21 (permalink) Old 06-02-2019, 09:07 AM
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Electrically speaking I don’t think that neutral is shared at the stator to the frame. That would be the same as a path to ground. Which is a good indicator of a dead stator. It’s been a while since I dug into electrical theory but grounding happens post AC to DC conversion starting at the R/R ( heat output from the regulator) when it “dumps” unused current and any other circuit post that point has a ground.
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post #7 of 21 (permalink) Old 06-02-2019, 10:13 AM
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There is no ground or center connection for the stator windings.

The R/R does not short the excess output to ground, it shorts the stator winding outputs to each other. That high current in the stator windings causes a magnetic field that partially opposes the magnets in the rotor reducing the power generated. It also generates heat in the windings which should get passed on to the engine oil in which the rotor is bathed and the engine parts to which it is bolted.

I have a theory thats it is poor R/R's that cause most stator failures. A modern MOSFET design runs cooler than the SCR based older designs so will be generally more reliable. The MOSFETs have different switching (and failure) mechanism than the SCR and are less likely to stick ON.

I killed my original R/R by installing LED lighting. The bike took less power so the R/R had to work harder. Replaced with a MOSFET and no more problems. But i could easily have joined the stator faliure club had I not seen charging issues with the voltmeter and gone looking. It still killed a battery before i could get to it as the AC power was getting past the R/R to the battery terminals and the bike.

To an Ohmmeter the stator looks like three wires joined at the far end, there should be no path to ground for any of them.
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post #8 of 21 (permalink) Old 06-02-2019, 11:08 AM
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You can quit putting stators in until you find what’s killing them. These are not engineering complicated issues, they are simple units. With both stators eliminated as the cause put a good RR in there. At this stage you should test for amperage at each point and see where it’s headed if you’d like to troubleshoot it, but a good RR would solve it.


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post #9 of 21 (permalink) Old 06-02-2019, 11:35 AM
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The R/R DOES short a percentage of power to ground, it converts it to heat. For more detail you can read this

https://www.electrosport.com/pages/t...g-system-works

Moral of the story though it sounds like the R/R is probably your issue
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post #10 of 21 (permalink) Old 06-02-2019, 11:55 AM
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The R/R on my Goldwing (the only one that I ever had a problem with) shorted all excess current to ground. The schematic clearly showed that. Or maybe a more accurate way to put it is that the regulator, which is connected to ground on one side, is designed to absorb the excess current and convert it to heat. The regulator part is just a resistor, designed to convert excess current into heat. That is why it is in a heat sink. It is designed to get hot. Very primitive way to do it. On cars the field output of the alternator is controlled by the load placed on it. 1988 and up Goldwings also do it that way. I don't know of any other bikes that do. Even BMWs have a setup just like the Vulcan. To me it does not make sense to generate too much current, then deliberately turn the excess into heat.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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