Kawasaki VN750 Forum banner

1 - 20 of 21 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter #1
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?
 

·
Premium Member
Joined
·
600 Posts
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.
 

·
Registered
Joined
·
1,284 Posts
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?
 

·
Premium Member
Joined
·
3,026 Posts
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.
 

·
Registered
Joined
·
1,284 Posts
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 ... ?
 

·
Premium Member
Joined
·
600 Posts
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.
 

·
NewB to Vulcans
Joined
·
220 Posts
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.
 

·
I'm a rider
Joined
·
964 Posts
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.
 

·
Premium Member
Joined
·
3,026 Posts
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.
 

·
Premium Member
Joined
·
600 Posts
Exactly, it is a primitive way to do it, but a little more aluminum in the heat sink and it probably wouldn’t be an issue because it would increase the surface area to dissipate the heat (somebody took an engineering short cut). Resistance builds up heat, if you ever replaced a blower motor switch for the heat in your car or truck the plate typically has a different resistors for each position of the mechanical switch basically like a hair dryer. Those coils that heat up are just resistors.
 

·
Registered
Joined
·
1,284 Posts
That's what I thought, TonyO, but wasn't sure since everyone keeps saying the regulator "dumps to ground" instead of "shunts across phases" or whatever the appropriate term would be. Thanks for the clarification that the two systems are not sharing some sort of floating neutral/ground.
 

·
Premium Member
Joined
·
600 Posts
Shunts across phases?? Explain what you mean there. Because the the 3 phases of the stator hit diodes in the rectifier, diodes pass current in one direction only and block the one side of each alternating current coming in, which in electronics is “rectification” then based on load the regulator portion “dumps” unused current to the ground or common. You can call it shunting if you’d like. Anything but “shorting” to ground works.
 

·
Registered
Joined
·
1,284 Posts
Shunts across phases?? Explain what you mean there.

@mmart:
The shunting/dumping happens on the 3 phase side. The R/R detects the ouput voltage on the DC legs, and if the desired output is exceeded, then it causes semiconductors (wired in parallel to the rectifying diodes) between the legs of the 3 phase input to act as resistors, allowing some of the current to flow directly from higher voltage phases to the lower voltage phases (they are neither ground, nor neutral. they are just different phases). This drops the voltage of the waveform being rectified.


Regarding the OP's overheating wires:

The semiconductor (either thyristor or mosfet) doing the shunting generates heat when it acts as a resistor, so R/Rs get hot when the stator is generating more energy than the bike is using. They overheat and blow out when they cannot release enough of that heat to the environment. (Too much current through the resistors, or not enough cooling). Mosfets generate less heat when shunting since they are more 'fast switches' than resistors, so they don't suffer heat-death as easily.

If the R/R is incorrectly sensing too high a voltage, it will effectively drop it's internal resistance to 0, shorting the windings of the stator together, melting the yellow wires, and likely overheats the insulation on the stator windings, leading to a failed/shorted stator.

A R/R can also fail such that a diode can incorrectly pass current in reverse, which is a short between the positive and negative of the battery, melting the DC harness.
 

·
Premium Member
Joined
·
600 Posts
Ah ok, great explanation. Feel like I’m back in tech school. (Scary I remember that stuff). I’m guessing other than seeing the result which is the wires cooked, there’s no real way to test that because mostly everything you mentioned is internal to the RR
 

·
Registered
Joined
·
1,284 Posts
Yes and no ... Using a continuity tester you can check to see if the rectifier is working correctly, but without an electronics testing bench it'd be hard to test the regulator aspect.

You should be able to get current from all stator connections to positive dc pin, but no current from positive dc pin to stator connections. Similarly, you should be able to pass current from the dc negative to all stator connections, but not the reverse.
 

·
Registered
Joined
·
7,942 Posts
Ohm testing for the R/R is in the repair manual.
 

·
Super Moderator
Joined
·
2,570 Posts
MY basic thoughts are if it passes the on bench testing, then the next test that needs to be done is on the bike in operation.

if it fails bench testing, its not gonna pass operational testing (or if it does for some reason 'work', it wont for long)
 
1 - 20 of 21 Posts
Top