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Discussion Starter #1
Hypothesis:

If the current from the stator has nowhere to go, such as with R/R or JB failure, excess heat in the stator is produced in a very short time.

Some machines are wired with the R/R going through the CDI. If the R/R fails or is unplugged, the engine doesn't run. Obviously, the VN750 isn't one of those.

Eddy currents are nuts, try dropping a magnet through a copper pipe! It defies gravity! Just a 1/2" water pipe and weak magnet will do, but the stronger the magnet, thicker copper, the stronger the effect. Quite a few of the videos out there. I've tried it myself.

Eddy Current Heat


Gravity Defying!

 

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NewB to Vulcans
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From a EE.

When the the R/R shorts the windings together some of that that energy goes to create a magnetic field that opposes the field of the fixed magnets in the rotor thus reducing the total energy generated. Some of that energy however turns to heat in the wire.

The stator wires are covered in a very thin insulation coating so that more wires can be wound on. They are wound around iron cores stamped out of sheet steel (with sharp edges) so the windings are square not circular. As the copper heat up and cools down it stretches and shrinks at a different rate than the iron it is wound on so there is some rubbing which will concentrate on the corners even though the whole assembly is coated in an epoxy or similar encapsulant.

As soon as a corner gets worn down to the point that the wires touch it is all over. Once you have a single "shorted turn" like that all the energy goes to that one loop causing the wire to heat up like a stove top, shorting other turns together and propagating until that section of the stator blows like a fuse. Hence the pictures of just one section burned up on the failed stators with adjacent sections showing some signs of heating.

Transformers do the same thing when they overheat. The big power ones on poles go off like fireworks if a lightning strike's high voltage causes the insulation to fail, big purple flash and a shower of sparks.

Better quality insulation, careful winding and good protection of the iron core all help.

I suspect the original stators were built to a certain quality level that balanced cost and performance. I also suspect the replacements out there are built to an even lower price, this would explain the serial stator failures after a replacement. In a competitive market you can generally assume you get what you pay for, a lower price means they cut a corner somewhere. Likely they used thinner, lower temperature or poor quality insulation on their wires which is nearly impossible to detect and wont show up immediately in use.

The R/R has a lot to do with this too, my original failed short circuit completely, it was letting AC get to the battery and DC get to the stator, neither of which are good as it causes more destruction. Again they are designed to a price and to last as long as the warranty. A modern MOSFET R/R has very different failure modes as well as reduced power dissipation so is better all round.

There is nothing fundamentally wrong with the design, its crude but effective. If Ma KAW held their suppliers to a slightly higher standard or made the stator easily changeable we would not be having this discussion. As it is you have a weaker then normal component that is not easy to replace, gives us something to talk about.
 

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Retired USAF (IYAAYAS)
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So, setting aside the PITA of actually changing the stator out, what combination of replacement parts would constitute a very good-to-best quality electrical system? MOSFET RRs come to mind. But what replacement stators are thought to be best quality? (Money not being an issue.)
 
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Now that Tim Parrott's gone, you may be best off with a new OEM unit.
 
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Discussion Starter #5 (Edited)
Two companies I had previously posted, don't seem to be doing rewinds any longer. Willyscycle and Cycletronics, sister companies in Alabama.

A quick search turns up this one, recommended by some popular forums: https://www.bajadesigns.com/products/Stator-Rewinding.asp Looks like $175-200.

Edit: They don't list our 750, but their chart shows substantial output increases: https://www.bajadesigns.com/tech-info/Stator-Reference-Chart.asp

Someone here did the electrical mods and got a Rick's to survive.
 

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Now that Tim Parrott's gone, you may be best off with a new OEM unit.
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My stator is currently being replaced, not having a good place to work on my bike I had to get someone to do it. I shopped around for a bit and the response was pretty unanimous about using OEM replacements (especially the stator). I figure I can afford this repair once and once only, if it goes again you’ll see me posting that I’m selling parts because I’ll be looking for a different bike. I’m too hesitant to cut the engine case. If I had a garage and a couple bikes maybe I’d think differently.
 

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Retired USAF (IYAAYAS)
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I'm the same way. I love this bike like no tomorrow. I'd do a single stator replacement (right now its fine) but after that if it fails again I'll part mine out as well.
 

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I'm the same way. I love this bike like no tomorrow. I'd do a single stator replacement (right now its fine) but after that if it fails again I'll part mine out as well.
I’m hoping I don’t have to come to that decision to part it out or sell it. I got the bike last year with 18k on it and I just passed 20k before it crapped out. 20k miles seems too soon for a failure, but again if it’s the original it’s 14+ years old. Time will tell. Right now I just want to get that call from the shop that it’s done so I can ride, I’m getting antsy
 

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Retired USAF (IYAAYAS)
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I'm the original owner for mine. Its at about 15.5K miles. This thing fits me like a glove. I don't want to change gloves.
 

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It’s my first bike, so I don’t have anything to compare it to but I sure know I’ve been having a great time with it. Im not done with her yet
 

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Discussion Starter #12
Check Roadster Cycle,California??
Got my MOSFET from him, but he doesn't do stators. Has series type r/r kits also.

He's updated his page a bit, I noticed he says the MOSFET is OEM for some Yamaha and Suzuki bikes. Says he'll give tech support even if you bought your r/r somewhere else, and tells you how to spot the fake MOSFETs being sold cheap.

https://roadstercycle.com/
 

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Over the winter, I'm dropping my engine for a coolant leak.
While I'm at it, I'm considering the tuxedo mod, since the engine will already be out.
So far at 27k miles, the stator is still good.

If the suspected failure mode is thermal expansion wearing away the insulation, is it possible to recoat it before it fails?
I'm thinking of anything from spraying it with lacquer, to brushing on clear fingernail polish, to dropping the entire stator in a bucket of lacquer.
Since it's in the inside corners of the windings, it's probably going to take soaking it.

Next question is if it would be worth it.
It might take $$$ worth of lacquer just to have enough to submerse it.
 

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NewB to Vulcans
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My suspicion is that the wear thru occurs inside the already encapsulated windings. Its going to be really hard to get that stuff off without damage to the wires, i would leave it alone if its working OK
 

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You'd never be able to re-coat it in such a way that you'd be prolonging it's life. The insulation on the wires is super thin and applied to the wire before the winding occurs. The post-wound stator is epoxied after winding to prevent vibration, and that epoxy is probably very much intact when the wire insulation breaks down. Any additional epoxy you add would just trap heat in the stator and wouldn't do anything to prevent a short between the windings.
 

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I'm a rider
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Ricks is the best stator out there. A good stator has to do more than produce electricity. The Caltric stators don’t push until close to 1050rpm, the Ricks start pushing at 750 and are above 13.8 by 850, and peak at 14.4 around 1000. The regulator will start backing it up around 3600. That’s where you start stressing the stator.
 

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Just a lil bit of carb tuning and she’ll hit a lick.

800rpm



Caltric voltage notice how high the rpm is to get above 13


Ricks voltage always 13 + (14.8 at 1100)

 

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I have replaced one stator at about 85,000 miles. I just recently bought a 1997 model with 27,000 miles on it. Right now it is charging fine. But I removed the bullet connectors in the three yellow wires and soldered them anyway, even though they showed no signs of overheating. I doubt I would replace another stator. Some people take shortcuts, I pulled the engine completely out of the bike, which required disassembling a good part of the rest of the bike. It was a 6 month project on and off. It's sad that this simple design flaw (having to remove the engine) has caused so many people so much grief. That and a few other things about the VN750 cause me doubts about the competence of Kawasaki's engineers. The bike would have been just as good without these issues. The VN750 turned out to be a great bike despite it's flaws. But it seems like it was designed by several different people who never communicated with each other.
 
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