The "Why" of Stator Failure? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Electrical
Where does this wire go?
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post #1 of 13 (permalink) Old 06-14-2019, 09:07 AM Thread Starter
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Lightbulb The "Why" of Stator Failure?

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.

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post #2 of 13 (permalink) Old 06-14-2019, 11:06 AM
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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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post #3 of 13 (permalink) Old 06-14-2019, 12:02 PM
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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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post #4 of 13 (permalink) Old 06-14-2019, 12:04 PM
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Now that Tim Parrott's gone, you may be best off with a new OEM unit.
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post #5 of 13 (permalink) Old 06-14-2019, 12:21 PM Thread Starter
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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...-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-inf...ence-Chart.asp

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

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf

Last edited by Spockster; 06-14-2019 at 12:35 PM.
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post #6 of 13 (permalink) Old 06-14-2019, 01:23 PM
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Quote:
Originally Posted by calebj View Post
Now that Tim Parrott's gone, you may be best off with a new OEM unit.
.

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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post #7 of 13 (permalink) Old 06-14-2019, 01:59 PM
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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.

TOC MCCTs
Saddlebags, hard mounted
Fork mounted tool bag (now hard mounted)
Relocated rear turn signals
LED turn signals, brake lights and running lights
LED license plate frame
Engine Guard and Highway pegs
National Cycles Low Boy Heavy Duty windshield
Home made lowers (nice)
Custom seat (made by a local guy)
Iridium plugs (DPR7EIX-9)
Shenko 230 Tour Master tires at 11,123 miles
Splines lubed at 11,123 miles
Luggage rack
Light bar with LED lights
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post #8 of 13 (permalink) Old 06-14-2019, 08:42 PM
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post #9 of 13 (permalink) Old 06-14-2019, 10:26 PM
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Quote:
Originally Posted by Chris and Shim View Post
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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post #10 of 13 (permalink) Old 06-14-2019, 10:57 PM
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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.

TOC MCCTs
Saddlebags, hard mounted
Fork mounted tool bag (now hard mounted)
Relocated rear turn signals
LED turn signals, brake lights and running lights
LED license plate frame
Engine Guard and Highway pegs
National Cycles Low Boy Heavy Duty windshield
Home made lowers (nice)
Custom seat (made by a local guy)
Iridium plugs (DPR7EIX-9)
Shenko 230 Tour Master tires at 11,123 miles
Splines lubed at 11,123 miles
Luggage rack
Light bar with LED lights
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