Sttor coating?

[mf70]

Well, I've got the new copper back on the stator frame.

The next challenge is the coating. Washington DC has no rewind shops that will talk to civilians, so I'm back here...

What function does the coating serve? I always thought vqarnishing or epoxying an armature helped strengthen it for high RPM, but that can't matter here. Since it IS a stator, it doesn't move much. Does it help to transmit heat from the coils?

The recommended 3M epoxy was $35 for two ounces from McMaster-Carr.

Would plain old varnish, dried hard in an oven, do as well? What about leaving it uncoated? There are a couple of threads from 2005 and 2003 that mention this. How have they held up?

I might oven-test some laminating epoxy to see if it will survive 500F. It doesn't have to be very strong at that heat; it just needs to not burn.

There's no doubt the original stator got plenty hot - the leads going to it were cooked black and brittle for the last four inches of the wire loom - the part that's led down along the case under the wire cover.

MarkF

[Steve]

Hopefully, there is some coating already on your copper. :shock:

If you used BARE copper wire, all your effort has been in vain.

The normal coating on the stator windings is a clear insulator, but it is on the wire before it's wound. If you have used bare wire, you will have less output than if you had put just one turn on each pole.


.

[mf70]

Thanks for your prompt reply.

Yes it's magnet wire.

The questions still stand: What function does the epoxy top coat serve on a (static) stator: cooling or some kind of mechanical backup, and what is the experience of those guys that did without three years ago.

MF

[Steve]

I can't imagine how it would work to dissapate any heat. If anything, it would increase the thermal mass, holding heat in. My guess is that it is to mechanically stabilize the windings.


.

[Red Rocket GS1100]

See I thought....

I thought the coating was to keep it ( the windings ) from corroding. The electrolysis action involved causes ionic transfer which leads to corrosion. The same electrolytic action happens in dissimilar metal contact. The difference here is that the metals dont actually touch but the ionic transfer still occurs.
It's probably way wrong...just some left-over information from science class and a bit from being a electro-plating guy in the past.

[mf70]

Hmmm. Electrolysis in an oil bath. I don't think so. Electrolysis IS a big problem, but only where water/salt can get to the joint.

I can imagine:

1) vibration causing the wires to chafe against each other and short.

2) poor cooling due to air gaps inside windings.

3) poor cooling due to dirt accumulating inside windings.

Several folks reported in 2005 that they had replaced the stator "naked," using only the coating on the wire as insulation. I'd be interested in hearing how their stators held up.

[twistedwankel]

Well, I've got the new copper back on the stator frame.


What function does the coating serve? I always thought vqarnishing or epoxying an armature helped strengthen it for high RPM, but that can't matter here. Since it IS a stator, it doesn't move much. Does it help to transmit heat from the coils?

The recommended 3M epoxy was $35 for two ounces from McMaster-Carr.

Would plain old varnish, dried hard in an oven, do as well? What about leaving it uncoated? MarkF

Find an industrial electrician who has access to a Megger. This tests the integrity of your insulation non-destructively. The higher the ohms the better initially. The less the goop the better the heat transfer with the hot oil flying around in there and no air.

That should tell you if you can go with what you have. It is common practice to bake out the windings on old working motors and then soak and rebake with new liquid insulation but that will end up costing you more than just buying a new Stator? You need something that works in a sealed motor design - higher temp resistance. Hopefully your modern wire is that level of heat resistance.

[suzuki-newfie]

MF70,

I'm just re-building my stator and am in the same boat as you with respect to epoxy. Personally I don't think there's any risk to the assembly by not using epoxy. I think it will actually provide better cooling for the stator.

One problem I did run into is that I couldn't get enough windings with the 17ga magnet wire. The original had 32 windings on each post, but I was only able to get about 25 per post. If the voltage output of a brand new stator is 75V, then mine should be 58V based on Faraday's law. I don't know if it's going to be enough.

What size wire did you use and were you able to get the right number of windings?

Craig

[twistedwankel]

MF70,

If the voltage output of a brand new stator is 75V, then mine should be 58V based on Faraday's law. I don't know if it's going to be enough.

Craig

I put a used stator on my bike recently and it only puts out 60VAC per leg but still puts a strong 14+VDC out of the rectifier. Go figure? It looked much cleaner (brighter) than the original so maybe it had been rewound??

[robertbarr]

MF70,

I'm just re-building my stator and am in the same boat as you with respect to epoxy.

I think it's a pretty cool trend to see people winding their own coils. You folks be sure to let us know how it turns out. I've also been watching the homebrew open-source R/R thread:

http://www.thegsresources.com/_forum/showthread.php?t=94447

(Not quite finished, but it's interesting...).

[suzuki-newfie]

I finished my stator tonight I have to say I'm a little encouraged by some of the posts I've read. I have 0.4ohms of resistance across each set of windings (note that I used the Y-circuit three phase generator).

I did find a product that I'm trying out as a coating for the stator. It's Permatex Aviation Form-A-Gasket. The stuff looks identical to the original epoxy on the stator, it's applied with a brush applicator, is good up to 400degF and resists gas and oil. It's actually the stuff that I normally use to seal my crank case on engine rebuilds. Here's the link for it - you should be able to find it in any automotive store and its only $4.

http://www.permatex.com/products/automotive/automotive_gasketing/gasket_sealants/auto_Permatex_Aviation_Form-A-Gasket_No_3_Sealant_a.htm

I also joined the leads to the magnet wire, and covered them with shrink tube (despite recommendations not to). The shrink tube is rated to 257degF and I covered it with the permatex as well.8-[

Now for the final test tomorrow when I put it back on the bike. I had 24V on each set of windings before I started the job.

If anyone else has any experience with the number of windings you were able to achieve using the Electrex recommended 17ga magnet wire I'd appreciate any learnings. In hind sight I wish I had used 18ga wire. We'll see if it works tomorrow.[-o<

Craig

[Nerobro]

coatings would only help for one thing.. making sure your windings dont' come lose. otherwise it will only add insulation, and that is something we definitely do not want on our stators. I could see putting a bead of epoxy down the face of each winding to secure the windings.. But anything beyond that I can't recomend, and it would prevent you from rewinding the stator in the future.

I have rewound a stator... I'm looking at 3000 miles on this one :-)

As far as I can tell, there is no epoxy on the factory stators. Other than on the core itself. The "epoxy" you see is burnt insulation and cooked oil/sludge.

[Lonthemon]

could this keep the stator cool?

I rewound my stator and it burned up in 3000 kilometers. I used JB Weld as a coating. For my next attempt, rather than using a shunt regulator I am using a "series" regulator from an alternative energy site.

http://www.fourwinds-ii.com/v2/?c=flexcharge&i=006

I believe this regulator will stop the stator from getting hot and from eventually burning up. My only kicker is that I Have to use a separate rectifier (buildable for 10 bucks). In the end my stator should only pass the current the bike need. No more shorting of excess. No more unnecessary stator current. No more replacement of stators! I hope.

[mf70]

MF70,

I'm just re-building my stator and am in the same boat as you with respect to epoxy. Personally I don't think there's any risk to the assembly by not using epoxy. I think it will actually provide better cooling for the stator.

I got a response on the EV discussion list from a Jeff Major:

Even though it is a stator, not rotating, the wires may move with the magnetic forces, so it should be"varnished". I'd suggest a polyester or epoxy resin made for this purpose. Dipped and baked. Maybe twice. Some places will even vacuum impregnate to suck the stuff up into the slots.We did some work on oil cooled stators and found some materials will dissolve in the hot oil, some did not. You might want to make a test batch before dipping the real thing.Supplier---EIS, Electrical Insulation Suppliers, Inc.,Atlanta, GA, 404-355-1651 Sorry, I don't remember the product name we went with. Jeff

He sounds like someone that knows...

One problem I did run into is that I couldn't get enough windings with the 17ga magnet wire. The original had 32 windings on each post, but I was only able to get about 25 per post. If the voltage output of a brand new stator is 75V, then mine should be 58V based on Faraday's law. I don't know if it's going to be enough.

What size wire did you use and were you able to get the right number of windings?

Craig

I took the stator to a place in Southern MD, and after they got finished laughing and saying they wouldn't rewind it, they chose the wire and eyeballed the amount needed. I measured it with a micrometer, and it was near #18. They were right on the money as to length.

I got within one turn of "spec." I used a home-made tensioner made of two pieces of oak with a gentle serpentine path for the wire. It straightened and applied tension to the wire. I was then religious about laying the turns beside each other. I was able to keep them pretty tight until the third layer.

For insulation, I bought a yard of high temp #12 wire. It was open stock at the local hardware store. It had a fiberglass outer sheath and a silicone inner sheath. I led the magnet wire, inside silicone "noodles," up away from the stator (the original wire leads had been spliced to the windings at the stator, and had cooked black and brittle to 4" from the stator, even inside the outer cover and behind the long wire guard), and used the fiberglass sheath to insulate the 3-way splice. I'll use crimp barrels (without plastic cover) for the wire joins.

I've got a test coil coated with plain wood varnish that I've cooked in an oven for a couple of hours. It looked pretty good. Jeff's note gives me the idea to test cook it in a deep fat cooker. That should get above the temp. for working engine oil!

That said, I think I'll try again to track down the "real deal." The JBWeld is an interesting idea, but I'd like to penetrate the turns as much as possible, and I'm not sure what the conductive iron filling in the JBWeld would do. (I used it to secure poles in a permanent magnet motor once, and it flowed in the magnetic field - spooky.)

Nerobro: As far as I can tell, there is no epoxy on the factory stators. Other than on the core itself. The "epoxy" you see is burnt insulation and cooked oil/sludge.

I'm pretty sure I saw two kinds of flakes from the wire as I stripped it from the form, the light even varnish that had insulated the wire, and heavier spears of resin that acted like slivers. I'm pretty sure Jeff Major describes standard practice.

MarkF

[suzuki-newfie]

Success!

Hi All,

I finally got my re-wound stator back on the bike and it worked just as Michael Faraday predicted. I got between 55 and 60 volts across all three sets of leads, which is consistent with the calculation I showed earlier. The 17 gauge wire worked well. I had no issues on startup and now I'm getting between 14 and 15V on the battery at 5000rpm. The battery was too weak to roll the engine but after about 10 minutes of engine running it was able to start itself.

In summary, here's the job:
- Unwind old stator.
- Re-wind stator with 17ga wire - could only get 25 new wraps versus 32 wraps originally on each post.
- Made connections and covered with shrink wrap good to 160degC.
- Coated stator with permatex form-a-gasket.
- let dry for 2 days.
- re-install on bike.
- ride (finally).

Craig\\/