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Discussion Starter #1
Its an old story. A 98 ZR 600 EFI stator burns the ignition coils. So what!!! Well I decided that I was not going to be content with just getting my stator rewound just like the one that burned up. Obviously there is a problem with these stators because of the number of posts that we all see about them being burned up. Kev and Blaine have begun rewinding them for people with better quality materials but the same gauge wire and that seems to be working for most.

The problem is heat and what Kev and Blaine are doing is using materials with better heat resistance. But where does the heat come from? Obviously the heat comes from a number of sources. The engine gives off heat and also the coils themselves create their own heat because the current they are making has to pass through the coil wires. Not much can be done about the engine's heat other than to do things that others have done like shimming the recoil or drilling holes in the stator housing. these are good things to help, but as I see it the biggest problem is the heat generated by the coil itself.

So how do you reduce the heat from the coil itself? Just like any other current carrying wire, increasing the size of the wire in the coils will increase the amount of current that can be carried, or it will reduce how hot the wire gets if the current doesn't change.

We don't want to change the amount of current that the coils produce so increasing the wire size will reduce the amount of heat produced by the coil. How do we insure that thee same current is produced? Well, the flywheel magnets aren't being changed and the engine rpm range isn't being changed, so from Faraday's law nothing will change if we keep the number of turns of wire the same as the original.

The original high and low speed coils were wound with 36 and 32 gauge wire respectively. The next larger gauge wires would be 34 and 30 gauge respectively. How do you know how much wire was on the original coils. Well we have specs that say the resistance of the original coils is 450 ohms and 45 ohms respectively and the resistance of those gauge wires is 414.8 and 162 ohms per foot respectively. That means there is 1085 and 278 feet of wire on each of the respective coils. Now the larger wire resistance per foot is 261.3 and 103.7 ohms per foot. From that I calculated that the same lengths of the larger wire would have 283 and 28.8 ohms of resistance. Those are the numbers I used ffor my coil rewinds using the larger gauge wire.

The question is whether you can get enough of the larger wire on the spools. Well I wound them tonight and as expected it was no problem to get enough wire on the high speed coil with about 278 feet of wire. The low speed coil with the 1085 feet of wire was the real question. Well I got it wound and it is very close but I made it. Below are some pictures of the wound coils. You can see that the high speed coil wasn't a problem, but the low speed is FAT.

The next step is to install them into the stator and give it a try. I am confident that it will work. In another thread there was some concern that changing the wire gauge would change the impedance of the coil. The impedance will change, but IMO the change due to the resistance of the wire will be small when compared to the impedance from the magnetic inductance of the coil. The later is much more dominant especially in the light of the fact that there are 6 magnets in the flywheel. This means that the frequency of the magnetic flux change will be large and the inductance from magnetic reactance is dependent on this frequency. To shorten this lengthy dissertation, I have considered this and don't feel it is a big concern.

As I said, below are some pictures of the wound coils as well as winding setup I used. Enjoy.
 

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Nice, keep us posted on how it works out in the sled.

Did you varnish the coils after you wound them?
 

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Discussion Starter #4
<div class='quotetop'>QUOTE (mopar4u @ Feb 20 2010, 11:36 PM) <{POST_SNAPBACK}></div>
Nice, keep us posted on how it works out in the sled.

Did you varnish the coils after you wound them?[/b]
Not yet. Actually, I am planning on encasing them in JB-weld epoxy. The specs say that it is good to 600 deg F and doesn't conduct electricity. I will do that once I get them back in the stator and hooked up to the stator harness.
 

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Discussion Starter #5
<div class='quotetop'>QUOTE (priesman64 @ Feb 20 2010, 11:37 PM) <{POST_SNAPBACK}></div>
have you tried this out yet?[/b]
Like i said in my first post, i jusst got them wound and the next step is to get them into the stator and then into the sled. Will have it all done by Monday evening because I have some commitments tomorrow.
 

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<div class='quotetop'>QUOTE (109jb @ Feb 20 2010, 10:40 PM) <{POST_SNAPBACK}></div>
<div class='quotetop'>QUOTE (mopar4u @ Feb 20 2010, 11:36 PM) <{POST_SNAPBACK}>
Nice, keep us posted on how it works out in the sled.

Did you varnish the coils after you wound them?[/b]
Not yet. Actually, I am planning on encasing them in JB-weld epoxy. The specs say that it is good to 600 deg F and doesn't conduct electricity. I will do that once I get them back in the stator and hooked up to the stator harness.
[/b][/quote]


Careful what you varnish them with, you want the heat to be able to get out of the windings.
 

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Discussion Starter #8
<div class='quotetop'>QUOTE (mopar4u @ Feb 20 2010, 11:42 PM) <{POST_SNAPBACK}></div>
Careful what you varnish them with, you want the heat to be able to get out of the windings.[/b]
Yep, agreed. However, because of the environment that the coils operate in it may be more important to keep moisture and contaminants out. I have been in contact with Kev and it appears that he encases his rewinds with epoxy too. Not JB weld, but epoxy nonetheless. Also, the original coils were pretty well encased in epoxy too.
 

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I'm looking forward to hearing the results. From what I understand, the further the wire is from the core, the less voltage it produces. I'd be interested in peak voltage comparisons.

Not sure why, but the failures I see on EFI's are on average different then carb sleds. If successful, I believe this is most beneficial on batteryless EFI sleds.

I've been considering aircraft wire rated for 240C as another option. Coating is thicker which makes coils fatter and changes the length of copper used.
 

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<div class='quotetop'>QUOTE (kev @ Feb 21 2010, 09:15 AM) <{POST_SNAPBACK}></div>
I'm looking forward to hearing the results. From what I understand, the further the wire is from the core, the less voltage it produces. I'd be interested in peak voltage comparisons.

Not sure why, but the failures I see on EFI's are on average different then carb sleds. If successful, I believe this is most beneficial on batteryless EFI sleds.

I've been considering aircraft wire rated for 240C as another option. Coating is thicker which makes coils fatter and changes the length of copper used.[/b]
when I worked at an electric motor manufacturing facility we called this "heavy build" vs the standard "single build". I think that is what your talking about. More expensive, thicker but more resistant to breakdown.

I would love to get into rewinding of these stators but unfortunately I'm not knowledgeable in the engineering aspect of electrical knowledge.
 

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Discussion Starter #12
Small update.

I got the bobbins back in the stator frame and coated with JB weld. After getting everything done I decided to ohm check everything on the stator. Pulled out my Craftsman DMM and everything checked good except the lighting coil. Son of a $#%#!. Should measure about 0.1 ohms and mmeasures 0.9. Beat my head against the wall, curse, almost throw the darn thing across the room. Decided to pull out the trusty old analog meter that my faather handed down to me. Now lighting coil checks 0.09 ohms. within tolerance. Turns out my Craftsman DMM has a "feature" where the decimal doesn't move for resistances lower than 0.1 ohms. Even though the display read 0.9, the actual was 0.09. Big sigh of relief and went to bed. That was 2 am this morning. I had family commitments today so won't be able to get to it until later tonight to get it in the sled. Just logged on from dad's house to check things out.
 

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You'd have to go to a real high end multimeter to ever measure a lighting coil within the tolerances listed in the manual. Most of the time the closest my digital meter will read is 0.2 ohms. Lighting coils are very reliable so nothing to worry about.
 

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Discussion Starter #16
<div class='quotetop'>QUOTE (kev @ Feb 21 2010, 05:00 PM) <{POST_SNAPBACK}></div>
You'd have to go to a real high end multimeter to ever measure a lighting coil within the tolerances listed in the manual. Most of the time the closest my digital meter will read is 0.2 ohms. Lighting coils are very reliable so nothing to worry about.[/b]
Yeah. The analog meter that my dad handed down to me is an old Simpson that can get down to that low resistence. It has just been my experience with my craftsman DMM that it is very good too. I guess not as good as that old Simpson.
 

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Another thought. If you go by length, as the circumference increases the total number of turns for that given length decreases. This could result in a less then ideal voltage.

On these models, it seems inadequate stator voltage could result in not being able to achieve full RPM. When you go to test, can you verify it reaches full RPM?
 

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Discussion Starter #18
Update. I found out that I have to go out of town for work tomorrow morning. Will probably be out of town for 3 or 4 days and couldn't bring myself to wait that long. So, when I got home from visiting my father I installed the stator into the sled. I just came in from the barn and here is what I have found so far.

The stator fit with no interference problems. I was a little concerned that the low speed coil being so fat now would have that coil rubbing somewhere, but that was not the case. The wiring on the back side cleared the stator mounting bracket just fine. The other side was pretty much even with the rest of the coils which I confirmed by laying the stator on a flat surface (table saw table. So clearance was not a problem. Everything with installation went fine.

The sled started on the 2nd pull just like always when it has been sitting for as long as it has. Idle was spot on at 1500 rpm and stable like it always was a few seconds after start up. It was in the barn and on dollies so I couldn't get it up to clutch engagement rpm. I did rev it from idle to about 3500 rpm and everything performed as normal to that point at least. I shut it down and restarted it several times and on subsequent starts to the initial start it fired off on the first pull each time.

I haven't run it to full rpm yet and it sucks that I have to go out of town because the snow is falling outside right now. We are supposed to get about 4 inches. I plan to call a buddy of mine and have him run it around a little.\ tomorrow since I can't. I'll post what he finds.
 

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Discussion Starter #19
<div class='quotetop'>QUOTE (kev @ Feb 21 2010, 09:02 PM) <{POST_SNAPBACK}></div>
Another thought. If you go by length, as the circumference increases the total number of turns for that given length decreases. This could result in a less then ideal voltage.

On these models, it seems inadequate stator voltage could result in not being able to achieve full RPM. When you go to test, can you verify it reaches full RPM?[/b]
Yeah, I thought about that too. I decided that I would initially wind them according to what the stock length should be since I didn't know how many turns the stock coils had. We'll see if it works that way. One thing I will say is that the low speed coil will just have to stay that way because I don't see how you could get any more wire on that bobbin. The high speed coil you could absolutely get more wire on to compensate for the increased diameter of the wire. I have a counter that I could have rigged up but I couldn't find it so I wound them by resistance anyway. For the high speed I put on as much as I felt I could and the resistance was very close to what I calculated.
 
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