The Next Nerobro's HowTo: Doing the Stator Dance

[maclariz]

3) I made a tensioning clamp out of two blocks of oak bolted together. A shallow groove carved in the block made sure the wire didn't chafe on the bolts. This let me put full tension on the wire without cutting a groove in my fingers.

Would you mind drawing a quick piccy of what your clamp looks like, or sticking a photo on. Sounds like a good idea for not destroying my fingers. I have a few offcuts of beech around, so that may be similarly hard to the oak you mentioned and useable for the clamp. (Off course, there's lots of bits of pine kicking around, but that's probably too soft).

[Matchless]

Using wood is the best idea, use one side of a wooden washing peg. The back square part can square up the windings and push them tightly together, it can also be used to take the slight bow out of the windings so that you do not lose any space there.

[maclariz]

What am I doing wrong?????

I've tried rewinding my own Stator but things aren't going too well.

The first one failed for understandable reasons when a couple of windings chafed on the rotor, leading to an intermittent ground. But I was very careful with the second rewind and did it very neatly with only 35 turns, as opposed to the original 50 and this clears the rotor without trouble. Resistance according to my multimeter is about 1.2 ohms from any one yellow wire to any other. Resistance to ground is > 2 M ohms. Resistance from a yellow wire to the union of the three wires at the opposite end of the stator windings is about 1.0 ohms. Resistance with just touching probes together is about 0.7 ohms. The multimeter looks to be exactly the same as that used by Nerobro with a different colour scheme but all the same switch positions and ranges.

I would therefore correct the real resistances to the following:

Yellow wire to yellow wire: 0.5 Ohm
Yellow wire to union at end of stator 0.3 Ohm
Yellow wire to solder joint at start of stator ~ 0.1 Ohm

Basically this all seems to make sense. The total resistance seems a little low but the magnet wire is a heavier gauge than that used in the original (I used the following).

The output in AC volts from one yellow terminal to another is about 1 V at 4000 rpm and changes a little with RPM. But this is never going to charge my battery. What could I be doing wrong?

Could the insulation of the magnet wire be failing and allowing each coil to short out? Could I have damaged the insulation in winding?

Could something else be wrong that I haven't thought of?

BTW: I have checked the rotor. This seems to show alternating north and south poles facing inwards all the way round the rotor. Also, when I put the LHS cover on with the stator attached, it is pulled in strongly by the magnetic attraction. So, I don't think there's anything wrong with the rotor.

Thanks

Ian

[BassCliff]

I've tried rewinding my own Stator but things aren't going too well.

Resistance to ground is > 2 M ohms.

Mr. maclariz,

Are you saying that the resistance to ground is less than 2 Megaohms? If I understand correctly, there should be no continuity at all between any stator winding and ground, no connection whatsoever, absolute infinite resistance.

Thank you for your indulgence,

BassCliff

P.S. I'm glad this thread got bumped. This is a great write-up. Thanks Mr. Nerobro!

[maclariz]

Mr. maclariz,

Are you saying that the resistance to ground is less than 2 Megaohms? If I understand correctly, there should be no continuity at all between any stator winding and ground, no connection whatsoever, absolute infinite resistance.

What I said was greater than two megohms, i.e. no detectable continuity (as it should be).

[BassCliff]

No math before coffee!

What I said was greater than two megohms, i.e. no detectable continuity (as it should be).

Oops, got my symbols turned around. Sorry about that.

Don't the continuity readings between your stator legs seem a little low?



Thank you for your indulgence,

BassCliff

[maclariz]

Oops, got my symbols turned around. Sorry about that.

Don't the continuity readings between your stator legs seem a little low?

Yes, was wondering 'bout that.

But the resistance of the whole coil of spare wire is about 1.8 ohms, once the 0.7 ohm offset on the meter is subtracted. So the wire resistance is intrinsically rather low.

[Suzuki_Don]

Great article Nerobro. I would be prepared to attempt a rewind myself and as I have a spare in the shed I can do it and measure it for ohms as per the Stator Papers and have a good spare ready to go on the 550 when the other one plays up.

[maclariz]

BTW: I have checked the rotor. This seems to show alternating north and south poles facing inwards all the way round the rotor. Also, when I put the LHS cover on with the stator attached, it is pulled in strongly by the magnetic attraction. So, I don't think there's anything wrong with the rotor.

Now three phase AC was never on the syllabus where I studied, and I've struggled to find any really good primers on motorcycle generator/alternator systems on the internet. The best I could find last night was a wind power site using a similar idea of a permanent magnet rotor and a wound stator. Now their example uses six wound poles and four magnet poles. And it seems to me that working things out on a bit of paper, that the rotor needs a different number of magnet poles to the number of wound poles on the stator. I think from my calculations that 18 magnet poles and 12 wound poles (4 per phase) would work, as would 12 magnet poles and 18 wound poles (6 per phase). But I reckon that if you have the same number of magnet poles as wound poles, then all the phases end up in phase, and you lose the potential difference between at least two of the exit wires, and depending which way you connect the exit wiring, between all three wires. Now the point, my stator has 12 poles, my rotor also has 12 magnet poles. This sounds like a disaster. Could mean that although my winding is okay, the stator and rotor just do not match. In this case, my small exit voltages mean I have the odd pole here or there where I miscounted the number of windings....

I heard that there were two OEM suppliers of stators and rotors to Suzuki, Nippon Denso and Kokusan, with different numbers of poles on the stator (12 and 18, respectively). Certainly, mine has 12, but some stators I see on ebay or from various aftermarket producters for the GS400 have 18 poles. I am wondering if combining my 12 pole rotor with an 18 pole stator would work better?

Anyone know anything about this from proper education, rather than just my scribblings on bits of paper?

[Nerobro]

The nubmer of poles really would just affect the frequency of the a/c. So don't worry about that. You also can't just swap from an 18 to a 12 pole stator wtih teh same rotor. If the rotor has the wrong pole spacing you could just cancel any current.

I was quite worried with my stator that my resistance was to low. Resistance is really tied to the length of the copper used in the stator. The more copper, the more power you'll get from it. 35 turns versus 50 turns is a rather large difference. You may not have enough turns on the stator to make any real power. Also ALL the poles should be wound the same direction. To get the a/c they alternate the poles of the magnets in the rotor.

I'm going to have to say that either there isn't enough turns of copper involved, or you're still shorting to the chassis. With the motor running, have you checked to see if you get voltage between a yellow wire and the chassis?

[SPARKSS]

I've tried rewinding my own Stator but things aren't going too well.

The first one failed for understandable reasons when a couple of windings chafed on the rotor, leading to an intermittent ground. But I was very careful with the second rewind and did it very neatly with only 35 turns, as opposed to the original 50 and this clears the rotor without trouble. Resistance according to my multimeter is about 1.2 ohms from any one yellow wire to any other. Resistance to ground is > 2 M ohms. Resistance from a yellow wire to the union of the three wires at the opposite end of the stator windings is about 1.0 ohms. Resistance with just touching probes together is about 0.7 ohms. The multimeter looks to be exactly the same as that used by Nerobro with a different colour scheme but all the same switch positions and ranges.

I would therefore correct the real resistances to the following:

Yellow wire to yellow wire: 0.5 Ohm
Yellow wire to union at end of stator 0.3 Ohm
Yellow wire to solder joint at start of stator ~ 0.1 Ohm

Basically this all seems to make sense. The total resistance seems a little low but the magnet wire is a heavier gauge than that used in the original (I used the following).

The output in AC volts from one yellow terminal to another is about 1 V at 4000 rpm and changes a little with RPM. But this is never going to charge my battery. What could I be doing wrong?

Could the insulation of the magnet wire be failing and allowing each coil to short out? Could I have damaged the insulation in winding?

Could something else be wrong that I haven't thought of?

BTW: I have checked the rotor. This seems to show alternating north and south poles facing inwards all the way round the rotor. Also, when I put the LHS cover on with the stator attached, it is pulled in strongly by the magnetic attraction. So, I don't think there's anything wrong with the rotor.

Thanks

Ian

Howdy Ian. Your resistance readings look ok. Don't get too hung up on whether a winding "measures" a couple of hundred mohm one way or the other. Your reading showing >2Mohm to ground is more important and indicates, in all likelyhood that you're not chaffed badly either (as the likelyhood of a path to core...ground is most great). Even with many turns shorted, a short to ground and perhaps only one phase roughly intact, you'd have more than 1v AC between 2 line-line connections so this is a puzzler. You have MORE THAN ENOUGH wire wound to satisfy the output (I never wind that much). My first thought was that you might have measured using a DC meter........this will show erroneously because the source is AC (of course).
If that's not the case........and you've wound 18 poles with the 3 phases symetrically interspaced, then consider whether you have EACH POLE WOUND IN THE SAME DIRECTION - this is important........if, for example you found that it seemed to fit better to wind one one way and when you moved to the next, the other, then you'll set up a situation where the individual cycles are equal and opposite - bad juju......poor/no output.

[maclariz]

Rotor/Stator incompatibility

Well, I spoke to someone from Electrex today. He said that running a 12 pole rotor with a 12 pole stator will not work. I was thinking this was probably the case from some back of envelope calculations. In this case, all the wires produce volts in phase, and you get no potential difference between the pairs of wires.

His summary was:
For a 12 pole rotor you need an 18 pole stator.
For a 12 pole stator you need an 8 pole rotor.

Basically for every three poles on the stator, you need two magnetic poles on the rotor. This puts all three phases at 120 degrees to one another.

So, I've ordered the 18 pole stator from Electrex and I hope that this combined with my 12 pole rotor will start the thing charging again. I'll report back once I've fitted and tested it.

How the bike ended up with an incompatible rotor:stator pair is another mystery that will be down to one of its previous owners. I suspect that the stator broke and was replaced with a used one off another bike, which wasn't actually compatible.

[Matchless]

Well, I spoke to someone from Electrex today. He said that running a 12 pole rotor with a 12 pole stator will not work. I was thinking this was probably the case from some back of envelope calculations. In this case, all the wires produce volts in phase, and you get no potential difference between the pairs of wires.

His summary was:
For a 12 pole rotor you need an 18 pole stator.
For a 12 pole stator you need an 8 pole rotor.

Basically for every three poles on the stator, you need two magnetic poles on the rotor. This puts all three phases at 120 degrees to one another.

So, I've ordered the 18 pole stator from Electrex and I hope that this combined with my 12 pole rotor will start the thing charging again. I'll report back once I've fitted and tested it.

How the bike ended up with an incompatible rotor:stator pair is another mystery that will be down to one of its previous owners. I suspect that the stator broke and was replaced with a used one off another bike, which wasn't actually compatible.

How did you determine the amount of magnetic poles in the rotor? I have a rotor with 3 physical magnets fitted and the stator has 18 poles. The 12 pole stator will have a rotor with 2 physical magnates fitted.

[maclariz]

How did you determine the amount of magnetic poles in the rotor? I have a rotor with 3 magnets fitted and I think the stator was 12 poles, but not sure, as it has already been refitted. The theory sounds good, but I was wondering how to identify this easily if running around junk yards in future.

Yeah mine has 3 magnets too, but testing with a small fridge magnet, you will get strong attraction from one pole, strong repulsion from the next and so on. Each of my magnets had two areas of strong attraction and two of strong repulsion along it's circumference, i.e. 4 poles altogether.

As far as I can see, if you have 3 magnets, no maths using whole numbers can make this into 8 poles, but it is easy to make this into 12 poles. To have an 8 pole rotor, you would need two or four magnets mounted, so you can probably do it by visual inspection. But a small fridge magnet in the pocket is an easy way to be sure.

[mixongw]

Neropro: 18 awg. is thinner than 16 awg.