Copper Concentration

[wdyasq]

Thinking of windstuffed's three phase coild winding and seeing the space covered by magnets and copper in DanB style alternators, I decided to just see how much more copper one might fit by a different tenique.  First, one must see if it may be worthwhile. Those are 1 X 2 X 1/2" magnets modeled just to give reference.

The areas as calculated from DanB's posting of his stator, a couple of guesses as to what may be effective areas of a different style winding. RHINO, my CAD program came up with the figures. From what is seen, one could stuff in more wire or move the rotors closer together.  As magnet flux is on the Square of the distance, it may make more sense to use the same amount of copper, wind it in a more compact matter and use the increased flux density to get higher overall output.

Another variable to consider,

Ron

[DanB]

Intersting post...  

The pros are obvious.

the cons are difficult construction and the fact that for every inch of wire you have in the path of the magnets youll have more outside of it I think.  (the ratio of 'useful wire' to 'wire thats wasted and only adding resistance' will get worse if you stack coils I think.  I think we concluded a couple of years ago that done right there is some small improvement but I don't recall the discussions that well.  I tried once 'filling up the holes' like that and getting solid copper around the whole thing with a 2 phase machine and it wound up with a thick stator and lots of wire stacked around the inside and outside of the magnet path.  To do it... every winding has to be a lot longer and I think that hurts you.

[Flux]

I built several machines with overlapping coils because that was the way I always wound radials. The problem with an axial is the lack of space at the centre, there is room for the overlap on the outside.

The other snag is finding room for the end windings. Not so difficult with a single rotor as the ends can be bent back past the core, but with a dual rotor you only have the thickness of the magnets to squeeze them in. This means that the magnets can not be potted in the normal way and the potting , which I consider essential for weather protection, needs to be cast accurately as a torus around the magnets.

I did my experimental ones with ceramic magnets ( pre sensible price neo) and I thought I could squeeze more out with the overlapped coils. Dan is right that the large amount of extra wire needed for the end connections defeats the object and it takes a great deal of skil and time to even produce a winding as good as the single layer type.

There are many cases where perfection makes little improvement and if it comes at a high cost in terms of complication and effort it is best avoided.

It is interesting to consider why all commercial motors and alternators use this approach. If you look at a 2 pole motor it has more wire outside the slots than in it by a big factor.

The fact is that with conventional machines the determining factor is not resistance, it is impedance and when the inductive reactance is greater than the resistance, resistance is no longer the thing that dictated the output and so a winding that gives a 10% increase in resistance will have no real effect.

In the case of the things we build here where they are tightly coupled to a battery, it is the resistance that dictates the output and anything that gives a higher resistance is at a serious disadvantage.

To gain anything from filling the total space it has to be done without increase of air gap or without increase of resistance. It may work out with a large diameter disc with many small magnets where the space is more realistic at the centre. With radials without slots there is a 30% gain from using a fully wound stator.

Flux

[electrondady1]

this is the direction my experiments have been taking for the last six month and i've had some success. at this point i need a new resin /adhiesive to be applied during the coil winding process. it needs to remain pliable and perferably none sticky during the assembly process. once in finished position the coils themselves must become the structural member for the stator as there is very little room for resin.

[wdyasq]

Thanks Flux and DanB,

I figured it would be a monster fitting the coils "near perfectly". I also had figured one would need a jigs to properly wind, bend coil ends, and place properly.  There would also be a jig to place magnets and epoxy cast only 1/3 the way up the magnet with a layer of light fiberglass cloth over the faces of the magnets for protection. I am actually thinking I may build a form, cast the "protection" for the top and sides, pull  magnets from those forms and then cast the rotor plates.  It would greatly reduce the amount of the "expensive" epoxy.  Although the gain would be in less weight and maybe better cooling of the stator.

I am helping a man now build an axial of the style DanB builds.  I will probably incorporate this in his rotors. I also plan on casting the stator with "holes" in the center and actually making a mold so less resin will be used. It will also have more "glass" than is normally used to keep it more stable. These ideas are to reduce use of valuable resources and possibly improve on some aspects of a fine machine. I do not see any benefit if I didn't have the tools and materials to build such molds and the desire to explore them.  I do not recall many mills "Burning Up" without reason.

A second stator might be built just to play with the idea of a thinner overlapping coil design. It is probably more of a PITA than it is worth.  Research is priceless.

Ron

[Gary D]

There is a different way to do less turns per coil on a 12 magnet duel air core machine. 36 coils (12 per phase) = less turns and the same approxamate resistance (same airgap). Electric Ed has an example of that below (will post link). However, his explanation would seem to make it simple to just wind each phase on it's own plane and shift each phase over 30(?) electrical degrees? The HUGE drawback I can see is all the soldering potential hotspots if a bad connection is made. However it must be noted that the same blade diameter can only extract the same watts at a given windspeed no matter how full the stator is with wire. This is from the uninformed (me),so please take it with a grain of salt....  Gary D.

http://www.otherpower.com/images/scimages/40/coils7.gif

[Gary D]

Sorry, I believe the proper link is below(was 140 not 40) my mistake :-(  Gary D.

http://www.otherpower.com/images/scimages/140/coils7.gif

[Flux]

I like your idea for protecting the magnets, it's a lot more trouble but if it was not for weather protection I wouldn't cast the magnets in at all but in this wet climate they wouldn't last long without protection.

If you do go for an overlapping coil design, keep the stator thin, less than 3/8," that way the ends are easier to deal with. You will still need reasonably thick magnets to have room for the end windings.  Even at 3/8" you would be better to split the bent coils into pairs back to back, the straight ones can be full thickness.

If you wanted to build several machines it would make more sense as the moulds and formers can be re-used.

Flux

[Gary D]

One last time trying here, if this doesn't work google electric ed....It's under coils 7 in his files. You can blow up the pic. to read and see this. The c in coils was a cap.

http://www.otherpower.com/images/scimages/140/Coils7.gif

[BigBreaker]

One advantage of having the copper bulging out around the stator is that you can pull heat out more easily.  I definitely mused on this stator configuration for that reason and to get more power out of the same magnetics, but wondered if the power improvement could be that great...

It seems like shrinking the airgap should have very diminishing returns at some point.  If all the flux crosses through the coil it doesn't matter whether that flux crosses an inch or a half inch.  It seems like airgap is more related to spreading, which should only really hurt once the gap crosses a certain threshold.  I guess the countering magnetic field from the stator coil makes spreading a constant problem, but still not inverse square of the distance...

Am I remembering my physics right?