Stator slot shape and magnet query

[Hilltopgrange]

Hi Guys

             I am just starting to a new wind turbine project but with a slight change to the normal. This machine will be radial flux with an iron core stator and the magnet drum on the outside, very similar to the A.W.P. turbine but with neos. I have most of the components gathered together and ready to roll.









This shows the tyre removed, I used a mortiser with a 1" chisel to cut off the tyre.





The magnet drum is the front drive wheel from a forklift truck and will need a little bit of machining to fit the magnets.













The original bearings and hub will also be used.

The stator lams are from an 11kw motor and I intend to machine new slots on the outside.





I have had a practise run on another old stator and it seems to work but I have a couple of questions to ask before I start to make the jigs etc.

This is the stator I intend to use.

My plan is to drill 36 slots with a vertical drill with a jig to maintain accuracy.  

The lams are welded on the outside but after drilling they will be turned down on the lathe, the lams will then be split and de-burred, skewed, varnished and pressed.

The magnet drum will have 24 poles around its circumference each being made up of  two 2x1x.5 magnets in repulsion, 48 magnets in total.

So that's the plan so far, I have no idea of blade size or expected output yet, the only part I am sure of is that it is going to be very heavy and will need a purpose built tower. That will please the wife!

So here is where I need some advice please!

Q1. is the shape of the stator slot critical? Most that I have seen are oval

Q2. Is it possible to use a round hole for the slot about 12 - 14mm dia

Q3. If two magnets 2x1x.5 are placed end to end in repulsion N-N or S-S will they act as one pole 4x1x.5?

Many thanks in advance

Russell

[paradigmdesign]

Very interesting, I am also building a radial PMA using 24 2x1x.5 neo mags.  I am also going with a 36 slot lam.  I am using a 10" brake drum is my magnet housing.

Q1 As far as the air gap, I am shooting for somewhere around 1/8", though that is a lot larger then most commercial designs.  

Q2 I know that a circle slot would not be the optimum shape, but I do not know how to calculate the change without testing.  I would assume it would increase the iron losses, due to the fact you don't have enough copper and thus too much steel close to the mags.

Q3 Yes though they may be hard to get together, those neos are very powerful at that size.

[paradigmdesign]

[Flux]

You must like hard work. I hate drilling any form of laminated material even when clamped between thick end plates.

I am sure round holes will be good enough but you will either reduce your copper area badly or have thin teeth between the holes and push the flux density in the iron.

For 24 poles you really need 72 slots for a sensible winding. I suppose you could do something with 36.

I think I would aim for the biggest holes that would leave you reasonably safe teeth from the mechanical point of view without bending or tearing during the drilling, probably 4mm. I wouldn't worry too much about tooth saturation, with your round slots the air gap to the base core would be reasonably short.

Personally I would go one stage further and not use slots at all. Keep the air gap short and wind the coils in the gap. That would save a tremendous amount of tricky work and you would not have to think about cog. The iron loss would be far less so start up would be better ( in your wind that may be no real advantage).

The output would be lower, mainly due to the less effective cooling without the windings being buried in iron for better heat conduction. Winding without slots is an order of magnitude more difficult, but when you remove the work of machining slots I still think it will work out easier.

If you want the absolute maximum output then go with the holes but even then it will not be as good as proper slots.

Two magnets end to end will test your patience but it can be done.

Have a look on Hugh Piggott's site for details on the brake drum alternator and the pages about modifications. ( can't get on the site at the moment to get the reference).

Flux

[Hilltopgrange]

Thanks for the reply.

I think the drum setup should work well and no nasty resin to worry about, I hate that stuff it gets everywhere!

I am aiming for abot 1/16 clearance, but it depends on how accurate the rest of the machine work is.

Russell

[Hilltopgrange]

Hi Flux,

        The hard work is no problem as my time is free but at the same time I don't like to waste time flogging a dead horse.

I contemplated making a hydraulic punch for the slots but it would take forever to do a 4 inch stack of lams. At least drilling the complete stack will be quicker.

If you think 72 slots would be better then that's what I will do. I think I need to spend a bit of time drawing it out full size to see how big I can go before I do anything more.

The winding type is another problem what would you recommend as a "sensible winding" I have an old book about generators etc and it shows the many different types of winding, is there a particular type you think would best suit?

I did consider Hughes method with the coils in the gap but I thought the slotted core would be better choice and more of a challenge, although I have enough of the lams to try both methods with a test coil! Maybe I should do a few experiments?

I have tried the two mags as one pole and would totally agree it's not easy but I think I have figured a jig to make it a bit easier or at least maybe save a few blood blisters.

Thanks again for your time.

Russell

[Flux]

You can wind each phase with 24 coils so that there is a coil under each pole or you can leave half of them out with coincident poles where you have a coil under like poles.

The first method will have 72 coils and each slot will have a top side of one coil and a bottom of another.

You can do it with 36 coils and each coil side will occupy a full slot. You have half the coils but twice the number of turns per coil.

There is very little difference in the result, but with pre formed large coils the winding method is different. The first method uses diamond shaped coils with an involute on the end and all coils are the same. The second method will require at least 2 coil shapes.

With this machine you can do it as a mush winding and you can manage with the same shaped coils by either method as you have plenty of room to take the end windings.

I suspect your biggest problem will be that the wire size will be too thick to wind and you will need to wind several strands in hand and you may even need parallel circuits.

With the 72 coil two layer winding you have the option of short pitching but I wouldn't bother with such short coil ends, I doubt that you will gain anything and it adds confusion when connecting. I would fit the coil sides in slots 1 & 4.

Ideally the gap between magnets should be about 1/2" for 1" wide magnets but not desperately critical.

Flux

[vawtman]

Hi Hilltop

 I dont think its a good idea to drill through lamiations because they need to be insulated from each other.

 If you drill through them you would short them.Maybe causing a heat problem near the coils.

 My .02 worth and have fun with your project.

[Hilltopgrange]

Hi Vawtman,

         after drilling I will be spliting the stack to debur the lams, I will then revarnish, skew and clamp the stack in a 10 ton press. Or at least thats the plan!

Russell

[Hilltopgrange]

Hi Flux

       Sorry for the delay it took a while to digest all that info and to check a few measurements and ref books.

I think I will be forced to stick with 36 slots, 72 would be just to tight and would weaken the stack.

The second method of winding that you mention sounds a bit easier for a first attempt. I have plenty of wire for a set of test coils to work out the turns and I will then get the wire and liners to suit, to be honest I wish I was at that stage. I am not looking forward to all the drilling, not that it is difficult just BOREING excuse the pun

36 holes 14mm dia x 4.5" deep = 162" that's 13.5 feet. I think I will need some of that lube that comes in green or brown bottles!

As luck would have it the gap between the mags works out at 12mm so almost the 1/2" you recommend

It looks like I now have the plan just got to build it.

 I will also need a new tower for this baby to sit on, my thinking is to build another freestanding tower about 60ft.

So that's my winter taken care off, I may tell the wife to expect to see me about April!

Thanks again flux for your time and help

Have you ever considered writing a book? I for one would buy it as I am sure many others would also, just a thought

Regards Russell

[vawtman]

Oops,sorry i missed that in the original post.

 Good luck with your project.