Coil shape for axial flux generator

[joestue]

Ferrite can easily be cut with a diamond blade, but it will make a mess.

Cutting square blocks into wedges decreases the total volume of magnet, so you're paying more for less magnets.
If you can buy ferrite in say, foot long blocks, and then cut them with a 1/32 inch thick saw blade, i would try that. but its a lot of work to try and get higher density magnet spacing.

Also, the only reason that you want magnets covering say, 160 out of 180 electrical degrees is that you have thin magnets, and an iron core, and are trying to reduce the cogging torque to an optimal value. (180 degree magnet coverage is when you have pie shaped magents that touch each other)

The topology of these air gap machines is that you've got half inch thick mangets that are 1 inch wide. this is not a topology that would ever be used with an iron core for anything but some kind of experimental, intermittant duty machine, so i don't see any point in trying to get the magnet gap below half the width of the magnet. This statement will have to be experimentally figured out with a very high pole count machine. (given that only square magnets are available)

For example, a 96 pole, 1/2 inch wide, 1/8th inch thick by 1 inch long magnet would fit on a 19 inch diameter disk would make a great test structure for finding out if pushing the magnets closer together could result in a higher torque density.

[electrondady1]

go to a hock shop . the cheapest tile saw with a diamond blade can cut ferrite mags .
the water cools the mags down so they don't lose magnetism.
you can use mags from loud speakers and micro waves .
you want to use some kind of jig to create precise and consistent angles .
the cutting residue is not magnetic
it  behaves like iron filings.
i ended up saving it to do experiments with mag spacing and air gaps etc.
 you can cut up neo mags as well.

 

[gww]

I found microwave magnets to be stronger then speaker magnets and also to have north/south polarity on there faces.  It was hard to get enough of exactly the same size though.
gww

[derekisastro]

For radial with an iron core all machines use the convention that has been established over the last 100 years. A single phase winding will have one coil group per pole, each coil may be one of several in a pole group. If you treat it as a virtual pole design you halve the number of pole groups and wind them wider.

When you go to 3 phase you just add two more windings at 120 electrical degrees and to do this the coil ends have to overlap. The coil per pole winding is usually done as a 2 layer winding, as a mush winding in small machines or with specially formed evolute windings in big ones. The virtual pole type is wound with coils of straight and variously bent ends called a concentric winding.

For single phase you can use the serpentine winding, it only needs one big single coil to wind then you thread it in and out of the pole slots. It is also common to do a similar thing but wind the poles as coil loops ( skein winding).

You can do this for 3 phase in small machines but the ends now conflict and you end up with overlaps as in a mush winding, it becomes less attractive. with iron cored slotted machines winding resistance is not a major issue, the output is limited by reactance and a bit of resistance just drops the efficiency a bit.

Flux

Why do radial wound generators have to have overlapping coils? Or is it just simply a matter of that by overlapping coils you get so much more copper and so produce so much more power? Not matter how much I've been trying to actually find the answer (or some form of explanation) I still can't find nor do I 'get' why they have to overlap? Why can't the coil structure be laid/made similarly to axial generators with no overlapping coils? (but rotated 90 degrees to be 'standing up' on end, if that makes sense?).

[CraigM]

Hello derekisastro, welcome to the forum.

Overlapping coils on a radially wound alternator will allow you to fill all available space with copper winding. This in turn makes the coils thinner because the winding is spread out over the entire surface area. You can choose to fill the winding space with fewer coils but you will then have thicker coils and fewer of them. Both examples will use the same amount of wire but you'll likely get less performance from fewer coils because their thickness will not allow for a close air gap.

You could make a radial alternator similar to an axial flux but would need to have an inner rotor and an outer rotor with a circular stator between them... Don't believe this would be and easy task. Building simplicity of an axial flux is one of its main strong points.

I started a radial alternator project and then put it on hold when it became apparent that building the steel core for the stator was going to be extra challenging. Remember you need to complete the magnetic flux circuit on any alternator. Either through magnet to magnet flux or from one magnet to laminated electrical steel flux.

Here are a few photo's. I don't have CAD running on my current computer so I'm unable to draw up a new sketch.

This is the drum I made from steel pipe and 1/4" sheet steel.



This is a CAD drawing for the design. 14 pole, 7 coils per phase, 3 phases (shown as blue, red, green)



Notice the coil thickness is 1/4 inch. This allows the flux gap to be much less then with fewer thicker coils.

Hope this helps!
CM

[JW]

Just did a quick search, forgive me if discouraging...

I don't think there is an answer to your question.

 https://www.fieldlines.com/index.php?topic=146453.0

Yes welcome to the forum

JW

[CraigM]

derekisastro,

The radial build project below is an interesting read.

https://www.fieldlines.com/index.php/topic,143807.75.html

A radial PMA can be accomplished they just require a different approach. Precision equipment such as a lathe will be required.

Hugh Piggott used a automobile brake drum for the rotor and a laminated core from an electric motor for the stator.

Here are a couple stators built to use a brake drum rotor.





Hope this helps,
CM

[JW]

Wow that is an interesting read CM,

I think derekisastro has a disadvantage because he has not reached the 20 post count to be able post links. I think thats why he quoted.

 the data base  is a definite advantage for us all

[derekisastro]

Hello derekisastro, welcome to the forum.

Overlapping coils on a radially wound alternator will allow you to fill all available space with copper winding. This in turn makes the coils thinner because the winding is spread out over the entire surface area. You can choose to fill the winding space with fewer coils but you will then have thicker coils and fewer of them. Both examples will use the same amount of wire but you'll likely get less performance from fewer coils because their thickness will not allow for a close air gap.

You could make a radial alternator similar to an axial flux but would need to have an inner rotor and an outer rotor with a circular stator between them... Don't believe this would be and easy task. Building simplicity of an axial flux is one of its main strong points.

I started a radial alternator project and then put it on hold when it became apparent that building the steel core for the stator was going to be extra challenging. Remember you need to complete the magnetic flux circuit on any alternator. Either through magnet to magnet flux or from one magnet to laminated electrical steel flux.

...

Hope this helps!
CM

Hey CM,
Thanks for the explanation, and yes, it helps to a degree, though still, irrespective of how much content I have consumed from all sources (and it's a lot), some of the explanation still is lacking ... don't get me wrong, I think the reason "because it's easy" is a totally legitimate reason and is probably enough of an explanation for me but it seems to me to not be the 'whole' reason.

As an example of what I mean, I get that your explanation of the radial generator and using overlapping coils leads to performance increases (?) due to having a smaller air-gap but then shouldn't the same logic apply to axial flux generators? Yet, on this same message board, I've seen the exact opposite explanation. That overlapping coils on an axial flux generator lead to thicker coil structure and so an increased air gap and so reduced performance ... you'll have to excuse my either misunderstanding or my trust in logic because to me, at the moment, that seems illogical, that overlapping coils leads to both thicker coils and greater air gap as well as leading to thinner coiling and reduced air gap.

Again, to reiterate, I do understand that by NOT having over-lapping coils in an axial flux design makes the design constraints much easier and simpler to deal with ... and that may be the best reason but having a radial stator in my hand, trying to wind over-lapping coils, I can't help but feel the same argument applies, without overlapping coils it would be SO much easier to wind! Does that make sense?

To also further help my understanding as well as understanding what I am talking about, I saw a great little axial flux design/coiling method on windstuffnow.com that, to me, seems to be quite a neat little design for an axial flux with overlapping coils. Am I somehow missing something in that design, other than maybe a slightly(?) increased difficulty in the design of the generator, that would lead to decreased performance issues?

Because the message board won't let me post links, I am referring to the Windstuffnow.com 3phase_turbine_kit in their store section ... the downloadable pdf instructions shows the winding I am talking about.

Again, thanks for the reply!

[CraigM]

Hello Derekisastro,

Let's see if I can help a bit. There may be other forum members better suited to explain but I'll give you what I know.

but then shouldn't the same logic apply to axial flux generators?

I remember seeing an axial air core alternator that was done with overlapping coils. One issue with this design was what to do with the coil shape that runs in the direction of the rotors... the top and bottom of the coils. This is where the coils overlap and bunch up. The coils also use much more wire causing increased resistance. Much of alternator design is compromise. Smaller coils grouped tightly together is the preferred method for an axial design.

I agree if winding coils for a radial design if would be easier to not concern yourself with overlap and just put coils side by side. I'm not sure you would achieve the same result because you're only using magnets on one side of the coil. You may not be able to get enough copper in the stator to reach a reasonable output. Except for some very early designs by Hugh Piggott using a brake drum and one other done by Oztules I have not seen a successful radial design. Motor conversions are preferred over a home made radial.

I'm familiar with windstuffnow.com, great web site. Believe the example you give has a wound steel core.

All good questions. Good to hear someone asking “why?” I'm building my first alternator and didn't follow the traditional route... that's just me. I'd encourage you to seek out your design ideas for a radial machine. Would love to see your take on it.

Best regards,
CM