# powdered iron toroids as coil cores?



## GrowleyMonster (Apr 7, 2014)

I am thinking about winding stator coils for a homebrew axial flux BLDC motor, using for cores T400-26 toroid with a 1.5" gap cut out of the toroid. The rotor magnets will pass through the gap. Is this a dumb idea or is it worth pursuing? The unmodified toroid has a 4" outside diameter and 2.25 inside diameter and it will be wound with 2 layers of 10ga wire, total of around 88 turns for 48v, all coils in each phase in parallel, Y connected. It looks like a way to get a lot of copper into the stator, keep resistive losses low, and get good efficiency out of a long coil form by essentially bending it into an interrupted circle with the core making a good magnetic circuit. I just thought it might be worth looking into. Thanks.


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## kennybobby (Aug 10, 2012)

Will this be an attractive-force or repulsive-force motor, i.e. between the rotor magnets and the toroid end poles? How many toroids, how many magnets and how many electrical phases? 

My guess is that such a device could probably be made to rotate but would likely make no torque or less.


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## GrowleyMonster (Apr 7, 2014)

kennybobby said:


> Will this be an attractive-force or repulsive-force motor, i.e. between the rotor magnets and the toroid end poles? How many toroids, how many magnets and how many electrical phases?
> 
> My guess is that such a device could probably be made to rotate but would likely make no torque or less.


Both, I guess. 3 phase. The magnets passing between the two poles of the coil. When between two coils, the previously passed coil is energized to repel, acting on both poles of the magnet, and the next coil attracts. When the magnet is adjacent to the next coil it is not energized. As it passes that coil, the coil is energized in the opposite polarity and pushes with both its poles on both poles of the magnet while pulling on the next magnet, and the next coil is attracting both poles of the first magnet. Just like a normal axial flux 3 phase BLDC motor except both poles of the magnets and both ends of the coil are used and the magnetic flux of the energized coil is confined into an interrupted ring. The magnets pass through the gap.

24, possibly 36 coils. 2 magnets for every 3 coils like most 3 phase BLDC motors. Commutation either by hall effect sensors, or optically, but probably hall effect. Controller will be a Kelly KBL series or home brew of similar operation. Motor function is propelling a small (7600 lb) sailboat at low speeds, direct driving a fixed 3 blade 12x12 prop and regenerating when under sail at or near hull speed. So I am looking for low motor rpm, not compact size.

In a normal BLDC axial flux motor, only one pole of each magnet is fully utilized, and only one end of each coil. I am just wondering if that is really the best way to do it.

Thanks for the reply!


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## major (Apr 4, 2008)

GrowleyMonster said:


> In a normal BLDC axial flux motor, only one pole of each magnet is fully utilized, and only one end of each coil. I am just wondering if that is really the best way to do it.


Hi Gro,

You clearly do not understand magnetic circuits. You cannot avoid using both poles of a magnet equally. Saying "only one pole of each magnet is fully utilized" is like saying only one terminal of a battery is fully utilized  

I suggest you study magnetic circuits and when you understand Ampere's Law, you will see why your toroid cores will be less effective than conventional methods.

Good luck with it,

major


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## kennybobby (Aug 10, 2012)

It sounds like an interesting approach--maybe build a single-phase prototype for proof of concept and torque testing. i have used a large PM axial flux motor as a generator (700 rpm = 700 vdc out of the 3-phase rectifier bridge) and the cogging torque (attraction of magnets to stator poles) was quite large.


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## GrowleyMonster (Apr 7, 2014)

major said:


> Hi Gro,
> 
> You clearly do not understand magnetic circuits. You cannot avoid using both poles of a magnet equally. Saying "only one pole of each magnet is fully utilized" is like saying only one terminal of a battery is fully utilized
> 
> ...


Thanks for reply, Major. Ok I see what u mean. But back to the coil, is there no advantage to completing the magnetic circuit with something having greater permeability than just air? Hope I don't sound hard headed and ignorant, I just want to hear a little more before discarding the idea altogether. But I don't want to waste time or money, especially money, on a concept that simply can't work, either. Anyway thanks for your response, which actually was very helpful.


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## GrowleyMonster (Apr 7, 2014)

kennybobby said:


> It sounds like an interesting approach--maybe build a single-phase prototype for proof of concept and torque testing. i have used a large PM axial flux motor as a generator (700 rpm = 700 vdc out of the 3-phase rectifier bridge) and the cogging torque (attraction of magnets to stator poles) was quite large.


I have built a 3 phase PM motor but never single phase so not quite sure even how it works, lol! But I was indeed considering a 9 coil or 12 coil motor using the same toroid and wire, before building the full size one. Wouldn't push my boat very well, probably, but could always use it as a wind generator, or of course re-use the magnets and cores in mkII. One problem is the toroids. To get them at a reasonable price I need to order 100 of them. From Amidon they are I think $11 each in small quantities, way more than the magnets. Either way, a small prototype is gonna cost a very large fraction of what the full size one would cost, anyway.

No, I'm not trying to save money with this, cause I know that is impossible, with '4201 motors going for under $400, but still I have to keep cost reasonable, and not go for it at all if it simply can't work.

I guess it is all about the difference between a cool idea and a good idea. The cool idea is the one that excites the imagination. The good idea is the one that can be made to work well.


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## major (Apr 4, 2008)

GrowleyMonster said:


> But back to the coil, is there no advantage to completing the magnetic circuit with something having greater permeability than just air?


You betcha  Pretty much all motors complete the magnetic circuit with iron. Only the coreless types use air for a magnetic path. Realizing they all need the air gap to provide any motion.

Your problem is so little copper passing through the magnetic circuit. See Ampere's Law.

Then throw in the low flux density saturation level of powered iron compared to sheet steel and you'll end up with very poor active material utilization, ie. poor torque density.

For a motor capable of power you need a generated voltage in the armature conductors and torque produced from the interaction of the current in the armature conductors and flux.

As the magnets rotate in and out of your cores, the flux will change therefore generating a voltage on the conductors passing thru the cores.

The force is the vector cross product of the armature current and the flux. This means the direction of that force is 90º to the current and 90º to the flux. The typical motor has this force in the tangential direction which then produces torque at the axis of rotation. Your cores and coils are positioned such that the force will be in the radial direction. So I am having a difficult time seeing how any meaningful torque will result.

I'll post here a thread where a fellow attempted to build a motor with cores and coils oriented like what you described. He faded away and I seriously doubt had his machine complete a single rotation under its own power. http://www.diyelectriccar.com/forums/showthread.php?t=42238&highlight=alaskastar


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## GrowleyMonster (Apr 7, 2014)

major said:


> You betcha  Pretty much all motors complete the magnetic circuit with iron. Only the coreless types use air for a magnetic path. Realizing they all need the air gap to provide any motion.
> 
> Your problem is so little copper passing through the magnetic circuit. See Ampere's Law.
> 
> ...


I don't see how that guys motor would run. Seems a little, errrr... eccentric? In a way, it could be said that i am proposing orienting coils to magnets in similar fashion. But my coils are on a C shaped form. Picture a donut. Now picture a segment cut out of the donut so that it is shaped like the letter C. Now picture the incomplete donut wound with coils of wire, beginning at one side of the gap and continuing to the other end. Also i would be using the conventional 2 magnets to 3 coils configuration.

The reference permeability of the type 26 core material is 75 and the toroid itself is fairly massive, .650" thick and .875" from outer to inner surface, for a cross section of .56875"sq. The wound coils will have no significant gap between one another, so quite a bit of copper there.

So how does laminated steel typically compare to type 26 powdered iron? Would this thing have a chance if made with C-shaped laminated steel cores?

Just to make sure you can picture my idea, here is another representation. Picture an ordinary axial flow motor with a rotor disk carrying magnets, and a stator disk carrying coils. Now picture the motor with longer, rather than flat coils. I know, the coil calculators all tell me that a flat hockey puck shaped coil produces a stronger field, but I'm not done yet. Now picture this long coil bent around in a circle, so that the free end is now directly facing the other side of the rotor disk. There, like the first side, a coil faces, end-on, a rotor carrying magnets.

And let's look at this... A motor having a permanent magnet rotor and two coil bearing stators, will work, right? 

I am just about ready to listen to you and drop the idea altogether if you still say "nope, no way". But i think the coil field is indeed oriented just like an ordinary motor, and the coils energized in proper phase sequence should push/pull the magnets in a tangential vector. Then again i might be missing something here.


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## kennybobby (Aug 10, 2012)

Are the cores covered with a ceramic coating? How will you make the clean cuts to create the 'air gap'?


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## GrowleyMonster (Apr 7, 2014)

kennybobby said:


> Are the cores covered with a ceramic coating? How will you make the clean cuts to create the 'air gap'?


Dremel with cutoff wheel, then sand to final dimension. Obviously a few practice cuts will be needed, but final gap will be something on the order of 1.5" so I can make a few preliminary cuts. I think I can make cuts that will be quite sufficient. The ends I will maybe coat with epoxy. The cut is not a major concern. Whether the thing will work is the real issue.


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## major (Apr 4, 2008)

A diagram would help. Or get a doughnut, piece of string and CD and take a photo 

edit for additions:

How about this? http://www.youtube.com/watch?feature=player_embedded&v=dsTMgb_jKUg

Or this?












http://www.bibliotecapleyades.net/ciencia/ciencia_flyingobjects57b.htm


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## GrowleyMonster (Apr 7, 2014)

major said:


> A diagram would help. Or get a doughnut, piece of string and CD and take a photo
> 
> edit for additions:
> 
> ...


Well, that drawing still doesn't show the coil wound on the entire core thingie. Also if I am looking at this right, there are half as many magnets as coils, so apparently not a 3 phase motor like I have ever seen, and not much copper there at all. I really don't see how it can work at all, if I am looking at it right.

My resources are a bit limited at present. I am on a ship anchored off Caldera, Costa Rica. We don't have any donuts but maybe there are some in Punta Arenas. Hopefully there will be a berth available for us in a couple of days. My Internet connection is shared with the whole ship, comes via satellite, and bandwidth is too small for you tube. I will try to work up a sketch but having just recently switched from windows to Linux I am still learning to work with some drawing and image editing tools. I will try to draw freehand and take a pic of the drawing with my android.

LOL ok u got me with the flying saucer! No that isn't what I want to do at all haha.


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## Tesseract (Sep 27, 2008)

GrowleyMonster said:


> So how does laminated steel typically compare to type 26 powdered iron? Would this thing have a chance if made with C-shaped laminated steel cores?...


The typical grade of silicon steel laminations used for transformers and motors has a permeability of ~8000 and a saturation flux density of 1.5-2.0T.

However, when you introduce an air gap to a wound core the reluctance of the air greatly reduces its effective permeability.

The below page does a good job explaining this and even has an effective permeability calculator:

Encyclopedia Magnetica


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## major (Apr 4, 2008)

GrowleyMonster said:


> LOL ok u got me with the flying saucer!


I had a great deal of trouble finding an image of the C core like you describe. But at least now I know how flying saucers work 

The vid isn't great quality but does show a C core disc rotor motor, 2 pole (1 coil) single phase. I'm amazed it works. Maybe it is a trick.

Regards.


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## kennybobby (Aug 10, 2012)

major said:


> I had a great deal of trouble finding an image of the C core like you describe. But at least now I know how flying saucers work
> 
> The vid isn't great quality but does show a C core disc rotor motor, 2 pole (1 coil) single phase. I'm amazed it works.


At least the spacecraft motor has the correct Flux Capacitors.

The secret to the C-core motor is painting a spiral pattern on the rotor--and that it is an overunity device that powers up the LED lights while spinning the motor, hence creating more power than it consumes...


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## GrowleyMonster (Apr 7, 2014)

kennybobby said:


> At least the spacecraft motor has the correct Flux Capacitors.
> 
> The secret to the C-core motor is painting a spiral pattern on the rotor--and that it is an overunity device that powers up the LED lights while spinning the motor, hence creating more power than it consumes...


Well, if there are LEDs, then you could have them charging high efficiency solar panels for a bigger net energy gain.😊


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## GrowleyMonster (Apr 7, 2014)

major said:


> I had a great deal of trouble finding an image of the C core like you describe. But at least now I know how flying saucers work
> 
> The vid isn't great quality but does show a C core disc rotor motor, 2 pole (1 coil) single phase. I'm amazed it works. Maybe it is a trick.
> 
> Regards.


I am guessing it would never do any real work. But I will check out the video when I have a proper Internet connection.


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## GrowleyMonster (Apr 7, 2014)

Tesseract said:


> The typical grade of silicon steel laminations used for transformers and motors has a permeability of ~8000 and a saturation flux density of 1.5-2.0T.
> 
> However, when you introduce an air gap to a wound core the reluctance of the air greatly reduces its effective permeability.
> 
> ...


Hey thanks for the numbers, and for the link. Is this type of steel hard to source, for a DIYer? And how does ordinary sheet metal compare?

As for the lamination orientation, do induced eddy currents generally run in same direction as coil current? And so, to implement this core shape with laminated steel, would it be a simple matter of stamping out a stack of C shaped pieces, varnishing or epoxying, then stacking? Or am I looking at strips of steel, bent, then stacked one inside the next? Or would either one work?

I will check out the site u gave me as soon as I am off watch. Thanks for the link!


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## GrowleyMonster (Apr 7, 2014)

Okay here's a crude sketch of a single coil. A complete motor will have 24 to 36 of them, squeezed right next to one another in a stator ring, and the rotor disk will rotate with the magnets passing through each coil gap in turn.

Hope the pic posted ok. As shown, core is wound with 2 complete layers. That would be 9ga wire and about 78 turns. 10ga would give me I think I calculated 88 turns. I just did some rough calcs since this is still a pretty vague idea at this point. The 10ga wire would actually be 1 full layer and about 3/4 of a second layer for 48v. I tossed the paper I figured that all up on since it certainly wouldn't be the final turn count, just an estimate. Each phase will have its coils connected in parallel but of course I could use a series/parallel configuration for higher voltages. I picked 48v for a variety of reasons not least of which initially this boat will have a 48v bank and electronics, and a Motenergy BLDC motor installed. I HAVE to repower with SOMETHING, very soon, as in right when I get home, and 48v stuff for boats is pretty common, and a good compromise. The C-coil motor, as I guess it is now called, will be an experiment that might or might not be a permanent upgrade to the boat. Mostly I just thought it would be a cool idea to try. 

I'm not yet fully convinced it will work. I'm not convinced that it won't work, either, yet. You guys know more than me, which is why I came here for advice. Ok lemme hit submitvreply, and see if the pic posts ok.


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## arklan (Dec 10, 2012)

reminds me a bit of one of these


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## major (Apr 4, 2008)

GrowleyMonster said:


> Okay here's a crude sketch of a single coil.


Yep. That is exactly how I imagined it from your first description. Your sketch is pretty good.

Here is the relationship of flux, current and force. Google: right hand rule force current magnetic field. It is the direction of current as it passes thru the magnetic circuit. So I see the resulting force being radial with your configuration.










major


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## GrowleyMonster (Apr 7, 2014)

Okay then, I guess I will stop pursuing this line of thought and let this thread die a peaceful death. Thanks for listening and thanks for the feedback.


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## kennybobby (Aug 10, 2012)

Just out of curiosity, how were you planning to hold the C-cores in position around the rotor, and what about bearings for the rotor shaft?


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## GrowleyMonster (Apr 7, 2014)

Bearings in the casing end bells. Stator ring in two halves, bolted together, fiberglass or some other composite.


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## kennybobby (Aug 10, 2012)

Many folks have built motors using a similar concept to that you proposed and have videos on the utubes to show them working. Those are mostly free-energy sort of schemes and the motors don't start without a push. 

But you have obviously spent some time thinking thru this and aren't trying to extract free energy from the universe...and there is nothing fundamentally to prevent your 3-phase motor from working, although the efficiency may not very good and the torque may be lower than other motor types, but for a sailboat it may be adequate. Lots of work to build a motor from scratch is all. 

Are you constrained very much by weight or volume? If not you might consider using a 3-phase AC induction motor with a variable frequency inverter as a low-cost solution. Or find an excess 3-phase BLDC servo motor from a surplus store.


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## GrowleyMonster (Apr 7, 2014)

kennybobby said:


> Many folks have built motors using a similar concept to that you proposed and have videos on the utubes to show them working. Those are mostly free-energy sort of schemes and the motors don't start without a push.
> 
> But you have obviously spent some time thinking thru this and aren't trying to extract free energy from the universe...and there is nothing fundamentally to prevent your 3-phase motor from working, although the efficiency may not very good and the torque may be lower than other motor types, but for a sailboat it may be adequate. Lots of work to build a motor from scratch is all.
> 
> Are you constrained very much by weight or volume? If not you might consider using a 3-phase AC induction motor with a variable frequency inverter as a low-cost solution. Or find an excess 3-phase BLDC servo motor from a surplus store.


Weight and bulk are non issues. But I already have an immediate low cost solution, which is a $375 Motenergy motor and Kelly controller. I do want a fuller understanding of motors especially PM motors, and I do want to build one to suit me, possibly next year. I may end up deciding that the off the shelf motor is better, and I am not gonna do it to save money or anything. Mostly I just want to do it.


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