Author Topic: Dual Rotor Toroid Core PMA build  (Read 21768 times)

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CraigM

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Dual Rotor Toroid Core PMA build
« on: April 22, 2012, 04:30:08 PM »
Hello All,

I have a project I started and could use a little help and guidance.

First thing I'd like to mention is this build is more of a learning tool for myself on PMA theory and less of an exercise in getting this up in the air and making power. Flying it will come in time but I'm relocating to Florida soon and don't see the maiden flight happening for another year.

Specifications:
Dual rotor 11.250” OD
Toroid core 11” OD x 7” ID x .600 thick
Three phase, 24 coils, 8 per phase
Magnet poles, 8 per rotor, N to N & S to S facing each other.

A while back I came across some rather large sections of silicon steel at the local scrap yard. I started a radial PMA with the intent of using the silicon steel to make my own un-slotted core but it was slow going and a rather daunting task. So with a pile of extra material and a guillotine shear at my disposal at work I started cutting .600” wide strips to be wound as a toroidal core.

Much of the information gathered was gleaned from this posting. http://www.fieldlines.com/index.php/topic,145994.0.html

The winding of the core was rather uneventful as I was lucky to have 36” lengths of strip to work with. The material (.015”) also had the factory insulation so no extra insulation was added. I began the winding by using thinned epoxy between layers but this was really messy and hard to control so after only a few winds I switched to cyanoacrylate adhesive. I found I could wrap multiple layers and then apply thin CA glue to the edges and it would wick into the core and with a small puff of chemical vapor set almost instantly.



The next step was adding the coil spacers which were cut from .125” thick G-10 (also called Epoxyglass or Garolite). It's what I had on hand and an educated guess (at best) of how thick the coils will be. If needed I can always add to the spacer thickness by adding a thin layer of mmm… let's say balsa wood. The spacers were glued to the core using JB Weld and were held in place by magnets while the epoxy set up. It was slow going and a giant pain in the A$$ gluing 48 spacers to the core but it came out really strong. My first attempt was with 5 minute epoxy and wanting to know how strong it was I purposely tried to make if fail and it did. With the JB Weld I can hold on to the spacers and shake it back and forth with no failure in the adhesive. The photo shows a plywood ring (cut in two) that supports the assembly. Not sure how comfortable I am with the strength of the plywood so I may change this out with some Phenolic sheet. Each spacer will then be drilled and mechanically fastened to the support ring. The support ring of the stator will also have mounting holes to allow adjustment between the rotor plates.







So the bones of this PMA are nearly complete with a little cleanup work to do on the stator. What I need to decide (figure out) at this point is what gauge wire to use and what magnets to use. I'm leaning towards using Ferrite magnets (especially for the salt air of the Florida coast) but I'm unsure of overall size. In the posting mentioned earlier “Rewinding a Proven Stator” Flux mentioned keeping the flux density in the core below 1.5T and ideally lower if you want low core loss in low wind. How do you determine flux density in the core? If I take the tesla strength of ferrite at .38T and using for example a 1” x 2” x 2” magnet (feeding from both rotors) and condense that to the cross section of the core .6” x 2” I get 4 sq. in. magnet area divided by 1.2' core cross section = 3.333 x .38T = 1.266T in the core. Is this correct? Or can I push the magnet square inch size up until I hit the max 1.5T core density? I have my eye on 1” x 2” x 6” ferrite blocks that I'd like to cut into two wedge shaped blocks.

5446-4
Black outline represents 1" x 2" x 2" Ferrite magnet.

5447-5
Black outline represents 1" thick Ferrite magnet with 4.9 sq. inch of area.

The number of winds per coil will require a single test coil to be made first. The width between the coil spacers is .85” +/- .015” (best I could do eye-balling spacer placement). Depending on wire gauge (13 or 14) I should be able to get 12 to 13 winds in one layer. Ideally I'd like to get full layers (1, 2, maybe 3?) for each coil and not end up with something odd like one and a half layers to reach the desired cut in voltage. Have any ideas how to accomplish this?

I have to admit the electrical side of things is my weak point and what I need most to study and learn about. Mechanically I think I'll do okay but any and all input is welcome and appreciated.

Quite a bit to start a new post with, I'm sure I missed something.
Thanks, Craig
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #1 on: April 22, 2012, 06:48:23 PM »
Personally I would go overboard with the math, but that's me and my weakness.  As for giving advice, I think you've worked through it well enough to go ahead and do it.  The rough-size estimation of the magnets looks good enough to show that there will be an output of useful proportions.  Let the geeks make it better later.

One calc that I'd like to see first, since you haven't worked out how many turns to use, is a rough idea of the EMF per turn of wire.  With that you can get a voltage per # of turns, and that will start us working out wire gauge and turns for a given battery voltage.  I feel like opening a couple of the calculator webpages and see what drops out.  You've given a bit of geometry to start...

Have you worked out just HOW you will wind the thing's coils, yet?
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #2 on: April 22, 2012, 08:00:00 PM »
Back of envelope calcs say that 14 gauge may work out okay, but you will need two layers in the coil, with 13 turns in each layer across between the spacers.  I'm not sure how easy it will be to work with 14 gauge.  You can always wind "two-in-hand" with 17 or 18 gauge and get nearly the same result.
I'm coming to 250 RPM cut-in, for 12V battery charging, 3-phases in Star.
Phase resistance about 0.3 ohms maybe.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #3 on: April 22, 2012, 09:43:36 PM »
Thanks for the reply SparWeb.

In a previous post Hugh P. mentioned having wound a Proven stator and did so by transferring wire to a bobbin and then passing the wire through the center of the torrid core and winding the coils by hand. Having never worked with 14 gauge wire I'm not sure what difficulties I may run into. The coils are wound prior to attachment of the outer supporting ring.

I have no idea how you arrived at the approximate EMF per turn of wire using only the geometry given. Where can learn more about how to do this?

Thanks again,
CM
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #4 on: April 23, 2012, 01:33:17 AM »
My math was done hastily, there may be errors.
A good reference for physics/science math is Hyperphysics:    http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

I drew your stator to scale (not as hard as it sounds for a former CAD jock like me) and got 7/8" space between your wedges.  Wire wound between the wedges will lay relatively flat on the first layer and the second will settle on the grooves made by the first.  So a fair guess of the number of turns per layer is just the space across divided by the width of a wire.  0.85 / 0.064 = 13 turns, or thereabouts for 14 gauge, per layer.

Each turn is a loop, each loop encloses the laminations.  Taking your estimage of field intensity at face value (I can do no better right now) at 1.5 T and let's also say that it's evenly distributed through all the laminations (again I can't argue against it right now).
So that means that through every loop of wire 1.5T of mag field passes, and when the next magnet has come and gone the field will be -1.5T, meaning it points the other way, now.  The total field reversal is 3 Teslas.

Back to geometry, your laminate cross-section is 2 inches by 0.6 inches, or 1.2 square inches.  Now we must turn to the metric system because flux calculations in imperial is insane.  The area is 774 square millimeters.  Also worth calculating is the length of each turn:  perimeter of the rectangle is 139mm.  For right now all we need is the area enclosed in each loop, and get back to wire perimeter later.

The definition of FLUX is the total field that passes through a loop at right-angles.  Your loops fit this description, so through each turn, you can say that 1.5Teslas pass, and there are 26 turns if you put on 2 layers of 14 gauge.

1.5T * 774 mm*mm * 26 = 30186 microWebers.
This should be done in "meters" not "millimeters" so there are 1 million square mm in a square m:

30186 / 1,000,000 = 0.03 Webers.

A Weber is the standard unit of FLUX.   It's at this point that you can't mix up "field" and "flux".  Kinda like mixing up "Watts" and "Watt-hours"; they mean different things.  The flux is a unit of the field within a certain area, pointed in a certain direction.  Once the flux goes from N to S it will reverse the direction.  This is the effect that causes electrical potential to be created by electrical machines of all types.  The voltage you measure is scientifically called "electromotive force" or EMF which is produced every time the total Flux changes.  If the flux is constant there is no EMF.  Change the flux rapidly or change a large flux more slowly, either way it will produce an EMF which makes electrons move.

240 RPM is a nice round number that suits the speed of WT rotor blades at the size of machine you are building.   240 revolutions per minute = 4 revolutions per second.  Your rotor and stator have 8 "poles".  The flux will reverse completely 4 times per revolution.  Together your stator will experience 4*4= 16 flux reversals per second.

We're getting close to the end.  The formula for the EMF is to multiply the total change in flux by the rate at which it changes.

EMF = 2 * Flux * frequency = 2 * (0.03 Weber) * (16 per second) = 0.96 Volts

Each phase has 8 coils in it they will all be in series so their voltage will add:     0.96 * 8 = 7.68 Volts

If you connect the phases of your stator in Star, then the voltages on the line will increase by the square-root of 3.

7.68 Volts * 1.73 = 13.3 volts.

That is roughly good enough as a cut-in voltage for battery charging a 12 volts system.
The variables under your control are the wire gauge and size of magnets.  Increasing the magnets will add more flux (but at diminishing return) and reducing the wire size will increase the number of turns.  Doing either or both of these things will increase the voltage, and it's quite feasible to re-do this to size it up for a 24 volt battery system.

On the other hand, we haven't worked out the amount of current that will flow.  I'd better hit the "Post" button because I've typed enough already!
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #5 on: April 23, 2012, 01:50:24 AM »
Looking back I notice that I pointed out early on that the magnetic field reversal of 1.5T to -1.5T would give you "3 Teslas" but I shouldn't have put it that way.  Sorry for the confusion.  Below I went on and used 1.5T for the calculations, which is correct, so in the future just carry on that way.  when I calculate the EMF I multiplied the Flux by 2.  That's where the Flux goes from 0.03Wb to -0.03Wb so the total change is 0.06Wb.  I did it by multiplying by 2 in that formula, and after you get comfortable with the formula you'll see why it goes there.  But I started off on the wrong foot and hopefully I've cleared it up - not caused more confusion!   :-\

Going on with the math, then:
The perimeter around one turn is 139mm, making 26 turns give you 3.6 meters per coil.  Probably more like 4 meters because coils are never perfectly tight.  There are also 8 coils per phase so upwards of 32 meters per phase of wire (and 100 meters in the whole machine).  On each phase, then those 32 meters of wire will have some resistance.  Your 14 gauge has 8.8 ohms per 1000 meters, or 0.88 ohms per 100 meters, thus 0.28 ohms on each phase.  That's pretty good.  From before, I assumed you will wire it up in Star, so the line-to-line resistance will be 2x the phase resistance, equal to 0.56 ohms.

Now it gets less exact...

Turn the rotor faster than cut-in, say 2x cut-in speed.  At 480 RPM the EMF will be twice what it was at cut-in:  26.6 Volts.  Deduct from that the voltage of the battery, say 14 Volts, and there's 12.6 volts to push electrons through the whole circuit.  Pay the rectifier tax of 1.5 volts or so and:

Ohm's law:  11.1V / 0.56 ohm = 19 Amps.  Hey wow that's okay.  It won't light the world on fire but isn't a waste of time.

There you go, but it's all theory until you can go put it into practice.  Have fun!
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
System spec: 135w BP multicrystalline panels, Xantrex C40, DIY 10ft (3m) diameter wind turbine, Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #6 on: April 23, 2012, 12:01:08 PM »
SparWeb,

Thanks so very very much for the time and effort you put into this, I can't thank you enough! I don't want or do I expect to be spoon fed information but your reply and the link you provided will go a long way in helping me help myself.

I want a deeper understanding of why a PMA does what it does and not just build from a recipe book. Understanding the math and physics involved will help me move to the next level.

Again, so very appreciative of your time, now it's time to study and learn from your reply.

CM
« Last Edit: April 23, 2012, 12:25:05 PM by CraigM »
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #7 on: April 23, 2012, 12:39:46 PM »
That's what I'm in this for, too!   :)
I don't feel like the explanation above is spoon-feeding, because it brings together a lot of different stuff into one place for a specific purpose.
Not a lot of folks studied electromechanics in college, though.  It helps a lot in a hobby like this.

The most convenient table for wire gauge info is www.powerstream.com.  Their table is just a copy of a copy, (like everything else on the internet) but at least it contains all the facts you need to know in the same table, not just wire gauge in one table, resistivity in another, etc. etc.

One of the big guesses in all this is the field intensity that actually does pass through the laminations.  It could be 1T it could be 2T, and who will know for sure until you built it and test?  May I suggest that before you wind all 24 coils, do just 1 coil, and then spin the rotors, measuring what happens.  Small steps may prevent big mistakes, but by all means I hope this works!
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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jlt

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Re: Dual Rotor Toroid Core PMA build
« Reply #8 on: April 23, 2012, 05:36:55 PM »
    Wow that.s looking good. It cleared up how to attach the stator for me.

          What size blades are you going to try.

       The wood should work. If complete enclosed in the stator.

CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #9 on: April 24, 2012, 11:20:04 AM »
What size blades are you going to try.

Well, using the WAG principle, and the fact this is my very first build, and I should be stamping "experimental" all over this thing... hip shot target is 8 - 9 foot diameter blades.

The plywood stator support ring may be okay for testing but I have access to some .500 thick canvas phenolic sheet here at work and will use this for the final build. I feel it will hold up much better outside in the elements.

CM
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tecker

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Re: Dual Rotor Toroid Core PMA build
« Reply #10 on: April 25, 2012, 02:40:56 AM »
Looks like there's not enough winding room on the inside of the stator core .

jlt

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Re: Dual Rotor Toroid Core PMA build
« Reply #11 on: April 29, 2012, 11:00:16 AM »
My thoughts were to wind a stator core much like you would wined a copper coil.But with using mechanics wire.Then encase it in fiberglass.I would paint the mechanics wire with some acrylic
paint put on with a roller To keep it from shorting out .

             Not as neat as your  Stator but should work.
Eagerly awaiting your progress . thanks for sharing.

                                                                        JLT   

CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #12 on: April 29, 2012, 01:21:37 PM »
Finding small quantities of silicon steel sheet or strip is a big hurdle for many and it just doesn't seem to be available in the retail market. The next best option is using a very low carbon steel such as 1006 grade which has a .06% carbon content. The lower the carbon content the better and the lower your core losses will be. Annealing the material will also help reduce the carbon content while at the same time adding a resistive oxidation to the outside of the material. Also a very thin material (or wire cross section) will out perform a thicker material. Most silicon steel has a carbon content of .005% or lower.

If you live near a larger metropolitan area you may find scrap metal dealers with silicon steel scrap that's suitable. I live near Phoenix, AZ and there are several scrap metal dealers that have large quantities of silicon steel. Everything from small E cores to untouched sheets nearly 8" x 36". I work at a machine shop and we buy large amounts of sheet metal. I called 6 of our steel vendors asking for silicon steel and none of them knew what I was talking about. I then made a few phone calls to scrap metal dealers and as soon as I mentioned silicon steel they knew exactly what I was asking for. You may want to google "silicon steel scrap" and see what you can find. I've done this also and found material I could purchase at 100 lb. minimums. The scrap yards I've visited sell silicon steel at around $.70 per pound.

Of course if you do find silicon steel the next step is cutting it into strips. We have a guillotine shear here at work so that made it simple for me. However most sheet metal shops have a shear so you may have a friend of a friend of a friend that can help you out.

Another option if you're lucky to come across it is finding the "I" portion of E cores that have the width you need. I found these at a scrap metal yard, still wrapped in paper and fully annealed. (This material is well taken care of at the scrap yard with pallets of it stored in a shipping container) I did a few tests with it by overlapping each piece with the next and tacking them together with a drop of CA glue at the punch hole. I was able to then make lengths suitable for winding.





If anyone in the Phoenix area needs help locating silicon steel drop me an email and I'll let you know where it can be found.

Proof will be in the pudding as to how this PMA works out. I ordered 1" x 2" x 3" C8 ferrite magnets this weekend.

Time will tell,
CM
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #13 on: August 08, 2012, 12:49:36 AM »
Hi Craig,
Have you been able to progress on this project?
(Hoping a little encouragement will help) :)
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #14 on: August 08, 2012, 04:53:27 PM »
SparWeb,

I recently moved from Northern Arizona to the panhandle region of Florida and had to put the project on hold for awhile. Took me a month to box everything up and now that I've been here a few weeks I'm staring at a garage full of boxes and wondering where to begin. Honey-do list is a mile long too... sigh.

Have noticed that you can almost watch things rust here. Much different from the dry heat of AZ to the dripping wet sauna that's called Florida.

Should be back at it in a few weeks.

Thanks for asking,
CM

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DanG

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Re: Dual Rotor Toroid Core PMA build
« Reply #15 on: August 08, 2012, 05:16:57 PM »
The dry heat of AZ primed everything that could be primed into being ready to corrode. Once the introductions are over the oxidation should slow down enough to not keep you awake at night with the sputtering noises and dull red glows...

It'd be interesting to see if a substitution to a solid plate vs. the wound laminate would change outputs?

SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #16 on: August 09, 2012, 12:06:19 AM »
Craig,
No pressure.  Didn't know you were moving.  I wish you the best with all the new possibilities in your new home!

It's vaguely possible that a thin layer of corrosion will be helpful - only insofar as it isolates each lamination, but since the subject of Nomex interlamination sheets came up, it won't matter at all.  Or you could do without the Nomex at all....   ha, that's the evil Sparweb talking there.  You don't want any rust and especially not moisture in the laminations or it will eat itself away from the inside.


It'd be interesting to see if a substitution to a solid plate vs. the wound laminate would change outputs?

Probably a big detriment.  The eddy currents increase their drag in proportion to their size, read: diameter.  When induced through the thickness of a sheet then the diameter of each eddy can't be larger than the thickness of that sheet.  Eg:  1mm sheet -> 1mm eddy diameter.........but...........   12mm plate -> 12mm eddies.  Square the number for the area, and the result is a 144 X greater iron drag force.
(I think you're supposed to square the number to compare eddy-current forces; correct me if I'm wrong).
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #17 on: July 10, 2019, 10:15:31 PM »
Holy crap! Seven years since I started this post!

I always wanted to finish this PMA but life gets in the way. Mostly from a house renovation that took better part of five years. Bought a house built in 1960 and striped it down to the frame, only thing left was brick exterior, oak floors and frame. All new electrical, plumbing and insulation when in. It's small at 1500 sq feet but very efficient. Heating and cooling done by two small mini-split air conditioning / heat pump. A one ton on one end of the house and 3/4 ton on the other. Total electric, utility bill averages $100 a month.

So back to this PMA. I live in a poor wind area so it doesn't make sense to try and make this thing fly properly. I live on eight acres and have a five acre open pasture but it's surrounded by tall trees. Best I can think to do is "cringes" make this a yard art project, maybe something like a Lenz 2 savonius.

The PMA is patterned after the 2.5 Proven design. Not much info on the internet for this type of PMA but do know the Proven 2.5 uses two eight pole rotors and a 24 coil, three phase stator with a toroid core made from wound electrical steel.

Hugh Piggot talks about his time working with Proven on his YouTube channel. See link below at 8:30 into video.
https://www.youtube.com/watch?v=S5phDyk4590

So I'm at a point where it's time to wind a test coil and wanted some input as to how to measure current and test the PMA.

Here are some update photos:

11959-0
11960-1
11961-2
11962-3
This is the test platform built to hold the spindle. Sandwiched the spindle between two 2x4's put under pressure. Built additional 2x4 frame and covered it top and bottom with 3/4" plywood. Ends are open so I could reach inside to fix threaded rod for mounting the stator.

I'm only allowed 5 attachments per post to will end this and start a new post.

To be continued ~
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #18 on: July 10, 2019, 10:28:15 PM »
Continued ~

11964-0

11965-1

11966-2

The rotors are 11.5" diameter, .25" steel. Magnets are ferrite, 3" x 2" x 1" thick. Magnets were purchased as 2" x 6" and I cut them in half with a diamond blade on a tile saw. It's slow going but works well. If I had to do it again it's possible to cut a wedge shape from a 4" x 6" block and cram in more magnet material. Magnets are N - S - N - S on the rotor but will be oriented N to N and S to S when facing each other. With 12 square inches of magnet material per pole and a cross section of .625" x 2" (1.25 sq. in.) on the steel core, I believe this is called a flux concentrator. Hugh talks about this in the video posted earlier.

The last photo in the series above shows some 1.25" fiberglass material I will wrap and glue around the perimeter of the rotors. I will tack it in place with Cyanoacrylate (CA) glue and then use thinned epoxy to wet it out and attache to magnets and rotor edge. You can use rubbing alcohol to thin epoxy. Believe this will add a bit of strength to keep the magnets from flying off at high speed... they are quite heavy.

To be continued ~
« Last Edit: July 11, 2019, 07:43:34 AM by CraigM »
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #19 on: July 10, 2019, 10:53:13 PM »
~ Continued

11967-0

11968-1

11969-2

11970-3

11971-4

Next are photos of the stator and some of the issues that came up. When you're building something you've never done before you tend to take aim and give it your best shot. Sometimes you hit the bulls eye... most times you don't.

As shown much earlier in this post I started with a wound steel core. I had access to the material and after seeing how the Proven design was made it was a "why not" decision. Next came the spokes. I had access to G10 epoxy/glass laminate and was comfortable working with this material so I chose to cut these to size and glue them to the laminated core using JB weld. Electrical paper, can't remember the name of it, was used to insulate the steel core

You'll see in the photos I cut the spokes a bit short and had to add a filler piece (aircraft plywood). I also added a thin 1/16 filler piece on the inside of the spoke... will comment more about this later.

The last two photos show the addition of of a half round flexible molding piece I added. I tried a test coil wound over the square edges of the core and found the wire did not want to lay flat on the core. By adding the rounded relief the wire isn't require to make such a tight bend and is much easier to wind. This took up space however and is the reason why the spokes were now too short.

I used CA glue to fix the filler piece, plywood bits and the molding. As long as the parts are sanded to give them some "tooth" and they are close fitting with no gaps this is a quick way to glue up a bunch of small pieces.

To be continued ~
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #20 on: July 10, 2019, 11:24:32 PM »
~ Continued

11972-0

11973-1

11974-2

11975-3

11976-4

One thing I noticed when handling the stator over and over is that every now and then one of the spokes just didn't feel right. Kind of like a loose tooth. You couldn't see it wiggle but it didn't feel as solid as the others. I tried pulling one of the spokes off that didn't feel right and with some effort I was able to rip it off the stator. After this experiment I decided to drill and pin the spokes through the steel core. I used 3/16 G10 rod and CA glue to pin the spokes. After doing this I felt a noticeable improvement in the overall stiffness of the stator.

The ring that supports this assembly is made from .50" thick canvas phenolic, again, it's what I had on hand. The steel core is .625" thick so this is the reason for adding .0625" filler pieces behind each spoke. This worked out because it helped support the extra bits for the too short spokes. If I had to do this over the support ring would be the same thickness as the core.

You'll notice in the first photo every forth spoke (with the blue tape) does not have a hole drilled. These six spokes with be drilled to accept 3/8" threaded rod that will support the stator.

To be continued ~
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #21 on: July 10, 2019, 11:45:19 PM »
~ Continued

11977-0

11978-1

11979-2

11980-3

11981-4

Drilled the remaining holes today and did a test fit up of the rotors and stator. Somehow misplaced one of my 1/2" threaded rods for the rotors and that's why only three are shown.

Next step is to disassemble, remove the mounting ring and wind a test coil.

Now for the Q & A section... mostly me asking how to measure current and what am I looking for from the test coil.

Thanks,
CM
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #22 on: July 11, 2019, 12:29:07 AM »
Hello again,

So my questions to the forum members;

When winding a test coil I need to have a target as to what I'm trying to achieve. If this PMA is going to be used as yard art I thought of making a wood structure similar to an old water pumper windmill except to add a savonius type turbine and have it charge an on board 12 volt battery. Maybe use it for lighting at night.



I'm doing this just for fun and to learn along the way. I mentioned earlier that I don't have a good wind sight so I could go with a hawt which would be okay by me but will it preform without a good laminar air flow? Or does a savonius really work better in swirling winds or is that just a bit of public relations BS?

Here's my property, the large area near the top is maybe 4 acres but has a large pecan tree right in the middle. Remaining perimeter are tall trees.

[ Specified attachment is not available ]

I have a small spool of 15, 16, 17 and 22AWG magnet wire to get started.

Thanks much!
CM
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SparWeb

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Re: Dual Rotor Toroid Core PMA build
« Reply #23 on: July 11, 2019, 01:07:57 AM »
Holy smokes!  Back in a flash, Craig!  In just a wink of an eye...   ;)

If it's not too late -
Before you put a ton of glue on those magnets, consider what you want it to do:  bond in place, structurally, and protect the surface from corrosion.
To to the structural part only requires epoxy between the magnet and the rotor.  To do the protection part only requires a coating.  You could save yourself from using an extra gallon of it that won't help the protection any more.  Actually, it could work against you.  Epoxy is an insulator and magnets do get hot.  Ferrites are not very tolerant of high temperatures so allowing them to cool with airflow close to the surface should help.  At the bottom of a pool of epoxy they won't get that.

I haven't seen a WT stator project done with phenolic plate in a long time.  It's awful stuff - I can't believe you're using it.  Bad enough that it's worth repeating like a broken record: dust masks are obligatory when working with it.

Your target is modest with the Sav, so I don't see a benefit in over-thinking it.  All the calculations in the world won't change the result you get from your test coil.
It will be easiest to wind your first coil with 22GA wire so why not start with that, unless you want to save your short supply?  Measure voltage open-circuit first, and you can scale that number with the number of turns you get from other gauges of wire (less turns fit). 

Then experiment with loads on the coil.
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #24 on: July 11, 2019, 08:38:29 AM »
SparWeb, thanks for the reply and thanks again for all the calculations you made on this build way backwhen I first started this.

The magnets have already been glued to the rotor plates with JB weld. I glued them to the cleaned raw steel, masked them and then painted the rotor. Don't ask me why I didn't just paint both magnets and rotor at the same time... I guess I liked the way it looked.

My understanding is ferrite magnets are very corrosion resistant in their raw state, unlike neo's. I wasn't considering potting them. From research done on Proven they did not pot the ferrite magnets in their machines and it appears the magnets were left in raw state and not even painted. Chris Olson did a ferrite magnet PMA and did not pot the magnets, he did however give everything a coat of red primer. I've also viewed a ferrite magnet axial flux PMA made by Hugh Piggot that did not appear to have anything but a coat of paint on the magnets. I could give them a shot of paint and feel they would be okay. The magnets used were purchased 6-7 years ago and have been sitting in my garage out in the open. Here in Florida everything rusts from the high humidity but they still look the same as the day I bought them.

You're right about using a dust mask when working with phenolic, especially fiberglass/epoxy G10. I worked at a plastics only machine shop (sales) for many years and saw the precautions the machinist took. When sawing, drilling G10 your hands will itch for a day after handling the material.

I'll just try a few different sizes of wire for the test coil and see how the winding goes. May try a two in hand approach with the 22 AWG. I can wind several different coils and test them out at the same time.

Thanks,
CM
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #25 on: July 11, 2019, 03:46:22 PM »
 I wound three test coils today. I'm pleased with the way they came out, so much easier winding with the half round molding on the ends. The molding is just flexible enough to hold the wire tight and allows the wire to lay flat against the core.

All were done as one layer, I have no idea if this is enough copper per coil or not. Am I correct that once open circuit voltage is measured I can assume double that result if two layers are wound?

The spokes holding the core are 1/8" thick. The 15 AWG and 17 AWG wire sits flush or slightly below the top surface of the spoke. The 20 AWG wire I could probably run a second layer and stay flush with the top of the spoke. My thought is once I have wire size and layers determined if the winding sits above the top surface of the spoke I will add a layer of spacer material to bring the level of the spoke flush with the wire. Once that is done a 1/32 sheet of G10 material will be used to cover the coils and will be glued to the spokes to provide protection for the stator surface.

Here are the test coils;

11987-0

11988-1

11989-2

11990-3

This is the 17 AWG coil.

11991-4

This is the 20 AWG coil

Thanks,
CM
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #26 on: July 11, 2019, 03:56:57 PM »
Here is the material that will cover the coils and top of stator when all winding has been completed.

This is 1/32" G10. If I need to add a spacer to the spokes balsa wood sheet comes to mind. It's easy to cut, inexpensive and comes in many thicknesses. It doesn't need to add structural strength.

The G10 will be epoxied to the top of the spokes and held in place with smallish ferrite magnets while the epoxy sets.

11992-0

11993-1

Here you can see how ridged the material is. Held perpendicular there is little bending.

Thanks,
CM
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MagnetJuice

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Re: Dual Rotor Toroid Core PMA build
« Reply #27 on: July 11, 2019, 06:33:31 PM »
Looking good Craig! The way to find how many turns per coil you need is to find out how much voltage is produced by the test coil at a given RPM. It goes by turns. If 17 turns produce 1 volt, 34 turns will produce 2 volts. The harder part will be determining what will be the RPM that the alternator will start charging the battery.

You will have to decide if you want a HAWT or a VAWT, then you will have to match the size of the blades to the expected power of the alternator at a certain speed.

I did some calculations and found that your alternator could produce 500 to 600 watts. The RPM will be determined by the number of turns of wire that you have in your coils.

As for the wire gauge to use, the ideal would be the thickest that you can get in the space that you have. That way if the windmill is hit by strong winds, the stator don't burn. And speaking of burning, you should keep any flammable materials away from the stator, like balsa wood for example. If you need a spacer, you can use Polypropylene, Polyethylene or Polycarbonate. Any of those thermoplastics can tolerate a fair amount of heat. What about that flexible molding, can they tolerate heat?, because those coils are going to get hot.

Ed
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #28 on: July 11, 2019, 09:38:46 PM »
Yikes, you're right, there will be considerable heat. I know that and factored it in for the G10 (150C same as polyester resin) and for the JB Weld (260C) even the Nomex 410 insulation (200C) but didn't think about the plastic molding. This could be a problem, I'll need to find a data sheet for it or do some testing myself. Could always pop a piece in the oven and see what happens. Will need to do this before moving on with coil testing.

Thanks for the heads up and reminding me to be aware of heat considerations, just the reason I'm putting this out here.

Much appreciation!
CM
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MagnetJuice

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Re: Dual Rotor Toroid Core PMA build
« Reply #29 on: July 11, 2019, 11:14:59 PM »
Here are some choices for high temperature materials for the edge molding, just in case that the one you have won't tolerate the heat.

https://www.northernbrewer.com/products/3-8-id-silicone-high-temp-tubing

http://www.hps-siliconehoses.com/three-eight-inch-silicone-hose-coupler-reducer-elbow-tube-silicon-hoses.html

https://shop.advanceautoparts.com/p/walker-high-temperature-exhaust-hose-sold-by-each-35583/18370502-P

https://www.amazon.com/Walker-36344-High-Temperature-Exhaust/dp/B001BFLJI0

Most of these hoses are made using silicone rubber, so the only way to glue it will be using silicone rubber from a tube. That withstands over 400F. If you end up using something like this, you probably have to split it in half. To attach it, put a bead of silicone rubber on the edge of the stator, then place the hose over the glue and hold it in place and let it set for 24 hours.

Or maybe someone else can suggest a better idea. I'm just a part of a team here.  :)

Ed
« Last Edit: July 12, 2019, 12:17:32 AM by MagnetJuice »
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #30 on: July 12, 2019, 10:41:47 AM »
MagnetJuice,

Thank you for the recommendations. I believe I lucked out with the molding I used. According to the manufacturer this material is a "special formula" polyurethane material with a maximum structural working temperature of 300F.

I did an oven test to see what would happen.

  • Placed six inch piece of material on aluminum foil, put this in cold oven and set temp to 300F.
    * Examined material when oven temp reached 300F. No change in material characteristics.
  • Set over timer to 10 minutes, left temperature at 300F.
    * Examined material after 10 minutes. Very hot to hold in bare hands. Material was not sticky, pull test and compression test (pinching) did not notice a change in material characteristics. No outgassing.
  • Set over timer to 10 minutes, raised temperature to 350F.
    * Examined material after 10 minutes. Could not hold material in bare hands. Material was not sticky, characteristics unchanged, only difference was slight discoloration (darkening). No outgassing.

I've based my temperature considerations on the use of polyester resin by Hugh Piggot. Polyester has a maximum service temperature of around 300F. As long as I stay in this range or above I'm hoping to not have a material failure due to excessive heat.

I'm going to roll the dice and continue on with this material. This however was just a short test, how it will hold up in the long run is anyone's guess. It's all experimental at this point and lessons will need to be learned along the way.

...kind of how I like it... keeps the journey interesting.

Thanks again,
CM
« Last Edit: July 12, 2019, 10:58:10 AM by CraigM »
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MagnetJuice

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Re: Dual Rotor Toroid Core PMA build
« Reply #31 on: July 12, 2019, 10:54:29 AM »
That is good news; it saves you some work and gives you peace of mind.

Can you tell us where you got that molding and what is called? Just in case that someone else needs to use something like that.

Ed
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CraigM

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Re: Dual Rotor Toroid Core PMA build
« Reply #32 on: July 12, 2019, 11:02:15 AM »
MagnetJuice,

I purchased the material through Amazon. Here is the manufactures web site https://flexiblemouldingconcepts.com/

Thanks,
CM
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