Radial Flux Generator Project

[Flux]

Not addressed to me but I will comment from the experience i have.

This wire method is a very old one and was used in early Gramme ring and other machines. Ideally the wire needs to be low loss material and annealed, the oxidation from annealing will provide sufficient insulation.  Probably the soft iron wire used by florists will be as good as you can get easily.

Other wires such as mig wire will be hard drawn and include things that don't give the best results but still it will work fairly well in this application. The copper coating doesn't help the eddy issue but even then the contact area is small and the emf is very low, I doubt that it would be a real problem.

Annealing it in a fire would improve permeability and give better insulation.

I doubt that anyone specifically makes wire from low hysteresis loss materials so you have to take what you get. Soft annealed iron wire will be your best bet.

Flux

[Ovais]

Thanks Oztules.

How much thick is the wire backing in Seeley motors? And what type of wire has been used?


Ovais

[artv]

Flux........as long as the wire has mgnetic attraction..and it dosen't leak out the other side............would this be sufficent...artv

[tecker]

The reversal of field is too slow .Bailing wire or the like will start good but develops a field after a while that kinda  is the same polarity as the magnet and shuts down the core and attraction of one pole after the core has been working awhile  there's little predictability of how it will balance out but the losses are obvious . Welding wire is good it's about right really and silicon welding wire is available. The copper coat is a good magnetic separator.

[ChrisOlson]

I ran my radial generator this morning on my new test stand I built and its performance isn't as bad as I thought it would be.  I ran it at 8.8 amps @ 56 volts for 30 minutes @ 330 rpm and it got hot enough that a person would not want to touch it (only wound with AWG 18 wire).  The temperature of the core got up to 159 degrees after 30 minutes with no forced air cooling.

It's power efficiency isn't all that great - it figures out to about 39%, rectified to DC.  I ran some tests with a single rotor axial with just a blank steel plate on one side of the stator and that doesn't work all that great either.  It's easy enough to get the cut-in voltage at the right rpm but it doesn't put out any amps unless I spin it to 600 rpm.

So I need to build a new core for my radial.  I don't know what that's going to be yet.
--
Chris

[joestue]

The copper coat is a good magnetic separator.

copper is just an eddy current brake when it comes to a magnetic core, furthermore since its not going to corrode, and the oxide flakes off it is about the worst thing you can put in a core. there are various methods to create a strong oxide coat that will be "good" enough for this application. its also possible to pull the carbon out of the wire if you have access to a kiln, or you could wind up the steel with a layer of epoxy saturated tape every other layer.

 Chris, did you run it with no load to determine if the core creates any significant drag?

[dlenox]

Chris,

Don't remember what your original goals/parameters were, but since you have magnetic flux bleeding through the core, why not turn this into a dual rotor by adding an additional rotor w/magnets on the outside of the core?

There looks to be enough material in the core to bolt it through it's face instead of clamping around outside perimeter, and it would make use of the current core by only changing the holding mechanism.

Just a thought...

I just remembered that a long time ago Hughes Aircraft made counter rotating props on some experimental engine.  I'd be a lot of work but using some planetary gears would accomplish this, possibly with a plus of speeding up the rpm of the magnets with the same prop speed.  In addition the counter-rotation of the rotors cancel out any gyroscopic forces.  It sounds like an interesting dream.

Dan Lenox

[ChrisOlson]

Chris, did you run it with no load to determine if the core creates any significant drag?

Yes.  A whopping 270 watts @ 330 rpm.
--
Chris

[ChrisOlson]

Don't remember what your original goals/parameters were, but since you have magnetic flux bleeding through the core, why not turn this into a dual rotor by adding an additional rotor w/magnets on the outside of the core?

Dan,

I don't know how I'd get adequate air flow thru such a thing to cool it properly.  It would be easy enough to mount an external rotor ring and swing magnets outside an air core stator - and to design a fan blade into the rotor where the blades support the outer magnet ring.  But making that an easy thing for the average homebuilder to make would not be so easy to do.

One of goals with this project was to design a compact, efficient radial generator that the a homebuilder with a lathe and good build skills could make.  And that's one reason I hesitate to go to a laser cut electrical steel laminated core.
--
Chris

[willib]

Hi Oz , your photo clearly shows that the magnetic material , the wire in this case , that is behind the coils , and opposite the magnets , is not moving with magnetic poles as the alternator spins.

So therefore the second disk on an axial flux machine , which sometimes does not have magnets on it , also does not have to spin .

I was sometimes questioning that premiss , that the second disk has to spin with the magnetic poles, because the magnetic flux will move along the path of the magnets energizing the coils as they pass. and probably could not care less if the second disk was moving or not..

[Flux]

This is a misconception. The flux couldn't care less whether the disc spins or not. The flux will still return in the same way whether it spins or not.

If the disc rotates then the flux is stationary with respect to the dics and no eddy currents can be induced in it.

As soom as you make the disc stationary then the moving flux will cut the low resistivity steel and induce eddy currents in it. The cure is to laminate the fixed disc, that removes eddy loss but still leaves you the hysteresis loss.

The reason the core is wound from wire is purely to break the eddy loop, in every other respect a solid disc would be much superior. The best core in this case is a high permeability low hystaersis loss tape but in view of the rather low flux density a bundle of iron wire is adequate, you just need a bit more of it to make up for the spacing factor and loss of iron.

The spinning solid steel disc is beter magnetically and doesn't suffer any form of iron loss but it means that the coils can't be stuck to the core.This adds a second air gap and makes the cooling of the coils much less effective.

In anything other than a wind generator the low level hysteresis loss is not important so the air gap machines are not so necessary. With wind the core loss can be made low with fixed cores if the core material is good and you aviod high flux densities. The common slotted motor type core is not so good in this respect but smooth cored machines with coils in the air gap are a good compromise between core loss, cooling and mechanical complexity.

All depends on how much you value a few watts in low winds which approach you adopt.

Flux

[clintonbriley]

How much does it matter which direction the laminates are stacked? 
Clint

[jeraklidis]

Chris can you give me the dimensions of the design and I'll try to see if I can come up with something in this program I have?

[jeraklidis]

How much does it matter which direction the laminates are stacked? 
Clint

It matters a lot...

[ChrisOlson]

Chris can you give me the dimensions of the design and I'll try to see if I can come up with something in this program I have?

The core is 10.2" OD, 7.550" ID, 1.950" thick.

The rotor measures 7.500" from flat to flat on opposite poles, and going from corner to corner on the magnets on opposite poles is 7.540" so there's .005" between the corners of the magnets and the core as it rotates.  The magnets are N42, 11,200 gauss, 1" wide x 2" long x .5" thick.
--
Chris

[jeraklidis]

uhhh those were not dimensions... I had to estimate from the picture... Disclaimer: I don't know if this is correct nor do I take any responsibility in your interpretation of this...

sorry for the quality it wouldn't accept my bmp file.

[jeraklidis]

btw I had to use laminations since there was no such thing as epoxy iron shavings mix hahaha.... looking at it maybe you should use a non ferrous ring on the outside. I made the inside ring .125 thick as you can see its very saturated I'd make it thicker.... your shoe design needs some work as well but its a good visual to start with.

[tecker]

Ok I can tell your not looking forward to removing the magnets from the rotor and your  at a stand still on the current stator . I 'll kick in one more time here . I f you cope the core segments straight and wind 18 coils the same direction I think you'll be in the park with this stator form . The reason is the current released from each coil will buck the on comming magnet and control the heat buildup . You'll have to as you said earlier dampen the cog with a good sized blade set and hub however  it will work . May be three strands of 18 . Four  20s would be easier to wind but either will be good for 40 amps per phase and the voltage will be high for a big blade set . 

[ChrisOlson]

Ok I can tell your not looking forward to removing the magnets from the rotor and your  at a stand still on the current stator

I've been pretty busy with other things.  I bought a 1 kW solar array and had to get that installed, and then it rains every time I try to do anything outside.

After my findings from running this generator I've decided I'm going to pour another stator core using my steel mold I made.  That mold will make it 1" bigger OD.  Then use a stainless steel ring around it instead of mild steel, and cut 36 slots in it instead of 18.  It's not a lot of work to make a core so I think that would be worth a try.

And you're right on the magnets - they would be hard to get off.  I just superglued them on pins for testing and I tried to get one off the other day and it was darn near impossible.  I tapped it with a rubber hammer to break the superglue bond but I couldn't pull it off the pin.  The pins would have to be driven out to the inside of the rotor so the magnets could be slid off one side of it - and as soon as you do that the magnet that's freed suddenly flips over onto one of the adjacent poles and makes it really hard to slide off.

If this thing eventually works, the magnets are going to have to be removed anyway to JB Weld them to the rotor - and I don't look forward to that project.
--
Chris

[ghurd]

Why stainless?
If it is related to eddy currents, it will not help.

Cut the slots at an angle and the cogging will be reduced.
G-

[jeraklidis]

Why stainless?
If it is related to eddy currents, it will not help.

Cut the slots at an angle and the cogging will be reduced.
G-

Its best to work out the design details first. Skewing a stator or skewing magnets still induce losses and make the design harder to produce. I would first try to find a High LCM (pole/slot) and check if the forces are balanced in the stator at which ever Hz you'll be running it at. Small cogging is good it can save part life since it takes a certain cut in speed to get things going. Most stainless is not magnetic. As you can see in the pic there are strong flux line around the holes. Anything ferrous around that area will interrupt the magnetic circuit that you are trying to create. Cogging isn't the issue flux and saturation is. At certain parts you want saturation to occur and at other parts you don't. I say keep going this project is interesting...

[ghurd]

Why stainless?
If it is related to eddy currents, it will not help.

Cut the slots at an angle and the cogging will be reduced.
G-

Its best to work out the design details first. Skewing a stator or skewing magnets still induce losses and make the design harder to produce. I would first try to find a High LCM (pole/slot) and check if the forces are balanced in the stator at which ever Hz you'll be running it at. Small cogging is good it can save part life since it takes a certain cut in speed to get things going. Most stainless is not magnetic. As you can see in the pic there are strong flux line around the holes. Anything ferrous around that area will interrupt the magnetic circuit that you are trying to create. Cogging isn't the issue flux and saturation is. At certain parts you want saturation to occur and at other parts you don't. I say keep going this project is interesting...

Uh... sure... you bet.

In this one, the difference between SS or regular steel ring is not going to noticeably effect the cogging (probably) or the eddy currents.

Skewing that stator is pretty easy.  Even I could do that.

[Ungrounded Lightning Rod]

Why stainless?
If it is related to eddy currents, it will not help.

Cut the slots at an angle and the cogging will be reduced.
G-

Its best to work out the design details first. Skewing a stator or skewing magnets still induce losses and make the design harder to produce. I would first try to find a High LCM (pole/slot) and check if the forces are balanced in the stator at which ever Hz you'll be running it at. Small cogging is good it can save part life since it takes a certain cut in speed to get things going. Most stainless is not magnetic. As you can see in the pic there are strong flux line around the holes. Anything ferrous around that area will interrupt the magnetic circuit that you are trying to create. Cogging isn't the issue flux and saturation is. At certain parts you want saturation to occur and at other parts you don't. I say keep going this project is interesting...

Uh... sure... you bet.

In this one, the difference between SS or regular steel ring is not going to noticeably effect the cogging (probably) or the eddy currents.

Skewing that stator is pretty easy.  Even I could do that.

Actually it will raise the eddy currents, since the mag field that escapes the core inside the stainless ring will all try to penetrate the ring - and make eddy currents as it's dragged through.  With iron most of that field would only go partway through, resulting in less eddy current.

[ghurd]

Why stainless?
If it is related to eddy currents, it will not help.

Cut the slots at an angle and the cogging will be reduced.
G-

Its best to work out the design details first. Skewing a stator or skewing magnets still induce losses and make the design harder to produce. I would first try to find a High LCM (pole/slot) and check if the forces are balanced in the stator at which ever Hz you'll be running it at. Small cogging is good it can save part life since it takes a certain cut in speed to get things going. Most stainless is not magnetic. As you can see in the pic there are strong flux line around the holes. Anything ferrous around that area will interrupt the magnetic circuit that you are trying to create. Cogging isn't the issue flux and saturation is. At certain parts you want saturation to occur and at other parts you don't. I say keep going this project is interesting...

Uh... sure... you bet.

In this one, the difference between SS or regular steel ring is not going to noticeably effect the cogging (probably) or the eddy currents.

Skewing that stator is pretty easy.  Even I could do that.

Actually it will raise the eddy currents, since the mag field that escapes the core inside the stainless ring will all try to penetrate the ring - and make eddy currents as it's dragged through.  With iron most of that field would only go partway through, resulting in less eddy current.

I must have misunderstood something somewhere.  Or we said the same thing.
The core is surrounded by a ring of SS or RS (Regular S)?

The core of 'mixed goop' is not sufficient to contain the flux with an iron ring around the OD of the core to keep it from supporting a wrench.
If enough flux is getting past a core that long, with those magnet lengths, I do not see the ring around the core as being SS or RS all that important.

Now I am confused.
G-

[joestue]

20$ says the stainless steel band will suck up significantly less eddy current than the steel one will, on the order of 30% or less.
reason being that the soft steel band sucks up most of the flux, and eddy current loss follows flux squared, also the resistance of stainless is higher than that of steel.

that being said I wouldn't wrap a steel band around it in the first place, but rather bolt it to.. something.

[ChrisOlson]

20$ says the stainless steel band will suck up significantly less eddy current than the steel one will, on the order of 30% or less.
reason being that the soft steel band sucks up most of the flux, and eddy current loss follows flux squared, also the resistance of stainless is higher than that of steel.

I don't know what to think.  The experts aren't agreeing here.

I did a little test after I read all this stuff.  I put a neo mag on a sheet of 1/8" stainless.  Using a completely unscientific method of sticking a 1" bolt to the other side of the sheet and pulling it off, I determined that sticking the same magnet to a sheet of 11 gauge A36 and using the same bolt that it takes more effort to pull the bolt off the bottom of the sheet of mild steel.

Test #2 - I can easily slide the magnet quickly across the sheet of stainless and I can't feel any significant "drag" from eddy currents.  It's impossible to slide that magnet back and forth on the sheet of 11 gauge A36.  Sliding that same magnet quickly across a sheet of 1/4 aluminum I can definitely feel the drag from eddy currents in the aluminum sheet.

I don't know what any of this means, but it would appear to me that flux goes thru mild steel much easier than stainless steel.

I cleaned all this stuff up before I played with the magnet and I still got metal filings from someplace stuck to my new magnet, dang it anyway.
--
Chris

[frepdx]

After my findings from running this generator I've decided I'm going to pour another stator core using my steel mold I made.  That mold will make it 1" bigger OD.  Then use a stainless steel ring around it instead of mild steel ...

you could also mold a fiberglass strap/mount instead of stainless if you get a lot of flux leakage.

uhhh those were not dimensions... I had to estimate from the picture... Disclaimer: I don't know if this is correct nor do I take any responsibility in your interpretation of this...

how did you model the permeability of the resin/iron? Your model doesn't show much flux leakage, but it was enough to hold a wrench.

[jeraklidis]

I ran some more simulations. Since a lot rides on the permeability of this epoxy a lot can change BUT after some trials my answer is "I would use aluminum to hold the stator". 300 series stainless contains nickel and is not magnetic but the 400 series do not contain nickel so they are magnetic. I ran a simulation with aluminum wrapped around the outside and even if you put your wrench on the outside pending the thickness (not that thick) of the Aluminum it won't stick. I ran 416 and its very permeable and the flux runs right through. When I put an aluminum housing around the stator the flux lines kept in the right direction(even with another iron core around the aluminum core).

In reference to who ever was talking about cogging there are MANY ways other then skewing to reduce cogging a few others are

Magnet Shape or Tooth shape
or
bifurcation of the tooth

I would REALLY consider working a different pole slot combo with a high LCM if you are worried about cogging.

[Flux]

I am not sure that holding this thing is the big issue that is going to kill the project.

If there is enough flux to seriously cause these problems at the back of the core you will have other much bigger issues. Non conducting materials such as glass epoxy will mount it ok. If you must use metal then crudely laminated mild steel ( plates up to 3/32 thick should contain the flux with little eddy loss.

Non laminated metal will cause some loss but if the core is that bad you might as well leave it out. The higher the metal resistivity the better and in that respect stainless may be best but cast iron may also work.

Ignore this problem for now, hold it in wood blocks or something if need be and see where you go from there. If it looks promising in other ways then think about the mounting issue. I doubt that it is any worse than a lot of single rotor axials, I really can't see a core with that much leakage being much good in other respects so you might as well check these problems first.

My immediate thought is that if the core is this bad you would do better to make bigger slots for more copper and cut the copper loss.At present you have very little winding space. best not to generate copper loss than cool it with a howling gale.

Flux

[ChrisOlson]

My immediate thought is that if the core is this bad you would do better to make bigger slots for more copper and cut the copper loss.At present you have very little winding space. best not to generate copper loss than cool it with a howling gale.

This makes sense.  I could make a plywood mount for it and glue the core to the plywood with fiberglass resin or something to see if I can get the core material to work at all.  And Ed Lenz told me about the same thing on the copper - with the 18 coil layout I got as much wire in the winding heads as I do in the legs.  Going to a 36 slot core reduces the amount of wire in the heads and will give much better performance than the 18 coil arrangement.

It's a relatively simple task to make a core and drill it and slot it on the drill press.  Ed Lenz once built a laminated core for an axial out of plain sheet metal and cardboard and it worked.  So I'm thinking about ways to do that too.
--
Chris

[DragonFly III]

Plain sheet metal and cardboard?

[ghurd]

Plain sheet metal and cardboard?

Here-
http://www.windstuffnow.com/main/alt_from_scratch.htm

G-

[DragonFly III]

Thanks Ghurd, I have seen that before.