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Dinges
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Posted: 07 January 2009 at 1:42am | IP Logged Quote Dinges

So I've been playing with FEMM a little more.

Decided to make an animation of the changing magnetic fieldlines as a function of airgap for the axial flux generators. A small, low-resolution sample is shown below. Even this one clearly shows the changing flux lines and increasing leakage flux and diminishing flux density as the airgap increases.



Links to the complete animations can be found below. I like the 2nd one better because of the absence of a sudden transition in the loop, but the price for that is a much larger file. Click on the magnifying glass (near top-right of the image) to start loading the file and viewing the animation.

http://picasaweb.google.com/motorconversion/AxialFluxFEMMSim ulations#5288197761856843090 (warning, 7MB filesize)

http://picasaweb.google.com/motorconversion/AxialFluxFEMMSim ulations#5288199885557074706 (warning, 15MB filesize)

The technical details of the generator are: steel plates 10mm thick AISI-1010. Magnets N40 2"x1"x.5", viewed 'head on' (2" dimension into the screen). Spacing between magnets is 25mm (one magnet width). Minimum airgap 1mm, maximum airgap 27mm.

Hopefully others in this forum will find these animations useful too in visualizing and understanding the magnetic fields of axial flux generators.

Peter.




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oztules
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Posted: 07 January 2009 at 2:24am | IP Logged Quote oztules

Very very nice Mr Dingesman.

It is nice to see that there is a reasonable winding window there for good flux, wire room and mechanical strength.

A well spent 15mb of bandwidth. I have henceforth stolen a copy as a reference for my next supergenerator.

It certainly is good to see what happens rather than guessing. Since you introduced me to your Femms, I can now pretty well guess what the fields will do and look like, but without your initial efforts to get me on track, I would never have gotten to that understanding...just couldn't get it.

Thanks a bunch


........oztules

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GWatPE
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Posted: 07 January 2009 at 7:27am | IP Logged Quote GWatPE

Hi dinges,

nice work!

Would have been good to have this sort of tool when I designed my AxFx motor, that I use for my AxFx mill. iron filings, and a hall effect sensor had to do, for me.

Gordon.

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Dinges
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Posted: 07 January 2009 at 1:51pm | IP Logged Quote Dinges

Thanks, Oztules and Gordon.

As I said, I hope it's of help to others for visualizing what normally remains invisible with these generators. It actually opened my eyes to something I hadn't fully realized myself yet. Took 6 hours of numbercrunching by the PC (P4/2.4GHz), but I figure the result is worth it.

Peter.
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wdyasq
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Posted: 07 January 2009 at 2:08pm | IP Logged Quote wdyasq

I hate it when I need to say nice things about a Dutchman.

So, how many think he stole that file?

Ron

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oztules
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Posted: 07 January 2009 at 3:19pm | IP Logged Quote oztules

Ditto Ron....

I only said nice things in case I need a Femm done myself.... he knows I'm hopeless


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philb
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Posted: 08 January 2009 at 8:14am | IP Logged Quote philb

Thanks Peter,
IMHO, it was worth 6 hours. The file is going into my archives.
Visualizing the invisible is everything.

Now I'm thinking about my last mill. Maybe the coils could have been a bit wider and thicker...hmmm.



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vawtman
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Posted: 08 January 2009 at 11:05am | IP Logged Quote vawtman

Nice work Peter and thanks once again for your help with mine
One can actually predict the future for a turbine with these simulations.
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Gizmo
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Posted: 08 January 2009 at 2:15pm | IP Logged Quote Gizmo

So long as the magnet pole across the coil gap is closer than the neighboring magnets pole, most of the flux will go across the coil gap. A taller ( more distance between its poles ) magnet also will be more inclined to throw its flux across the coil gap, which is one reason 2 or more stacked magnets work better.

I wonder what gain would be had if, instead of two stacked magnets, we used one magnet and one same sized block of steel under it. If it means it will throw ( for want of a better word ) its flux further, for little extra cost, it could be worth considering.

Glenn

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Dinges
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Posted: 08 January 2009 at 9:00pm | IP Logged Quote Dinges

Glenn,

I think I know what you're getting at but if you could make a sketch of it I'll try to give simulating it a run. Now that the LUA script is working properly it has taken most of the hard work out of it. All that's left now is dumb work...

In the mean time, to prove Ron wrong, I've made another one of the case without steel backing plates. It's interesting to see how, as airgap increases, the flux lines initially bend back to the same magnet (shorting over the outside of one magnet) but then later, as airgap becomes larger, start shorting to the neighbour magnets. It's also immediately obvious that the flux densities are much lower than the case with steel backing plates.



The detailed animation can be found here (warning, 19MB filesize):
http://picasaweb.google.com/motorconversion/AxialFluxFEMMSim ulations#5288870849377406322

Peter.
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Posted: 08 January 2009 at 9:20pm | IP Logged Quote Gizmo

This is what I'm thinking.

Each magnet is on a steel pillar, to lift it clear of the rotor plates. The magnet path through the steel rotor is still complete, if slightly longer. The hope is a larger gap could be achieved with the same flux density. It would be interresting to see what FEM has to say. If adding steel pillars means a increased flux density or increased air gap, than its a cheaper option that stacked magnets and better power than single magnets flat against the rotor face.

See what I'm getting at.

Glenn


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Posted: 08 January 2009 at 9:32pm | IP Logged Quote whiskey

Over the Christmas period I got called to a 6Kw Proven wind turbine installation that needed help. This is a down wind machine and relatively slow speed.

The magnetic rotor was approx 2 1/2ft in diameter and its magnets were fixed horizontal, not vertical like most home brew wind turbines are built. The magnets were approx 150mm long and 50mm wide and 20mm deep. They may have been made by stacking two magnets together, evidence of some 'goop' was visible along the mid (10mm) point on the magnets. It has 12 poles (there was a surprise) and the coils were at embedded in a hard plastic like mouled material and was at least 50mm thick. The air gap was very wide, 5mm at least.

I believe Proven use a Toroid type coil for high efficiency. I would agree with that arrangement if it were not for the pictures I have been sent of burnt out coils from their machines. Cooling may be a problem, or the blades may have a control problem. For those who want to research Toroids. have a looksee here http://hyperphysics.phy-astr.gsu.edu/Hbase/magnetic/toroid.h tml

Some footage of the machine sitting on its shipping pallet exists and I will look into extracting some pictures of the magnetic rotor is any of you want to see it.


Whiskey

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