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Forum Index : Other Stuff : axial flux FEMM animation
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Thanks for the alert Oztules. It's certainly flattering to know that Hugh Piggott considers it useful enough to be mentioned on his front page. But let me reassure you that I won't let the new-found glory get to my head (a lot). However, if you'd insist on calling me 'sir', I wouldn't object to that, of course. Peter. |
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| jimovonz Newbie  Joined: 09/04/2007 Location: Posts: 7 |
Peter, I have done a number of simulations along the same lines and and even delved into the LUA scripting to automate a large portion of the simulation of axial alts. One point of interest I have found is in comparing dual magnet rotors to single magnet rotors (with a blank disc for return path) is that the average flux in the gap for the single magnet rotor is significantly more than the half you might expect compared to the dual. In fact it is much closer to 2/3 for the typical 2x1x1/2" magnets on 1/2" thick disc with a 1/2" gap. This would imply that you could achieve 2/3 the output with 1/2 the magnets. Given that the magnets are typically the most expensive componenet for your average DIY'er it may be a more cost effective solution in some cases. Some futher rough calcs indicate that a single (magnet) rotor using 16 magnets rather than the typical 24 magnet in a dual magnet rotor should give a 20% increased output. Of course this would require more metal (1/3 larger diameter discs) and 1/3 more copper (4 coils per phase instead of 3). With out calculating some actual quantities and values, I'm not sure where the break even point would be but I found it interesting anyway  |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi jiomovonz, I am building a new dual rotor AxFx alternator. It is interesting that the FEMM simulation gives a 16% increase in avereage flux. This may be a result of the complex field from the rectangular bar magnets. I am using 2"x1/2" round disks. I have almost finished my coil test rig. I will initially be using only one magnet ring, and a blank iron plate return path. I was planninng on doubling the emf to guage the dual magnet ring oputput. It seems that I may actually need to test with the dual magnet rings. Re the costings for magnets. To go to the bother of making an alternator and not using 2 magnet rings is not really plausible. My magnets mentioned above cost me AU$12 each. The $144 for a second magnet ring is money well spent, as This efectively doubles the alternator max power. This will translate in my case to a higher alternator efficiency. When I sell power for 64c/kWhr, the small additional magnet cost will not take long to be paid off. Gordon. become more energy aware |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Jim, In the past I have simulated exactly the same as you ( http://picasaweb.google.com/lh/photo/7NDojUFBLhKs9APJhLiKPQ? feat=directlink. In my experience magnetic flux drops to 75%, so voltage will drop to 75% too (ceteris paribus). This means power output will drop to about 56%, nearly half. Half the magnets yields about half the power. No gain to be had here from going to magnets on only one rotor disc. I wholeheartedly agree with Gordon; magnets and copper wire are the heart of any generator. Skimping on either is not smart. I highly value my time and effort and wouldn't want to waste it on projects that will end up mediocre. I always try to do a perfect job, or at least to come as near as possible as I can. Mediocrity is not an option. BTW, it's nice to see you are playing with FEMM too. It's a splendid (yet simple) tool that's vastly underapplied in this field. Peter. |
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| Florin Newbie Joined: 28/04/2009 Location: RomaniaPosts: 10 |
Hello. I am from Romania and I read many times this forum and the web page. Sorry for my english. I make a script in lua for simulating induction in air gap. After unzip the file run femm and then from File->Open Lua Script -> open Path/gen_eol/scripturi/script.lua In folder Path/gen_eol/rezultate/ find B-H.txt and geometrie.txt and in folder Path/gen_eol/imagini find graphical rezult of simulation. With this images can make a animated gif and with B-H.txt can make a graphic characteristic for variations B/air_gap or/and H/air_gap. 2009-04-28_232333_gen_eol.zip |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Hello Florin, Interesting solution you've found to compensate for the end-effects on your model by putting half-sized magnets at the ends. Will use that idea myself next time! 
I noticed you generate the entire geometry in the script; impressive, but a lot of work. I prefer to make the drawing in CAD (save as .DXF) and use that as the basis for simulations. Much quicker, less error-prone, and it's easy to do complicated geometries that way (e.g. an induction motor). Peter. |
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| Florin Newbie Joined: 28/04/2009 Location: RomaniaPosts: 10 |
Hello Peter, I make the geometry with the script because I wish to be parametric and more easy for peoples who not know to work with femm. In input_data.lua they can make changes to the materials (e.g. the magnet or the disc steel). When I having time I change the script for putting coil and make the translation horizontal for calculating emf (not it's impossible but not easy). I used femm for determination the induction in air gap for my windmill /My Page (the page is only in my language romanian for the momment). |
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| jimovonz Newbie Joined: 09/04/2007 Location: Posts: 7 |
Florin, You have taken much the same path as I did. My model is also built directly in lua based on a parameter file. Not being familiar with any CAD software, I got sick of using the FEMM interface to build all the different models I wanted to test. I use mine to output the 2D flux along select paths through the the air gap on multiple views. I use these in another program (written in c) that interpolates a full 3D representation of the flux between the magnets. Currently the model caters for rectangular, round and wedge shaped magnets. It can also handle single rotor, dual rotor, dual rotor with magnets on one side only in various dimensions. The same program builds a 3d model of a coil based on the specification of the central core(hole). It essentially 'wraps' wire around the central core until the specified number of turns is reached or the space available is full. It then simulates the movement of the flux relative to the coil and using FEA derrives an EMF profile. It's all a work in progress an has soaked up a significant amount of my time. Some of these features are not fully implemented and currently require a significant manual effort to complete. There are also some bugs that give nonsense output in some configurations... |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I admire the simulation approach, and this may be useful when I wish to explore other ideas. I still found that making a prototype that allowed adjustment to the major variables, except the magnets, gave me actual numbers to work with. You cannot always make the best computer model. Gordon. become more energy aware |
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| jimovonz Newbie Joined: 09/04/2007 Location: Posts: 7 |
Gordon, I agree. I have made 4 axial flux dual rotor alts and have always performed the 'real world' tests to confirm I'm on the right track. I find that the process of creating an accurate (as possible!) simulation helps me develop my understanding by forcing me to consider the less obvious interactions between components. It also allows me to more quickly see the merit (or lack there of) of the many ideas that come to me (far too many to try for real in the limited time I have). Certainly no substitute for real world 'doing'. |
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| Sara Myrphy Newbie Joined: 12/07/2011 Location: Posts: 1 |
It sure is nice when someone does work you have been wondering about. I have been contemplating a 'wave wound' axial flux alternator. This style of winding should give twice as many 'cuts' of the magnetic field as 'simple coils' and allow a thinner stator. This all should result in more voltage at lower speeds. |
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