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Forum Index : Windmills : Yet another axial
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
I've been drawing up plans for a small axial flux alternator. I was inspired by recent posts about the price rises in rare earth magnets, and Hugh's comments in this thread about the advantages of ceramics compared to the more powerfull rare earth magnets. My last axial flux build was based on the 50mm wide 12mm thick rare earth magnets. Its unfinished, cause it weighs a tonne and I've got nothing big enough to drive it, it can wait till I get some land and can put up a big turbine. Here's the thread about that build. I searched the magnet suppliers to see what was available in ceramic, and found this little ferrite magnet, its 22mm diameter, 25mm high, 1800 gauss, and $1.10 each. Of all the ferrites, its one of the strongest for its price, due to its long length. So I've ordered 64 of them for the planned axial flux alternator. I'll use two magnets side by side to give a 44mm by 22mm wide magnet pole. As the magnet is narrow, I can fit more magnets and coils around the diameter. Instead of the usual 12 magnets per side / 9 coils layout, I'm using 16(32) magnets per side, 12 coils. More magnets/coils means a higher AC frequency, so more power than a lower magnet/coil count. Plus 4 coils per phase means its easier to wire a stator for 12/24/48 volt operation. While I dont expect anywhere near the power of rare earth magnets, I can see some advantages to using this layout. The magnets are very cheap for their power. 1800gauss for $1.10 in ferrite, the same size magnet in rare earth is 5780 gauss, about 3.2 times stronger, but is worth $22, 20 times the price. Since we are using a weaker magnet, we can use thinner magnet plates, 4 or 5mm instead of 10mm, saving more money and weight. Its also a lot cheaper to get 5mm plate cut than 10mm plate. So by using ferrites we end up with a alternator about 1/4 to 1/3 the power of its rare earth equivalent, for something like 1/10th the price. We also have reduced the weight, and have a alternator that will run cooler and should be more reliable. Plus ferrites dont rust. This is a basic layout, its using the same design as the bigger axial I was building. Diameter is about 260mm. Using two pillow bearings instead of the wheel bearing, the 25mm shaft is fixed. 
When the magnets arrive I'll test them on some 4 and 5mm plate to see how thick I need to go to go, ideally the back of the magnet plate should have almost no magnetic field radiating from it. If a nail dont stick, its OK. Then I'll get the plates cut and go from their. Hopfully I'll finish this one 
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Glenn Nice concept I look forward to the outworking of this one, if I can be of any help let me know. have you done a power out estimation compared to the F&P single and dual rotor? All the best Bob Foolin Around |
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mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Gizmo, I'm also very interested in this new project of you'rs. I'll need to start a search for suppliers for magnets ect. At least I'll have the info available when I'm ready to build something similar. ....Mac46 I'm just a farmer |
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Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Glen, The focus of American and European builders seems to be on larger Kw units.They probably have the wind supply and room to put them up and in many cases aim to be self sufficient,to "stick it to the man".So the impression is to aim for the "rolls royce"of mills.Some Aussie's have the means to do the same.I think there's plenty of room for a smaller,lighter cost effective unit thats suites our conditions.With testing done it will have added benefits simply being siutable to local conditions.I aiso wanted to thank you for the odvious dedication you show as an administrator adding the controller forum,not that i'm up with it but it all helps to be better informed about the possibilities that electronic controls open up to DIY's.My confession is that it would have to be idiot proof to be Practicle to me,but I'm willing to learn.Cheers Rastus see Rastus graduate advise generously |
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| Xmaswiz Regular Member  Joined: 14/04/2011 Location: United StatesPosts: 69 |
very cool, what are your plate diameters you will be working with (rotor & Stator)? Santa Maria, CA. Noel |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Hi Guys No, no power estimate at this time, this build will be the test to see what I can get. I would like to see somewhere around 500 watts or so, that would make it pretty cheap for the watts. The stator diameter is 264mm. It would be easy to scale up. Running 4 magnets in a row will give a 88mm*22mm magnet for $4.40. With the same magnet/coil count would mean a 352mm diameter stator and should mean double the power for the same RPM, so long as the turbine is matched. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Jarbar Senior Member  Joined: 03/02/2008 Location: AustraliaPosts: 224 |
Glenn,I see that a discount for quantity over 100 magnets brings price down to 0.90 cents each so 4*.90 = $3.60. Anthony "Creativity is detirmined by the way you hold your tounge".My Father "Your generation will have to correct the problems made by mine".My Grandfather. |
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shawn Senior Member Joined: 30/03/2010 Location: New ZealandPosts: 210 |
I and many others will watch with interest, and am most interested in price verses power I think many in salt air will head this way after they get sick of rusty neos. I have not stopped my axial build but somtimes life just gets in the way so am very slow 
My new mill will be completly inderpendent to my f&p dual so maby down the track I could upgrade the f&p with one of these I will be wanting more than 500 watts though! Keep up the great work glen I and many others are greatfull  |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
The magnets arrived today. 
Well packed. 
One of the magnets. 
Also in the box was product catalogue leaflet, a fridge magnet and a information sheet that covered some interesting tip's, like how to separate the magnets, what they are made of, etc. Pretty happy with the order, top marks to aussiemagnets. Next I'll so some tests and finalize the layout before getting the steel plates cut. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi Glenn Building a cheaper axial flux is definetly of interest to me, so far on my wind mill has cost me not much more than loose change and it takes me a while to get enough bits and peices togeter to build something, i am shore there are quite a few others out there in my shoes. The size looks about right for when it is time to upgrade from the F/P, it may be a good size for a natural progression as alot of us start out on the F/P. All the best Dean. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
I stuck the magnets on some 3mm plate. In the pic you can see a single 50mm neo N50 magnet and two of the ferrite magnets side by side. 
I wanted to see how much flux was leaking out the back of a 3mm thick steel backing plate, and if I could side two ferrite magnets side by side without them pushing apart from each other. They would sit side by side ok, just. A drop of superglue underneath will help, but I also think a cable tie around the pair would ensure they stay put. I used my gauss meter to take the measurements. The max gauss my meter can read is about 1500, so it was pegged out on the faces of both the ferrite and neo magnets. Reading the back of the plates was interesting. I could detect 23 gauss behind the ferrite magnet, and its a 1800 gauss magnet, so less than 1.3% is lost. What was surprising was the neo magnet, with a reading of 124 gauss. At a guess its a 5500 gauss magnet, so I'm loosing only 2.3%. I'm thinking the 10mm thick plates used on the larger axials might be a bit of overkill. Anyway, I'll use 3mm plate for this prototype. I may gain a fraction of a % in power if I use 4 or 5mm plate, but 3mm plate is much cheaper and easier to cut. I think it will have more than enough strength too. The 23 gauss wasn't even enough to hold a small nail to the back of the plate. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi glenn I think the main problem with 3mm plates will be to get them to run true as they are a bit thin I would be more comfortable wit 5 or ^mm. All the best Bob Foolin Around |
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Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
Gizmo, 
Just Curious whether this would effect Inductance? Looking forward to the Test Phase, it's a good looking Design.  Cheers------Roe Time has proven that I am blind to the Obvious, some of the above may be True? |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Hi Roe Both magnets are facing the same way, not opposite. N to N, S to S, so it becomes a single larger figure 8 shapped magnet. If they were fitted N to S, yeah, it would cancel out across the coils and you'll get no power. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Got a couple of quotes back on the laser cutting, and placed an order with one firm. About $100, including material. Should have them by this weekend. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
HI Glen I"m glad to see you getting back into the creative posture. Sounds like a real deal from here Looking forward to seeing your house light up Bright. ----Cheers, Roe Time has proven that I am blind to the Obvious, some of the above may be True? |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Yeah Roe, its good to get back into the hands on stuff. My stator will be 9mm thick, with a magnet spacing of about 11mm, so today I bought a 600*900mm sheet of 9mm MDF. I'll use this to make the mold and coil winders, plus a jig for positioning the magnets. Will post some pictures tomorrow. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Perry Senior Member Joined: 19/11/2009 Location: Posts: 190 |
Hey Gizmo, Forgive me if I am being daft but it seems like you sized the plate thickness (3mm) based on flux saturation (leakage). Isn't the real reason for thicker plates due to the mechanical loads associated with the opposing magnets? Perry |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Yes Perry your right, but its a small alternator, and the plates will have 1/3 the attraction to eachother compared to using neo magnets. When I scale it up I'll go thicker, but for this little one the 3mm will be strong enough. I've also used 8 spacer threads around the circumference instead of 6, to reduce any bow in the plates between spacers. I'll measure any deflection anyway to check. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
This morning I made the magnet locating jig. Printed out part of the cad drawing at full size and cut into sections, it was too big to fit on one sheet. 
Lightly glued in place and then center punched the holes. In hindsight I didn't need to glue at all, some tape would have worked, just to hold the paper in place while I center punched the holes. 
Finished jig, holes drilled. The magnets are 22mm diameter, and I just happened to have a 22mm wood bit in the tool box. 
Next up are the coil formers. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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