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Forum Index : Windmills : The Latest from ART Turbine
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| electrondady1 Senior Member  Joined: 12/02/2009 Location: CanadaPosts: 208 |
the very thing that makes your mill so attractive is what is reducing it's power output. the wide base wants to rotate at a different linear velocity than the narrow top. one end is dragging the other end around. the other end is acting like a brake. one thing i noticed over the last ten years, when it comes to verticals, very few build them to personally make use of whatever power they produce. but so many want to immediately go into manufacturing in a big way. or even better, patent and licence the manufacturing. it becomes an exercise in investor hunting or sales promotion. they want to sell the world on their widget before it's really working. |
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| Drewartturbine Newbie  Joined: 09/08/2011 Location: Posts: 30 |
Thanks for the comment electrondady1. I disagree that they bottom is dragging the top, though it's a reasonable idea and I can understand how you'd get there. The reality is in the numbers, which you can see in the report if you wish (link posted above). What's actually happening is that some flow into the turbine is moving upward, increasing the velocity of the flow that's above it, and effectively locally producing a higher velocity, and therefor maintaining a fairly consistent TSR. I agree, selling the widget before it's working is fairly common. I would also say that an issue in wind turbine design by the DIY movement is that people often too early try to slave an alternator of unknown efficiency, that they don't know how to, or have the tools to properly measure. R&D is best done one step at a time. When trying to reinvent the wind turbine, first get the turbine right, then put an alternator on it. |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi Drew I think you have developed a great looking turbine. but the main issue with a VAWT is the alternator, lots of people are building VAWT turbines, but as far as I know, no one has invented an alternator that will produce a decent amount of power at the low rpm they run at. If this can be done by gearing or alternator design I will go back to building VAWTs. For me getting the alternator right is more important than getting the turbine right. All the best Dean. |
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| Drewartturbine Newbie Joined: 09/08/2011 Location: Posts: 30 |
Hi Dean, I'd love for community members to check my thinking on Alt design which goes as follows- Given that their is a lower operating rpm due to lower TSR (1.2 to 1.5 for ART) Then a suitable alt for a low RPM turbine will need more magnetic poles in a larger dia circle, as the larger the circle of the magnet array, the more poles, and the more magnetic flux you can get, the faster the poles will move over the coils ( 12" dia circle will have roughly a 37.2" dia ring, so would be 40" per rev speed, whereas a 24" dia ring would have a 76.4" ring, so 76.4" per rev. So, the larger ring alt gets the benefit of both 2x the speed, and 2x as many magnets (more flux)? If the coils are the same size, but 2x as many coils, the total output should be 4x, in 12" vs 24"? An issue with how the coils are connected could be that if you connect all the coils in series, you increase the resistance? |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi Drew If you double the size of your alternator, you will also need to double the size of your turbine. The problem here is when you increase the diameter of the turbine you also decrease the RPM of the turbine which puts us back to were we started. The only way around this that I can see, is if you increase the diameter of the alternator you decrease the strength of your magnets. I have a feeling that if you double the diameter of the alternator you may have the decrease the strength of the magnets by more than half. All the best Dean. |
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| electrondady1 Senior Member Joined: 12/02/2009 Location: CanadaPosts: 208 |
maximunm crossing speed is at the outer edge of the base. maximum room for mags and stator coils. consider a dual rotor radial design. |
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| Drewartturbine Newbie Joined: 09/08/2011 Location: Posts: 30 |
Thanks electrondady1, The configuration right now is 2 1.35 meter dia annular metal plates (held apart by 12 x 1/2 jacking bolts, I do have up to 2m dia available, but it's much easier to work with what I have. What I did was buy 144, 1" x 1"x 4" ceramic magnets, and glued them to the plates, so each plate has 72 poles. I hoped that that volume and number of ceramic magnets would be enough to generate the output I am looking for. What I found was with a test coil, that I'm only generating 1w where I need to be generating 10 w to sufficiently load the turbine. So what I'm thinking is I switch to rare earth magnets, using 3 of 1"x1"x1/2" thick magnets (to make a strip 3" long). The ceramic magnets have a latching force of about 16lbs. The Ceramics have 64lbs each or 180lbs per strip. This should give me 10X the flux, in 3/4 of the space? Also because the strip isn't quite as long, I shouldn't have to have them quite as close together on the inside circumference, and so might have more focused flux? I also have gone away from using an interleaved coil design, just using standard coils now (set of 54 to go with the 72 poles). If I needed to get a bit more juice, in theory I've could go back to interleaving coils, and increase the amount of copper in the stator by 1/3 (should increase watts out by 1/3?) Does that sound reasonable? I am a bit worried about the pulling force between the plates. 12x 1/2 bolts is pretty strong, however if the magnet plates were ever to come together, I'd have somewhere around 23,040lbs of force holding the plates together. |
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| electrondady1 Senior Member Joined: 12/02/2009 Location: CanadaPosts: 208 |
i studied product design back in school. the thing they hammer into you and what you find out in industry, cost is every thing. direct drive is a beautiful thing. but a 2m. dia. alternator could power a village if you turn it fast enough. better i think to build a 10 inch alt and overdrive it with a $10.00 belt better sill, eliminate the belt and run an alt. directly off the rim of the base. |
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Greenbelt Guru  Joined: 11/01/2009 Location: United StatesPosts: 566 |
Hi Drew; I agree with your Thinking, speed is necessary for successfully generating electrical energy. A VAWT being a slow speed machine will require some ingenuity to reap its benefits. some years ago NASA built a VAWT (Many VAWT's) Their Best designs were tall with very small base and twisted Vanes. Some two years ago I posted the Idea of a large diameter rotor for a VAWT turbine but I can not locate it. It could be in a thread by " Mac46 " when he built a beautiful VAWT . You Have stated a 20 cycle speed for your test Data, assuming a 1 inch magnet an 2 one inch coils at a radius of 26 inches,(.66M), will occupy 7 degrees of the rim. This will be 3 inches on a 163 inch circle. At 20 rpm = 1/3 circle per/sec.= 120 Deg. when divided by 7 deg.= 17, this would give a frequency of 17 hertz for this coil set when magnets are spaced at 3 inches. I would suggest at this low frequency you use Iron core coils to get the voltage up  The purist's out there will frown at this but air core coils need quick jolts to make the watts. Keep at it, perseverance will make you Proud
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: 5078 |
Just gear it up. Gear drives are the most efficient, followed by chain and toothed belt. Its often commented the use of gears/chains/etc rob power and should be avoided, but this is really not the case. A gear drive is around 96-99% efficient, but difficult to make/use for the average backyard workshop. Chain drives are over 95% efficient, and relatively easy to use, but must be maintained to keep the efficiency up. However remember, you should try to use sensible ratio's, like up to 1:6, and avoid multible sets. Also chains dont like laying on their side, so for a VAWT you may need to keep the chain length short or use chain guides, or go for gears. People like Chris Olson are using geared up alternators with very good results, for less cost than a equivalent power direct drive alternator. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Back when I was racing Karts we used toothed belts rather chains as there was less power loss. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Depends on the oil. Chains with light oil are up over 98% efficient, but need more maintenance. The loss in a chain comes from friction in the bending of the chain, and load on the bearings if the chain is too tight. Like gears, there should be no wiping of surfaces in a correctly set up drive. With belts its the bending resistance of the belt, and again bearings if the belt is too tight. Belts can be difficult to use though, its easier to add/remove links in a chain, and chain sprockets are easier to come by. But belts are virtually maintenance free and quiet. 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 |
I built VAWTs for years, If I was to build another it would be geared to run a small alternator fast, if it burns out than go for a bigger one. If you add an alternator that is to big the turbine will not be able to push it past cut in (the speed were the alt starts to load up], If your turbine cant push the alternator past cut in you will never get more than a trickle charge out of it. From my own experience you will make more power running a small alt fast than running a big alt slow. All the best Dean |
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| Drewartturbine Newbie Joined: 09/08/2011 Location: Posts: 30 |
Thanks Dean, Glen, Madness, electrondaddy1 and Roe, for your input. I agree that stepping up speed via belt/chain or rim drive is a potential path, and it is a direction I will purse next, if I can't get this worked out. I also agree that keeping cost down is a very important factor. I'm going to keep at the direct drive PMA for a bit longer though, as I don't feel I've yet proved that it'll be impossible, or too expensive. I do agree that it's likely a similar output system using as speed step up system and a higher speed PMA might be less expensive. I'm aiming for extreme simplicity. At this point my existing array is 144 ceramic mags, costing .60, so just under $100 worth of magnets, weighting almost 150lbs. If I switch to rare earth magnets, my magnet cost will be closer to 350.00. A big increase in cost, but in the grand scheme of things, at trying to keep cost under 3,000/kW, not too bad. One thing that's a fundamental part of my design is to use a PWM controller, (Midnight Solar), and clipper speed control system. This allows a programable power curve, which effectively turns on and off the alternator at different rates for different speeds, so that I can build my alternator to max power output at 40km/hr, but have that alternator not overload and bog down the turbine at low wind speeds. Thanks all! |
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mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
You are correct in that the wind moves vertical inside of the spinning rotor, more so when it begins to reach speed. I like the shape, but controlling a balanced rotor under load and at speed has been my big problem, not to mention not a big enough break to stop the thing. Life has kept me way to busy to be able to get back to my project, but I am very interested in this (you'r project). Greenbelt is right about the larger dia. alternator instead of gearing the rotor up...its getting the right size and shape wings and a support structure to hold everything solid thats most important, but the large diameter alternator is the real secret here. Find you'r average wind speed range and build a alternator slightly smaller than what the math says...and it should work. It needs alittle room to be able to reach its power band and come up to speed. Gret mill...keep working at it...yep, I like it, has lots of potiential. Mac46 I'm just a farmer |
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
Hi Dean, I'm in agreement to most of your post with one exception. 
The Way an alternator is built determines the power requirement, its physical size does not have to be a prime mover just because it looks like one. I see a large radius rotor with lots of low flux magnets with just a few induction coil pairs spaced at 15, 27.5, and 40 deg. sequence separation. Adding coils a few at a time will allow controlled loading rather than building a monster and having to junk it and start over. I would Begin with six test coils for 3 phase. Dividing the rotor rim (360 deg x 15 deg. = 24), There are 24 places where a coil set could be located, Mark them each as (15), Beginning at the first 15 deg. marker, Divide 360 again by 27.5 = 13 places for a coil set and so on. Pick a 15 Deg Mark and measure a coil width in degrees both forward and backward of the mark and situate the coils so that the mark sits between them. then do the other 4, at 27.5 and 40 degrees measured from the center line of the first coil set. With many magnets passing the coils on each turn the rectified frequency would be triple the single coil frequency. Several test coils will have to be made to determine the final recipe. The spacing of the Coils should not cause a balance problem because they are not rotating, there could be a light force factor to one side of the rotor but it will always be in the same direction due to the magnetic reaction of the passing magnets There are many ways to skin a cat and this is not a plan to immortalize, it is I believe the way I would approach This project. When a person posts a project of "his interest" and is seeking advise it is my opinion that he is not interested in doing what everyone else is doing, he wants help and ideas that will further develop "his project" I believe he is willing to face failure after exhausting all alternatives. As MacGyver says the fun is in the trying, Aanother Famous person says "Sometimes it just works" 
Cheers----------Roe PS Glen; The Italics button does not do anything. Cheers--- Roe Time has proven that I am blind to the Obvious, some of the above may be True? |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi Greenbelt I agree with you approach to building a large radius alternator and it is certainly worth trying. I think that gearing should be avoided were possible and having a direct drive alt is the best solution. Building the right alternator for a VAWT is the biggest hurdle. I am not saying gearing is the best way to go, but it is just the way I would do it. I would truly love to see someone build good large radius alt. All the best Dean. |
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| Drewartturbine Newbie Joined: 09/08/2011 Location: Posts: 30 |
I'm taking the turbine into Victoria (B.C. Canada) to show at a conference on sustainability. Thought you guys might get a kick out of seeing it ready to ship. I'm sure it'll gets some interested looks on the highway! You also can see the Alt, yellow ring is the lower magnet array, gray inner ring is the mounting plate for the coils. Soon I'll be removing it all, to install a proper lower bearing. Was a botch up in the way it's put together, right now the bearing arrangement is a bit ugly. When I have it apart I'll be changing the magnets from the 1x1x4 ceramic to 1/2x 1/2x 3" rare earth. This will also allow the winding to be a bit shorter. 
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
Hi Drew; I must say, That is a great looking piece of art. I have another suggestion for you about the choice of magnets. Several articles I have read in the past point out the desire to have the magnets wide enough to cover the coil face and also to almost bridge the gap between coil pairs or overlap slightly. Attention to this detail will improve the wave form. 1/2 mags. don't give much room for coil winding. 
Its Looking Good. -------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: 5078 |
How much power do you expect to make from that machine? Just looking at the size of it, the area facing the wind isn't that big. Since we can work out how much energy can be extracted from a cross section of the wind, its pretty easy to work out how much power a windmill, be it vertical or horizontal, can be expected to make. If you know the height and width of your turbine, work out its area, probably using area of a triangle maths. I'm guessing 2 to 3 square meters facing the wind. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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