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Forum Index : Windmills : The Plodding VAWT
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Greenbelt Guru  Joined: 11/01/2009 Location: United StatesPosts: 566 |
Efficiency goes to Pot when you gear drive your Vawt. 
I have had this on my mind for some time. so Have a look at this and see why There could be great advantage by incorporating this into the finished project. A direct Drive alternator in a VAWT Can be almost any Design you can dream up because size does not interfere with the Blades. Weight is a factor But spider weight framework can be strong. Neo Mag's and air core coils at Greater Radius will reduce the Cut in rpm. 
This is what Bob did to his blades to get a little more Torque. You can see that a little more hub size would not disturb this Design.
Time has proven that I am blind to the Obvious, some of the above may be True? |
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mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Greenbelt, Thanks for posting this "large" concept alterntor. Its what I've had rooling around in my mind for a few years now, ever since VAY4AQ mentioned it in passing in one of his posts. Its morning here...my meds. have'nt kicked in yet, coffee is'nt made yet, so I'm in dire straights for the moment. Lots of close lightning strikes in last nights storm so little sleep. I'll post again later. ...Mac46 I'm just a farmer |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
That's Why I geared my VAWT 6.4:1  .
I require an alternator that fits inside the square lattice mast so its size handicapped. But I do like the challenge to build a better one that the unit used at the moment. Klaus |
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| Xmaswiz Regular Member  Joined: 14/04/2011 Location: United StatesPosts: 69 |
from what I am reading , we would still use the same number of mags and coils? this would also allow you to add some windings because of slightly more room, and cross over by the mag would still be effectively the same? at rotor 1 size you could comfortably have room for 24 mag to 18 coil count. since it is an air gap basis, would there be any benefit to have steel just around the circumference of each mag separately (creating a ring around each mag at same thickness as the mag), and use dual stator design instead of a steel plate for the rotor(s)? Santa Maria, CA. Noel |
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| mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Greenbelt, Again, thank you for posting this. What I had I mind is simular in size, but with stationary coils around the circumferance, porcilan, or even big old plain magnets on the rotor. I have'nt experimented with this idea at all. (Something in the three foot dia. size range). I need to my mill going and tested before I can proceed with it. ...Mac46 I'm just a farmer |
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
Hi Guys, Thanks for the interest shown, Work in progress should not be altered to mess around with this. Those who have not yet begun to build should consider this option. It does not have to be a monster to build a 18-24"inch(46-61cm)Rotor/Coil Alt. A 1.5m. (5ft.) dia. VAWT. Would be a good size to learn about whats needed to make a real Producer. Keep the Mags small and weak, close together and lots of stator coils with minimum wire turns and series connected. Posted in January 2010, Overdrive VAWT This Link is an earlier post on this Idea. After reading it again I see confusion in the Comparative Section. For this to make sense, Numbers must be placed for a F&P HAWT to get the picture of how much quicker this large rotor cuts the Mag field in the same wind. A lot of you Fella's have more experience around magnets and Coils than I, So the question on steel rings and plates could best be answered by Others. ------Cheers, Roe Time has proven that I am blind to the Obvious, some of the above may be True? |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Assuming you are talking about a disk type magnet and its magnetized so that the N&S poles are on the circular surface - on opposite sides. Now, think about what you asked. Imagine the magnet is suspended in free air somehow and the magnetic force lines are visible. You would see them coming out of the N pole face and wrap around the edges to get the shortest distance back to the S pole face. About the middle of the magnet pole surface the lines have to travel further and their concentration is less. What you want in an alternator is to have as many magnetic force lines as possible travel *away* from the pole surface, straight through the coil and to a iron path (or another magnet as well) on its other side, from there to a similar set up to the iron backing of the first magnet to complete the path of the magnetic force lines. What you suggest would seriously short out the magnetic lines *before* they have a chance to travel through the coil and do their work. You might want to draw that out so you can see what I mean - I'm no good at doing fancy drawings on the computer, Klaus |
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| Xmaswiz Regular Member Joined: 14/04/2011 Location: United StatesPosts: 69 |
example with ring around circumfrence (red ring ) field line pulled in against the side of the magnet, but stil free space up and down, this is a question about how the lines would react with just a ring. The idea is still for airgap but dual stators one below and one above the rotor. excuse the bad drwaing. 
hope this makes sense at all, sorta like a cup magnet but no cup just the edge of the cup? Santa Maria, CA. Noel |
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
XMASWIZ HI, Thanks for the Input, all questions help us learn and Basically that's what we do here. I would suspect that TINKER is correct about the shorted Field. The steel plates used to mount mag's is normally supposed to link the fields on the back side to prevent flux leakage (expanded field) This apparently helps to concentrate the intensity of the field at the working pole face.???. The drawing below is my take on the flux field. Tinker, Thanks for the Info. ----Cheers, Roe 
Time has proven that I am blind to the Obvious, some of the above may be True? |
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| mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Greenbelt. I'm at a loss for proper ediquett so for give me if I step on toes... I will be starting on building the alternator for my mill in the upcomeing weeks. I have no background with these air cooled "Aux flux" alternators...and intend to spend some time reading about them. I had orginally thought of a different style alternator, and will probably be testing both concepts, as well as you'r new concept that you posted here. I was just wondering if anyone had tried an alternator that uses electro magnets to induce the coils? Changeing the power to the magnets would control the power output. ...Mac46 I'm just a farmer |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Mac46, what you suggest is just how a car alternator works. It works very well in a car as it runs at high RPM. For a windmill you would have to rewind the stator form a few turns of heavy wire to many turns of thinner wire. Doing that would make it useful at lower speeds but you trade off the high Amp output of the original version. Basically simple is best, a rotor with permanent magnets requires no electric power input, no slip rings & brushes and external power source provide it. But, by all means do some experimenting with that idea, just remember to deduct the power at the field from the output to get a net power generation figure. Klaus |
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| mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Tinker, Thanks for posting,... I almost did'nt ask that question, because I knew of the lower efficiency inherint in the alternator design, plus the slip ring issues. Thanks for pointing these out and I understand that the maximum amount of power produced with the least amount of design change is paramount. This helps me understand things alittle better. Power can be managed with a dump load...much less complicated. I have a tendency to over complicate things. Green belt, Sorry for hijacking you'r thread...though I thought it was sorta related to a new concept alternator subject. The speed of the magnets induceing current in the coils is something I realized and was thinking along the same lines as what you have posted in the vawt design alternator. Like you stated,...very little cogging, easy start up, max power at lower rpm. Ideal application for a vawt. Thank you for posting this concept. ...Mac46 I'm just a farmer |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew I'm tossing this in just to keep everyone's thinking on par with what works and what doesn't: Oztules, a retired 4m member, emailed me back in the day with something that turned my thinking around and cleared up a lot of errors as far as designing alternators. His jewel of information was this: Magnet flux paths should be treated as electric circuits. By treating the magnetic field as a circuit, it has to have a beginning as well as an end. The magnetic "circuit" must be complete in order for there to be any meaningful current generation. What this boils down to as far as generating an electric current is there has to be a complete circuit in the coils as well as in the flux path. The wire size determines the current (Ohm's Law) and the rest is left up to flux density, air gap (sweet spot) and rotor speed. That's about all there is to it. So, designing an alternator that capitalizes on all 4 aspects will render the best outcome. To complete the flux circuit, there needs to be a flux-return pathway established. In the axial-flux rendition, that pathway consists of an iron backing plate connecting alternating N and S magnet faces. The open faces of each magnet seeks its flux-path return through an air gap and then to its opposing-face partner on the other rotor. Occupying this air gap is the coil array. In an air core, there are only magnets on one side of the coil and the coils must be wound on iron cores or the entire coil array must be "potted" in resin containing iron filings or magnetite. This approach is less effecient, but easier (usually) to construct. In either case, a magnetic field that has no defined return pathway will produce little or no meaningful voltage or current. That's just the way it is. Hope this helps someone. I wish I'd know about it prior to my initial (several!) builds. . . . . . MC Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
MacGyver, Thanks for posting this info, I almost new this...not. Probably saved me from pulling my hair out. I have been reading and studying...some. Starting to get in to it with more and more understanding. ...Mac46 I'm just a farmer |
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| Air Bender Senior Member  Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi Greenbelt While i think your concept of a large diameter alternator is good, i can see potentual problems with the build. Having never built an axial flux i have no idea how hard it is to build with enough accuracy and strenth to maintain a close air gap but i can inmagine it would become more difficult the larger the diameter becomes. If this an issue it may better to build a big diameter f/p type alternator. All the best Dean. |
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
Air Bender The Best I've seen in design and strength On page 5 of this post it is obvious that this is one strong frame. Though Glen chose a magnet plate Diameter of almost a foot,(11.85inches,300mm.)it could easily be made several more inches Wider. For such a Build I would make a 8-10 sided plate with the necessary extra Bolts an add a stiffener ring to the rear magnet plate at the center cut out. EDIT; The stator may need to be Stainless or Alloy aluminum to help reduce flexing on this larger Diameter. As Glen proved the Neo's can move the electrons, His 10 turn coil can produce 2.28 volts.at 133 rpm. This is 1 volt to 4.4 turns of wire, 62 turns = 14 volts. 5 coils in series for a grid tie at 70 volts, 133 rpm. Glen would need 75 turns with 4 in series for 68 volts. "pretty Nice!" --------Cheers, Roe Time has proven that I am blind to the Obvious, some of the above may be True? |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Hi Mac. Your posts usually make lots of sense but the above bit about "air cores" does not. You can either have nothing magnetically conducting (air) inside a coil core or you can have it wound over an iron core. But you cannot have both at the same time
Air cores pro's: no cogging no saturation of air core. Con's: requires much stronger magnetic field. Iron cores pro's: air gap is kept at a minimum, weaker magnets might suffice. Con's: severe cogging unless counter measures are taken. Iron can saturate if the magnetic field is too strong. Keep in mind that iron conducts magnetic flux about 10,000 times better than air. Even a small air gap makes a *big* difference - every fraction of a millimeter counts. So, now on to air core magnet arrangement: You can have a single rotating iron disk with the magnets on it and the stator coils epoxied to a stationary iron disk on one side of the magnet, but NO iron within the coil itself. Thus no cogging as the distance the magnetic flux has to travel is the same all around the disk. You can have the stator coils on just an epoxy substrate and rotating iron disks with magnets on both sides - gives a much stronger magnetic field for the same air core. For identical magnets and distances this arrangement effectively doubles the flux concentration of the example above. Klaus |
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niall1 Senior Member Joined: 20/11/2008 Location: IrelandPosts: 331 |
interesting discussion... one thing i,m wondering about is having any kind of static metallic plate behind or incorporated in the stator ....would,nt this give rise to strong eddy currents which would have a braking effect ? i think in a dual rotor axial if you remove one rotor and run it up ...it,ll work... (up to a degree)...but you,ll have lost half the magnet strength ...and the "flux circuit" will be a bit iffey ...some small axials seem setup to work like that just thinking too much ...
a fun test with eddy current is dropping a small neo through about i meter of copper pipe ..it messes with you head a bit niall |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
tinker I based those comments on a small mill I'm currently bulding. What I've done is potted a skein-wound coil in resin mixed with magnetite. This surrounds the coil(s) with a magnetic substance. The magnets in this case are half an axial-flux wheel. That means the magnets are arranged alternately N and S on the wheel, with a backing plate tying all their back sides. Their front sides must "bridge" to one another. By running this up close to the magnetite-infused stator, those lines of flux have a better return path to each other and thus will produce more electricity than if they were to jump the air gap on their own. I think the confusion here is that I've "assumed" (and you know what they say about that!) that since I have removed the opposing axial-flux wheel, I'm now running it against air. That perhaps is a mistaken description and is likely where the confusion sets in; sorry. What I'm building here is more like an F&P than a true air core, so just to set the record straight, if I were to run the magnets against the coil with NO magnetite mixed into the resin holding the coil(s) in place, THAT would be a true air core. I actually have a pretty good grasp on this (thanks to Oz) but I have failed in my communication efforts. I'll try harder next time. 
. . . . . Mac ps This mill will cog. If I get reasonable output, I'll redesign it to have the magnets offset and use more of them than coils to reduce the cogging effect. Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Greenbelt Guru Joined: 11/01/2009 Location: United StatesPosts: 566 |
naill 1 You know , I'm aware of eddy currents in magnetic Iron/Steel and always accepted it as a part of doing business. The silicon steel laminates kept the system fairly efficient and was not a problem So I am not as sharp on the non magnetic metals, I assumed it would be a small amount and not a great concern. Thanks for calling me on it. This could save someone some money and lots of time. You're Right, an education for Dummies like Me 
I have a Fix though, 
-------Cheers, Roe Time has proven that I am blind to the Obvious, some of the above may be True? |
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