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Forum Index : Windmills : smart drives and neo magnets
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makourain Senior Member  Joined: 19/04/2006 Location: Posts: 111 |
do smart drive motors have neo magnets in them? if no, what kind of magnets do they have and what would happen if i put neo magnets in them? |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
No they dont, they have ceramic magnets. It is possible to convert them to Neo's, and this will almost double the power output. Look here - http://www.thebackshed.com/Windmill/Articles/MattLyons.asp And do a search on the board for neo, should pull up a few results. Hey did you know we have a bunch of better looking icons / avatars? Yours looks a bit spooky. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Matt Lyons visited my place some time back and we stripped a Ceramic rotor and retrofitted some Neo's he bought up with him. He angled them slightly and after they were lined up _they magnetically stick to the steel backing in the rotor,so that's a help- we then mixed polyester resin and poured it into the small spaces between the magnets by making a "dam" with Gaffa tape around the inside of the rotor. They seem to be very powerful on my stators-almost a 2 man job to pull the bloody thing off the stator, but I'm a bit concerned with the cogging ,still too much,I reckon. Bruce  Bushboy |
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| makourain Senior Member Joined: 19/04/2006 Location: Posts: 111 |
why do u space the magnets? why not have one big block of magnet all the way around like a solid ring? surely this would stop cogging? |
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Chris Senior Member Joined: 12/09/2005 Location: AustraliaPosts: 146 |
A solid ring of magnet would not stop cogging. Cogging is when the magnets go past the laminiations on the stator, and they want to "stick" there due to the magnetic attraction. The magnets are spaced to prevent things like magnetic saturation. |
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| makourain Senior Member Joined: 19/04/2006 Location: Posts: 111 |
if magnetic saturation is a problem, why are stronger magnets desirable? [quote]A solid ring of magnet would not stop cogging. Cogging is when the magnets go past the laminiations on the stator, [/quote] can you rephrase? |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Hey Makourain. By "Solid Ring" do you mean one large circular magnet with one pole facing the poles of the stator? If so, then that wont work. Coils in the stator only generate power when the magnet strength through them is changing. So if there was just one big magnet, the magnet strength would stay the same, and therefore not generate any power. Its like if you have a coil and a magnet. If you hold the magnet next to the coil, no power is generated, but if you move the magnet to and from the coil, power is generated. Cogging is actually a good sign, it means there are large changes in the magnet force as the magnets pass over the stator poles. But cogging also means the windmill is hard to start, so you need to find a ballance. Too much cogging, where the windmill would make more power but is harder to get started, or less cogging, where the windmill makes less power but starts easily. I like your new avantar, looks cool. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 573 |
Hi Makourain l like your icon as it look great About solid magnet ring as you can find reject large wireless speaker as have simlar ring magnet and carefull when you pull apart and dont break it as they are glue on to metal frames so give ago . dwyer the bushman |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Glenn, just pondering here. There is probably a good reason why it won't work (or won't work efficiently), but here goes. How would it be if a machine was made with the coils all quite flat (ie, low profile) but AIR-CORED, so the entire stator is just copper (ie, non-magnetic). Magnets on either side (either top/bottom, or inside/outside) mounted such that alternate pairs present n/s then s/n orientation across each coil. There would be no cogging because there's nothing the magnet would be attracted to (well, until there was a decent load to induce fields back in the windings), eddy currents would be eliminated, weight would be reduced. Has anone done any research on this perchance? As an alternative (subsequent) thought, how would it be to make the core out of ferrite or other (possibly ceramic) material. If it doesn't conduct electricity, eddy currents would be eliminated while maintaining the magnetic properties. (wouldn't address cogging though) |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Hugh's ( http://www.scoraigwind.com/ ) early brake drum windmills worked this way. It does work, but like you say, the efficiency is not as great as a laminated pole / magnet configuration. The pancake designs seen on http://www.otherpower.com take this a step further with their coils embedded in an epoxy disc, with magents rotating on each side. It has no cogging, but there are other problems. As its not an efficient design, they need to use large expensive magents, and there are issues with coils overheating as they are completely covered in glue with no air ventilation to speak of. remember magnet fields dont like traveling through the air, and no commercial design that I know of uses air cored coils. The old F&P motor may have cogging problems, but for their size and price, make a bucket load of power. A F&P can be picked up for about $30 ( or free ), and they make over 300 watts easily. We just need sort out a few little problems. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
I have had a go at explaining the magnetic field/pole behaviour on the Alternative Rotors page. I'll try harder this time. I wish I could draw a picture! Consider a pair of magnetic poles, one North one South with their opposite ends stuck on to a piece of magnetic material, steel say or iron. The magnetic field has no trouble passing through the magnetic material, but plenty passing through air. Air is several million times more difficult that iron for a field to exist in. From the ends of the magnet away from the iron, the magnetic field will exist in the space beteen the two poles. It extends out into the air a bit, then across to the other pole. Because its out there, a little away from the magnets, we can get at it and make use of it. If we move the two poles immediately together, because of this difficulty with air, all the field will exist only in the magnets and none in the air. So we can't use the field from the two magnets. We have to come to a compromise of moving them just far enough apart to cause enough field to exist in the air. Then we can bring another piece of magnetic material close to both poles and the magnetic field will change from existing in the air to existing in the magnetic material. If there are coils of wire on the magnetic material that we bring close to the magnetic poles and we then move them past the magnets, a voltage is induced in the coils and a current can flow. Now, there's another compromise in how close we can get between the magnets and the magnetic material carrying the coils. The closer we get, the less the air gap can reduce the magnetic field, so the stronger magnetic field allows a higher voltage to be produced - but the greater the force of attraction, so maybe we can't even move the coils, so no voltage is produced. In classical generators, there are not always many poles, ie magnets. A two pole machine will have only two of course and if the machine is say 200 mm in diameter, the centres of the poles will be 100 apart. That would be far too much air for any useful magnetic field to exist in. So the rotor, made of excellent quality magnetic material is made to be a very close fit between the two poles. The two air gaps together may only be 0.5 mm. As there is virtually no "drop" on magnetic field strength through the magnetic material, almost all of the magnetic field that it is possible to creat exists in the air gap between the stator and the rotor. And that's what we want. As much of the magnetic field as we can get, between the two working magnetic components. And yes, this causes cogging that we don't like too much, because it makes mills hard to kick off and easier to stop. Personally, I'd love to see the difference between two otherwise identical F&P units in identical winds, one decogged and the other "au naturel", so far as energy delivered is concerned. Decogging will slightly reduce magnetic interaction, meaning slightly lower voltages, but more actual running. Whether or not its effective running, I do not know. Megawatt Man |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Now here I go, about to show my ignorance, maybe, I dont really know. I believe the F+P machines would have even worse cogging problems if they were not wound three phase. Every 'clunk' of that cogging is 14 poles moving to be attracted by their respective magnets, the other 28 poles being at some other point in the cycle. Imagine what cogging would be like if all 42 poles were moving in phase? So... hows about splitting those three winding into say six phases then when adding the neo magnets position them to suit? |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5019 |
Yeah your right. If you reconnected the stator as a 6 phase machine, and then, I think, used 49 magnets, it would work and you would have less cogging. But.... In its current configuration, for every 6 poles there will be 2 aligned with magnets at a time. If you reconnected it for 6 phase, you would only have 1 pole per 6 aligned at any one time, so you would have half the output voltage. I think 
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Not sure Glenn, I am thinking that total power is the number of poles going through magnetic transition per second? Less magnets might mean a slight increase in RPM to catch up but thats only the ratio of magnets-now to magnets-before the modification. You would definitely have less volts, thats for sure but amperage flowing in each phase would be the same, so twice as many phases at half the volts and watts stay the same. Like you said "I think" |
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| Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
A bit more on the explanation of magnetic circuit and motor theory. I stuffed up a bit telling people that in a 200 mm diameter machine, the pole spacing would be 100mm. Idiot. Its closer to 200mm, depending on thicknesses etc. About cogging. There would be the same cogging effect even if there were no coils on the stator. The cogging is caused by the magnetic attraction between the the magnets and the radiating stator coil mounts. I have asked F&P engineers about the different numbers of magnets and coils but they don't really want to talk about it all that much for understandable commercial reasons. I think it most likely however that if they had the same number of coils and poles the cogging would be far more obvious and noise would be a more serious problem. I reckon they have been and probably still are experimenting with various arrangements and have found the 56/42 combination the best compromise to date. Megawatt Man |
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