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Forum Index : Windmills : Coil winding
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imsmooth![]() Senior Member ![]() Joined: 07/02/2008 Location: United StatesPosts: 214 |
I see coils wound with a large empty space in the center. The wound wires form a ring. If I'm using an axial flux design, so there is no iron core, is there any problems with starting the winding much closer to the center of coil? Instead of having an inner radius of 1.5" and an outer of 2", can I have an inner radius of 0.5" with the same outer diameter? This would get me more turns for each coil. |
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GWatPE Senior Member ![]() Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
All these aspects with coils have been thought of and tested before. Any part of the same coil that cuts the same magnet where a wire is entering and the same wire is exiting the field will cancel the induced emf. Ideal is for all the wire length that cuts through the field to be perpendicular to the field, and the biggest magnetic field. This is the idea with wave winding, and a similar approach I used in my 4phase stator, with overlapping coils, so there was minimal air space in the magnet air gap.[nearly all copper coils] There is a problem with this in that the wire that links the ends of the active wire parts still has resistance, and this degrades any benefits. I am sticking to round magnets and round coils now and large rotor separation airgaps. In my new design the coils will end up around 12mm thick with an inner dia of 42mm and an outer dia of approx 66mm, for a 50mm magnet dia. There is no exact science here. I have made a test rig with the same physical magnet rotor dimensions as the alterenator. You will probably need to do the same, to test the coils you intend to wind, for the system voltage. There is a fair bit of experimentation to get the best compromise. You have a fair way to go to yet. Gordon. become more energy aware |
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imsmooth![]() Senior Member ![]() Joined: 07/02/2008 Location: United StatesPosts: 214 |
"You have a fair way to go to yet. " Tell me about it... ![]() |
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oztules![]() Guru ![]() Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Smooth, Try and keep the inner at least 3/4 of the size of the magnet width. Much less will start to be self defeating. The ideal is the same with as the magnet, but in a real world setting where resistance is a reality, it pays to wind inside the magnet width a bit. The emf you lose by cancellation inside the width is made up for by the less resistance per turn due to the smaller perimeter. (less inches per turn). It starts to be too much compromise when the inner is less than about 3/4 magnet width.... this may vary with magnet geometry though, so test coils are the key. You can try different coil shapes and inner dimensions to see what suits your magnet shape and airgap. I think there is some flux line focusing involved when the gap is tight, and may allow for smaller holes. As the gap increases this benefit may become less. (just supposition on my part though). The graph I presented of Dinges above will give you some more clues as to what gaps to aim for for the best EMF for the least resistance. Too close a gap means small winding space in a higher flux region. To wide a gap means plenty of winding space for thicker more in hand wire, but it will be a game of diminishing returns at some point. Normally, 1/2-43/4 of your magnets depth is ballpark ok. (twice the thickness of 1 magnet is your depth). The coils Gordon is talking about will give a very low resistance winding (and he may even need external resistance if he does not use series caps ![]() To this end, use the best magnets you can afford, the resistance is always better outside the stator than in... and the braking will be very solid. Just my opinion, but I don't think you need 10" of root. 8" is fine, as startup is not an issue .... at all. The blades are not very big, so 8x2 lumber is more than sufficient..... but the 10" looks cool. ![]() ...........oztules Village idiot...or... just another hack out of his depth |
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GWatPE Senior Member ![]() Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi oztules, & imsmooth, I am looking for high alternator efficiency, combined with a low cutin rpm, without any electronic switching or DC-DC converters. I am not planning on using any added external resistance, but only the variable impedance offered with capacitance in the voltage doubler/trippler/whatever is needed. The very low winding resistance coupled with the normal rectifiers to the battery will tame the upper power levels, by offering controlled stall limiting loading of the blades, in a way that combines to supplement the furling. The effectiveness of all this will need to be confirmed with proof in the pudding testing. The rotor will be approx 2.8m dia initially. This will possibly be increased to 3.2m dia, with the modified Lacota type blades. I have posted some pics, but they are much better when viewed first hand. I ask again, What happened to the F&P mill with the custom Neo magnet rotor? Gordon. become more energy aware |
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imsmooth![]() Senior Member ![]() Joined: 07/02/2008 Location: United StatesPosts: 214 |
Oztules, I have already laminated and done the jigsaw cut on the lumber. If you want to keep an eye on the progress bookmark bladecarviing. You can follow the progress as I develop a nice webpage for others to follow. I also got the 2" x 1/2" N48 magnets in the mail. I had to use a plexiglass lever to begin to pry them off. They each have about 104lbs of force. I will be wearing gloves when I take them apart. I don't need to lose fingers or have flying projectiles in my basement. ![]() |
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DaViD![]() Senior Member ![]() Joined: 14/01/2009 Location: United StatesPosts: 120 |
Uh,I like all of my 11 fingers ![]() If your not living on the edge your taking up to much space! |
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oztules![]() Guru ![]() Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Nice pages Imsmooth. I will follow with interest. Those magnets sober you up pretty quickly. ![]() .........oztules Village idiot...or... just another hack out of his depth |
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Tinker![]() Guru ![]() Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
part quote: Hi Gordon, Your mention of 'wave winding' caught my attention it's something I know nothing of but would like to rectify ![]() I did a google search on the subject but unless I wade through the thousands of hits all that was mentioned related to communtator type armature winding. Would you know of a site where a picture shows wave winding relevant to axial flux stators? You know, a picture speaks a thousand words and I would like to picture just how the stator windings are arranged with 'wave winding'. Thanks, Klaus Klaus |
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GWatPE Senior Member ![]() Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I remember some pics on this site. Can't remember exactly where though. I would not go with it again, as the return on effort is very low. Gordon. become more energy aware |
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