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Forum Index : Windmills : mags and coils,
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| bigislanddave Newbie  Joined: 26/11/2011 Location: United StatesPosts: 4 |
Aloha every one. This is my first time here.My name is David. My question is, how many coils and how many mags, i will explain. I am living of grid on Mauna loa about 3500 feet up. I dont get alot of sun but i do get wind from all directions and it can be turbulant. It would be nice to generate enough wind power to run a small fridge and tv, at present i run a small 1200 watt gas generator and charge two car batteries and have lights etc. I am about to start my power system and i would like to make sure the vawt. that i am about to build is done with a lot of input from those who have experience building vawts. I may have jumped the gun a little by buying #18 mag wire all ready. I do not intend to buy neo. mags i will be using microwave mags. I am very strong in the mechanics end of things and have most if not all of the tools it will require for the fab. My problem is finding the info that will determine the spacing of mags and coils.I have looked on the net of course and lots of my key words kept leading me here. I have spent hours and hours reading and cant find my answer. I have always had difficulty with complex electrical systems and i don,t understand the spacing of the mags and coils. I understand three set of three coils will give me three phase, but i have seen different numbers of magnets and almost no one using ferrite mags. I just need a push in the right direction. If there is a web site that deals with this issue or if any one can help i would greatly appreciate it. I want to add that i don,t want to limit my self to a small fridge and a tv, i would like to be able to run a skill saw or such items. I will be buying six or so golf cart batteries to hook up when the time comes. Thank you for reading this, i hope you can help. Aloha Dave |
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=bigislanddave] I just need a push in the right direction. First off, welcome to the 4m; you will likely find all your answers here somewhere. The way it works is you ask speific questions and those of us that have the knowledge and experience will then chime in with suggestions. First off, manufacturing electricity from wind involves a pot full of trade-offs. There is no right way, but there are a lot of wrong ways and it's more a matter of familiarization with how things work than a bunch of rules written in stone. First off, a VAWT is traditionally a low-power system and comes in two forms. One form, called a "drag" machine, is basically one or more large paddles in the wind and the air flow basically pushes it at or just less than the speed of the wind. The other form of VAWT uses wings that develop lift and "fly". These propel the shaft faster than the drag type, but nowhere near as fast as a HAWT, which stands for Horizontal-axis wind turbine. A sub-category of the VAWT is the "gyro-mill" which uses a tail to orient a cam, which in turn turns controlling surfaces on the blades or the entire blade such that it does not drag as it travels upwind. In all these cases, you trade speed for torque and I'll even go as far as to say power for sensibility. I build toys for the most part and though the ideas are sound (mostly) the application falls short of what you're likely after, so don't necessarily do as I do. Golf cart batteries are deep cycle creatures and can handle a large load. My advice would be to use a HAWT if you are after reliable, useable power and experiment with the VAWT for now. There is more information on building a successful HAWT than a VAWT. As for choice of magnets, wire size and coils, etc. here's the way that works: Neodymium magnets are very powerful and very expensive. Ceramic magnets, like your microwave oven magnets, are less powerful and likely free. If you're not swimming in cash, go for the ceramic ones for sure. Here's the trade-off: you'll get less power from the ceramic magnets UNLESS you build around it. By that I mean you can up the size of the magnets, the wire size, the diameter of the rotor, its speed, etc. Wire size depends on what you want out of the system. 18 gauge wire can handle only so much amperage before it burns, so that is your limit. It would be better to use larger wire, but there's another way to get around this, if you have LOTS of #18 wire and that is to wind your coil with more than one wire. If you use two wires, it's called two "in hand". This effectively doubles the amount of amps the setup can hold, but by adding more wire, you limit the number of turns you can place in each coil. It's one of those trade-offs I told you about earlier. As for coil size, using a round coil, you'll want your coils' hole to be approximately as wide as your magnets' diameter and each leg of each coil to be about as wide as your magnets are wide, assuming you're using round magnets. The space between magnets should be such that as one leg of a coil is passed on one side by a north-facing field, the other leg on the same coil sees a south-facing field pass over it. The individually-insulated coils can actualy tough each other in the stator without harm. I'm sure someone else will chime in with a better description than I've concocted here (I hope!). Anyway: Study this link and you'll see how arranging things this way will give you the maximum electricity generation. What you specifically DON'T want is for the same field orientation to pass both legs of the same coil at the same time as it induces the same current into each leg, but in the opposite direction, which cancels the current to zero. This is called "cancellation" and it must be avoided or you wind up with nothing more than a spinning yard ornament! It is best to use a 3:4 ratio of coils to magnets and the most common layout is 9 coils and 12 magnets. If you're building an axial-fux rig, that will be 24 magnets, because you place two magnets across from each other. The space between is called the "air gap" or "air space" and its dimension is usually 75% of twice the magnet's thickness. For example,if your magnets are 1/2" thick, 2 x 1/2 = 1 and 75% of that means your gap should be 3/4". Your coil array must fit within that space and clear the sides so that means in reality it will be even less. THAT's the space your coils must occupy. Once you know how large to wind your coil, you make a test coil of any size wire and just wind say, 100 turns, then spin your rotor around it to see how may volts per turn that coil makes and adjust future coils to make whatever voltage you want. Coils can be wired in series and parallel within the stator to achieve what you want. If you wire one leg of each of 3 coils to one contact and then land each of the remaining three wires to separate contacts, it forms what most here call a "star" connection and produces alternating current, which can be "rectified" using diodes, then used to charge your battery. It will take slightly more voltage than your battery is rated at to charge it. For a 12 volt battery, that'd be about 13.5 volts to be safe. If you go way past the voltage, it'll still work, but your stator will heat up to the point it may burn, then you're back to square one. See? Lost os stuff to think about. So, mull it over and when you're ready to build, ask a specific question and give as much information as you can and some or all of us here will try to lend a hand. For starters, what is your average (measured) wind speed? What is your measured electricity usage now and what do you want it to be using wind? What materials do you already have and do you have enough magnets and wire to make a full stator and rotor? Do you have a lathe? Do you have a welder? Anyway, you see what I mean. I hope this gets you started in the right direction. The ball's in your court now; give us some specifics and we'll try to help you out. Best wishes. . . . . . Mac 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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