Basic Principles Of The Homemade Axial Flux Alternator If you are new to the topic of building Permanent Magnet Alternators, then this is for you! My purpose is to help people learn about the DIY wind turbines that are gaining in popularity. Basic concepts are introduced here, but it’s still up to you to read on; this hobby is very multidisciplinary! For every topic, you can find a wealth ofadditional information – I hope I can help start you off in the right direction. Those with corrections or suggestions are welcome to contribute.
A Successful 17’ Wind Turbine Design by Dan Bartmann (www.otherpower.com)
Hugh Piggott’s Popular Design Manual (www.scoraigwind.com)
Steven Fahey Version 1 December 18, 2006 Page 1 of 15
Basic Principles Of The Homemade Axial Flux AlternatorMagnets
The Neodymium magnet has been a key technological development that allows practical and efficient alternators to be built. The high strength of Neodymium is part of what makes computer hard drives so compact. Now the material is avaialble commercially for all sorts of purposes. Many sizes now available are perfect for use in the DIY alternators. Below are pictures of some common sizes thatare used:
2” x 1” x 0.5”
1” Diameter x 0.5”
“Magnetic field” is the technical term for the lines of force that are often drawn to symbolize the magnetic field around the magnet. The magnetic field intensity is measured in either Teslas (after the inventor Nikola Tesla), or Gauss (after the mathematician). The symbol “B” is used for the field intensity (like “F” for force,“W” for weight). The intensity, B, gets stronger as you get closer to the magnet, since the lines get closer together. There is always a North Pole and a South Pole. The magnets we prefer to use have poles on the faces with the most surface area. The example magnets shown above are more flat in one direction: the poles are on the broadest faces. Some types of magnets are longer on the polarizedaxis, but an axial flux alternator is efficient and lighter when the magnets are just big enough for the job, and no bigger.
Magnetic Field Lines Around a Magnet When magnets are made, the magnetic poles are “frozen in” with an external electromagnet as the metal cools. If a magnet gets too hot, its strength will weaken.
Steven Fahey Version 1 December 18, 2006 Page 2 of 15
Basic Principles OfThe Homemade Axial Flux Alternator
A few illustrations will improve the understanding of how magnetic fields are manipulated. When magnets are attracted to metallic objects, the attraction can be witnessed by a distortion of the field lines that we saw above. The lines are drawn to that object, in much the same way that the object itself is drawn to the magnet. As the magnetgets closer to the plate, field lines pass through the plate and get stronger. The increasing size of the arrows in the diagrams below illustrates this.
MAGNET IRON PLATE
Flux Lines Through an Object Attracted to a Magnet
Flux Lines Through an Object in Contact With a Magnet
When the plate is in contact with the magnet, the field lines can become very concentrated in the plate. Theyconcentrate themselves in the plate, and if the plate is thick enough, very few lines emerge out the other side. Through the neodymium magnet itself, the magnetic strength doesn’t change much. In a sense, holding a magnet beside the plate of iron is like holding a ball above the ground. The ball falls due to gravity, and it comes to rest at a lower potential energy. Same with the piece of iron; onceit is in contact with the magnet, the potential energy is lower. The magnetic field of the magnets is manipulated in this way. The next illustrations show two magnets that are close together. If similar poles are close together, then the lines diverge, and the effect is felt as repulsion. If their opposite poles are close together, then the lines converge (attraction). As they get closer, more...
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