Project Journals > Chris Olson
3.2 meter ferrite magnet MPPT wind turbine
ChrisOlson:
--- Quote from: WindyOne on November 27, 2012, 10:23:13 pm --- Why did you decide to use ferrite magnets vs neo's?
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They're a lot cheaper. Less than $1 for a big 2 x 2 x 1" thick magnet vs $8 for a 2 x 1 x .5" thick neo magnet. The neo magnets were double that price when I built the first ferrite generator. They have come down in price some now.
--- Quote --- Would a 2.5 times more powerful neo magnet allow the elimination of the 1:2.5 transmission?
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Yes. Although I have also used the transmissions on neo magnet turbines as well. Using the gearing allows you to develop the same power with a smaller and lighter (and cheaper) 12 pole generator instead of using a 16 pole on a 3.8 meter turbine, as an example. So it still cuts the cost of the magnets because you don't have to use as many of them.
--- Quote --- Did having the transmission make anything easier or better?
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The electrical efficiency of the generator. Since I started building geared turbines about three years ago now, I have not been able to build a direct drive one that can match the efficiency of the geared ones. Especially with axials - the bigger you make an axial the bigger around it gets and the more copper it has in it. The more copper you put in it, the higher the internal resistance. You can even double the copper up (two-in-hand windings) and can't match the geared ones with a single winding in delta.
Hugh (Piggot) built a new design ferrite magnet direct drive turbine in the 3 meter class using my "pole cramming" method to keep diameter and weight smaller, after he saw that it works. His turbine is pretty respectable from homebrew standards as compared to contemporary neo designs and it puts out about 750 watts. But not even close to the 2.5 kW I get out of my geared ones.
--- Quote --- How much of an issue is corrosion with neo's?
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Pretty bad in some cases. Ferrites can rust, but they never bubble up and form white balls of corrosion like neos do. The only thing that protects neos from the weather is the coating on them. Sealing them in resins doesn't work because moisture trapped in the resins during casting gets in, destroys the coating, and they bubble up and fall off. Neo magnets are very, very fragile.
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Chris
WindyOne:
Chris,
In your message dated "January 12, 2012, 04:30:25 PM" on page #1 of this thread there is a photo of your coils laying over the magnets. It appears that the "leg / side" of each coil is not parallel to the adjacent coil's leg. The outer shoulders of the coils touch but the inner shoulders have considerable space between them. This means the "legs" are not on the radius line (magnet center line) and are not 90 degrees square to the motion of the flux passing by. Do you know if this "angling in" of the legs causes any decrease in voltage produced or not? Less wire at the "V" means less I2R power loss in the coils - that is a good thing. How important is it that BOTH legs of the coils run down the exact Center-Line of the North and South poles when that coil is aligned with two of the magnets?
Do you bond your coils with super-glue or just the tape them?
Can any product be added to the coil windings, before being installed in the stator, to help them transfer the heat?
What is "pole cramming"?
ChrisOlson:
They don't have to be "square" with the flux because if you look at the flux with a gauss meter it's a mess anyway and doesn't follow anything to do with the magnet shape or orientation. It works by linking flux from one pole to another and the change is what induces the current. Skewing poles or coil legs provides a sine wave with slightly less amplitude, but it's flatter so the voltage produced stays above the point where the rectifier stops conducting longer, which is better for battery charging.
I just tape the coils and put a lot of glass in the stator. Glass transfers heat really well - plastic (resin) doesn't.
Pole cramming is fitting the most poles possible in a given diameter instead of using spacing that theoretically produces more flux in the air gap. Hugh used to think that you have to space the magnets far enough apart to prevent "wasting" magnet surface area, and have a coil hole at least the size of the magnet. Which is true to an extent, but that ends up with the result being spacing between coils and adding resistance to the stator. The gains by reducing resistance and ignoring the very slight voltage drop by "wasting" magnet surface area with smaller coil holes and a wedge shape is greater than the "accepted" way of doing it in all the homebrew books.
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Chris
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