Index (in reverse order so the latest stuff is at the top)Coil Performance TestsCoil Winding Alternator Construction Alternator Design Alternator Conceptual Design References Back to the Overview Coil Performance Tests, 21 May, 2006I have begun the slow process of testing the coils I've made inside the alternator. Measuring voltage and current across loads will give me lots of useful info about coil size vs. performance.
I will repeat the test using different speeds, sizes of wire, magnet spacings, etcetera. Hopefully I'll be able to make sense of all the data when I get through it all. Coil Winding, 23 April, 2006With the wide variety of wire sizes available, I haven't been able to settle on the right gauge to use for my experiments. Lighter wire will allow more turns, capturing more voltage. On the other hand, heavier wire will carry higher currents. Choices, choices.To figure out what to do, I'm winding some test coils to get some "preliminary results", and will base a final decision upon that. To help with the work, I've built a coil winder out of some spare parts. If I were to go with fine wire, I could be facing 12 coils of 200 turns each. Some people are willing to hand-crank something 2400 times, but I'm not!
If you take apart a microwave and all you find is a low-voltage motor, you'll need to pull out the little transformer (not the big one) to step-down the volts. The motor currently being used (120V, 6RPM), probably won't have enough torque to wind heavier gauge wire. 18-gauge, and 20-gauge seem to be fine. There are a wide variety of microwave motors out there, so you may find a slower one, which may have more torque. The larger the micro you get it from, probably the better. Microwave motors are "synchronous motors". That may not sound important, but there's something to bear in mind: microwave motors can turn in EITHER direction. All you have to do is give it a twist as it's turning, and off it goes the other way! If it gets blocked in one direction, it will just turn the other way. That means that if something gets stuck in your winder, you will suddenly find your bobbin UNWINDING, and wire coiling down on the floor! Alternator Construction, 14 April, 2006I've been cutting parts for the alternator in between all the other things to do these days. I'm ready to start winding the coils.
Alternator Design, 28 March, 2006I've progressed to turning my conceptual design into reality. Keeping it small, my alternator design is a compact 9" in diameter. The rotor (left) has 16 magnets. Their poles will alternate between north and south. Two identical rotors (with opposite poles) will face each other when assembled. Between the 2 rotors is the stator (center) with 12 coils inside. These coils will be wound with wire and three groups of four coils each will be connected in series. That will give me 3-phase power to rectify. The hub (right) has 4 bolts (the rotor was drilled with extra, just in case) and when assembled, the magnet rotors will be squeezed between the hub and the windmill blades. Enough of a gap will be left between the faces of the rotors for the stator to sit. Conceptual Design, 8 March, 2006Windmills that produce useful electricity can do so with a variety of ways. I've opted to build a permanent-magnet axial flux alternator. Many other wind-power enthusiasts choose this type because modern hi-power magnets make it efficient and easy to make for the homebuilder. Instead of a cylindrical core inside a shell wound with wire (which also works as an alternator, by the way), a flat disk turns beside a rigid plate. On the rotor disk are magnets, whose poles alternate. Inside the rigid stator plate is an array of wound wire coils. The magnets on the rotor spin past the coils of wire on the stator. As the rotor turns, the field changes rapidly from north pole to south pole. The changing magnetic field induces a current in the coils of wire.My approach has been to learn the physics before building anything, so I've spent the past month using software and textbooks to figure out how it works. I discovered a fantastic package of software on the internet called "Finite Element Magnetic Modelling", or FEMM. It works, I finally understand it, and the results are detailed. Here are some samples:  The magnets are placed on a steel rotor disc that is turned by the mill. The stator is fixed and contains all the coils of wire.  The field lines around the magnet are distorted by the rotor disc. Little escapes out the back of the rotor, which is good. More magnetic field is concentrated through the stator to induced electricity in the coils. Building on this, I've created a computer model of the alternator's performance. I can change variables of the alternator's design and see how they affect its output. Useful results yet? No. I've input data from some other well-documented windmills and the analysis over-estimates the performance by a long-shot. References:I'd like to extend a warm thank-you to all the folks who have offered free advice, inspiration, and contributed ideas to my project, namely Flux, SamoaPower, DanB, Jerry, and many more, from the Otherpower Forum.
Updated 23 April, 2006 Created 30 March, 2006, Steven Fahey |
