7 Foot Axial Flux Wind Turbine
Since this is my first wind project, I decided to work on something that is a bit easier to construct than a high-output “dual rotor” design. I also didn’t have a lot of metal fabrication shops available to me, so I was looking for something that required little fabrication.
A Volvo brake rotor has become popular among homebrew windpower enthusiasts because of its wide availability and its relative ease of modification. Volvos have a reputation for being long-lasting and their rotors are not much different. A trip to the junkyard landed me with a $20 Volvo 340 strut (rotor, spring, and everything).
A single-rotor design only has one set of magnets that spin in front of a stator coil. This makes construction easier and less dangerous since you don’t have to use “jacking screws” to bring together two magnetic disks. This is dangerous because if you slip, you could very well break your hand or finger. With a single rotor design, there is much less chance of this.
One thing that many people don’t realize about wind turbines is that the blades of a particular turbine are matched to its generator. This is all based on what is called “Tip Speed Ratio” or TSR. By matching the correct blade diameter to your generator, you ensure that the turbine will start generating at certain wind speeds. By having the right size blades and generator, the correct RPM and torque will be produced to generate the maximum amount of power safely (that is without overheating or over-speeding the turbine). Matching the blades to the generator is a very important aspect of designing your windmill, and many other aspects of the machine are based on the blade diameter.
For this particular design, the blade diameter should be around 7 feet.