Axial Flux Alternator


Axial Flux Alternator

The axial flux alternator (sometimes called a generator), is the heart to many diy wind turbine projects. While a small permanent magnet, D.C. motor, such as the Ametek 30, makes for a very quick and simple project assembly, these motors are becoming very difficult to find and quite expensive. Ebay is loaded with people selling D.C. motors for home wind turbine projects, that simply will NOT work, due to the extremely high RPMs required to get any usable output. Thus a homemade axial flux alternator may be your best alternative.

What is an Axial Flux Alternator?

A permanent magnet alternator generates power by passing magnets past a group of coils of wire. The magnetic field that surrounds a magnet is call it's flux. Axial Flux simply means the lines of magnetic flux that past through the coils of wire, travel along the "axis" of the turning motion. The other type of magnetic flux in an alternator is called RADIAL FLUX and it occurs when the flux occurs "around" the magnet. Pictures are worth a thousand words:

Radial Flux

Axial Flux Alternator

In the left picture, the yellow disk is the stator. The two bluish plates rotate, along the horizontal axis, past the stationary stator. In the image to the right, the stator is on the case. The rotor, on the axis, rotates "inside" the stator. There is a guide by Hugh Piggott which describes the process in good detail.

Overview of the Complete Process - Building an Axial Flux Alternator

In February 2001, Hugh Piggott created a guide for building a permanent magnet generator (PMG) (alternator), after being commissioned by the British government. This guide remains in the public domain and provides an excellent overview of the complete process. You can build a PMG from these plans, though these instructions continue to be improved upon. The PDF document can be downloaded here: PMG Manual

This manual describes how to build a 'permanent magnet generator' (PMG). We can
also call it an 'alternator', because it generates alternating current (AC).

The stator contains six coils of copper wire, cast in fibreglass resin. This stator
casting is mounted onto the spine; it does not move. Wires from the coils take
electricity to the rectifier, which changes the AC to DC for charging the battery. The
rectifier is mounted on an aluminum 'heat sink' to keep it cool.
The magnet rotors are mounted on bearings, which turn on the shaft. The rear rotor is
behind the stator, and enclosed within it. The front one is on the outside, fixed to the
rear one by long studs which pass through a hole in the stator. The wind turbine rotor
blades will be mounted on the same studs. They will turn the magnet rotors, and move
the magnets past the coils. Magnetic flux passes from one rotor to the other through
the stator. This moving magnetic flux is what produces the electric power.

Enhancements to Hugh Piggott's Design

Dan Bartmann and Dan Fink, as well as others, have continued to build axial flux alternators and improve upon the original design. Dan and Dan maintain the Otherpower web site which includes additional details on how to build one of these alternators as well as links to their book on this subject. After reading Hugh's PDF document a couple of times, this is your next step.

Take a look at the complete project. Yes, the first time or two that your read through this process, it can seem rather complex and LARGE. However, Dan & Dan provide instructions for the person who wants to build several alternators. Personally, I would modify some of instructions for my own use.

coil winder

For example, I would not build a coil winder with a custom metal stand and metal handle - wood works for me.

Here's the link to the OtherPower website where you can find more info on how to build an axial flux alternator as well as the wind turbine blades and metalwork:

OtherPower - PMG

Additional Resources for Axial Flux Alternators

AxialFlux technical group on Yahoo


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