The 6" diameter axial flux alternator
This was a nice project, some will be familiar with the larger versions, this is a smaller lower powered unit.
This is a three phase, twin-rotor axial-flux, air-core alternator design, as pioneered by Hugh Piggott.
The beauty of this design is that it doesn't suffer any of the 'cogging' issues that can hinder other designs.
This alternator uses a fixed stator, housing the copper wire coils embedded in resin with two rotor plates
top and bottom holding the very strong N40 Neodymium magnets. (19x12x6mm).
The rotor diameter is 6" (150mm); dual rotor design, 12 magnets top and bottom, 9 coils, 130 turns each, 3phase.
Output is 50 rpm per volt (33 rpm/V in star) - 450rpm (in star) for 14V output.
Performance was not as good as I thought it would be, generating approximately 2 amps @12 volts (24 watts), but no cogging and very easily spun.
This alternator could have been considerably more powerful if the stator was made thinner, decreasing the 'air gap' to increase the magnetic flux.
The video below shows just how well the alternator spins.
Further reading - An excellent PDF on the 'Basic Principles Of The Homemade Axial Flux Alternator' here (782Kb)