Here's a small alternator I built that can be easily coupled to a windmill. Actually this unit is too small to generate useful levels of power and is seen here being manually driven to light up an L.E.D. ...
...The eight pickup coils are each made of 90 turns of 28 SWG enamelled copper wire. There are 16 magnetic poles on the rotor, with steel shims shorting out their flux on the opposite side ot the disc. Small commercial wind turbines are built on similar lines, but usually have the magnets arranged cylindrically on the outer rim of the disk with their poles facing outwards. This gives a higher relative speed between the coils and the magnets for a given r.p.m., resulting in increased E.M.F. The a.c. output from this test model can swing from +4V to -4V, when driven fast.
Regards
Joseph