Hi Scott --
Likely the axial flux PMA is *the* best choice for your VAWT, actually
-- nothing else out there combines low-rpm direct drive performance
with ease of construction. You could mess with laminated coil cores,
but that is complicated and hard to fabricate, and I can't predict how
much cogging will affect your VAWT compared to a HAWT (in which it's a
killer in low winds).
The lower your RPM at the shaft, the bigger and more expensive the
alternator needs to be to make the same power as a higher rpm. We here
at Otherpower could easily design you an axial flux PMA that makes
1000 watts at 40 RPM -- but you are NOT going to like the cost of
Scott, have you measured shaft torque vs. RPM from your VAWT blade set
in the wind yet? This is where most experimenters run into trouble (by
not doing this, and instead using unloaded RPM for their
calculations--RPM in the wind with no load on the alternator is not
very useful information after the alternator cuts in). My apologies if
I missed this in this thread. If NOT -- rig yourself up a DeProny
brake and start plotting the curve. Mount the VAWT to your truck, etc.
and you can test torque vs. rpm at different wind speeds.
Have fun -- I don't really mean to discourage anyone from building a
VAWT, but I *do* like to explain why they cost much more to make the
same amount of energy per month.
I would be happy to send you the NREL chart on possible efficiencies
of different turbine blade designs; actually I'll try to post it on
the archives if i can figure out how. It's in my book too, page 63,
you can nab that free from Google Book Search.
co-author "Homebrew Wind Power"
(snip)This took me and my partner many hours of work to get to this
point with the design. I feel it has far reaching possibility's for
future VAWT. But I'm in uncharted waters and need some honest
impressions about this. Can I really build an axial flux generator to
do what I want or do I need to shorten my scope and go with a
compromise? Scott (snip)