Basic coil questions
- Hello to the group-My name is Scott and I am working on a VAWT design. I found out about axial flux alternators from Hugh Piggott's book and am ready to construct my own. I have decided to use 8" disc's with 12 neo-wedge magnets. I need some help in understanding the coil wraping and wire size choices.
With my alternator design, I am trying(like most of you) to get usable battery charging voltage 14.5VDC, at the lowest RPM I can. I understand with thin wire and more wraps I can expect a faster cut in speed but excess heat on the other end. I have designed my turbine to control the max RPM it will spin in a given wind. I can keep the RPM around 500-650 even in 50 MPH wind.
So can any of you help me understand what the limitations really are with thinner wire? If they work great at lower speeds but soon heat up at higher RPM's, how fast are we talking about?
My other question is cooling the stator with air flow. I understand a downfall of any generator is power being converted to heat and what to do with it. If I am experiencing high wind speeds(40-50MPH) and that is causing my stator coils to heat up, isn't it also receiving 40-50MPH wind across it? It seems like VAWT design is more suited to air cooling through the plates than HAWT would be.
I know these are very basic questions but anyone's expertise or suggestion would be greatly appreciated!
- 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)