wind generator blade speed

Okay. now I have a grasp on my amp (or should I say watt) draw. I now need to figure how to make this wind turbine produce what I need. I've bought a small 200 VDC motor to build my first turbine from. This is just my 1st hobby wind generator to see if I can & how well. Probably the wrong one, but it's cheap enough and sure I'll use it for something in the future. 400 rpm seems really fast to generate 12v! So that's my first question... is it? To achieve this speed , in my area (Class 2) I can expect 4 hrs a day wind of only 3-7 mph (trying to stay very modest), so I assume I need multiple blades and gearing. 2nd question; How do I determine how many blades, of what size I should make to obtain a certain rpm in a particular wind speed? Not sure I asked that correctly, so please bear with me. Once I have this generator in hand I will be able to measure the torque needed to turn it. Then I assume I need to determine a blade size and count to meet this need. If that is still not enough, I assume I will then need to gear it and re-calculate the blades. Anyone out there have the math to figure this?

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NachoMahma9 years ago
. Try Google.
olddawg (author)  NachoMahma9 years ago
Did that and probably didn't ask it right..... Reason I'm asking here were folks have been through most of this before...
Patrik olddawg9 years ago
Googling for wind turbine design gives a *lot* of useful hits.

Note that this is a very well studied area - lots of commercial and DIY wind turbines aroun - so there is quite a bit of literature on the subject. Check your local library - chances are they'll have a whole shelf full of reference books on the topic...
Hmm I've been experimenting with widn generators or more importantly the turbines used, so far I've noticed that older style 'farm' windmill turn fast even in lower wind speeds and are very ignorant of balancing etc. One that's badly bent still runs pretty well... Savonius seem to be good but have a top out speed where they wont go faster... Want to try a big spiral turbine next... This is only my experience in the matter, I'd do a bit of reaserch on the best way to get power from your machine...
olddawg (author)  killerjackalope9 years ago
I've looked at several different styles or should I say approaches. I'm leaning away from a savonius style for I just don't see that kind of speed or torque. I could be all wet about this and would love to be corrected. I saw an instructable were a bicycle tire rim was used as a rotor and blades weaved into the spokes. The experiment was cool enough, but it raised thought of how well it could work in low wind speeds and it adds a dimension of gearing I never thought of before. Plus the ratio of rim size to motor shaft size. I may have found a use for that old 12 speed bike I have in the basement. Torque seems to be the biggest question right now. If the motor takes 1lb (example only) to turn, then would a gear 6x the size take 6x the torque? Seems reasonable, but I'm hoping the math tells me it takes fractions there of. Anyway, thanks for the response and I'll find a way to post up my trials.... hopefully accomplishments.
Yeah though some form of auto gearbox could be formed using those umm whirligigs, you know two balls on a thing that, eh I'll find a picture and how they're used, they were an old time solution to governors etc. they lift a collar at a certain speed so you could adapt for this...