Homebrewed Electricity > Wind
Christmas Windmill Time
taylorp035:
So I just took my 46" diameter blade set back outside since we were seeing 20+ mph winds today. The performance was super disappointing as it was really struggling to get the tip speed ratio up and didn't really want to start spinning. I've definitely seen my 8 foot blades spin faster than this. So I think I've decided that a set of 7 diameter blades that are extra wide (maybe 5") and have a steeper angle of attack would be appropriate to meet my rpm goals. The charge cut it did seem reasonable though, even with the 1v drop through the diode. At a nice 10 mph breeze if the blades actually perform well, I think I will see 1-3 amps, which would charge a set of batteries in a day or so.
Even in the highest gusts today, the generator really over powered the blades by a huge margin.
Criger:
That's certainly counter-intuitive, isn't it? At least it seems that way to me. I would have thought the 46-inch diameter blades would get much better performance than that.
SparWeb:
Could you take a picture of the blades, Taylor? I'm puzzled by this, too.
Something should be happening.
If it's the blades I can (sort of) see in your profile picture, the solidity ratio is very small, which is a big detriment to start-up, but at 20MPH should not be a problem.
That said...
"...a set of 7 diameter blades that are extra wide (maybe 5") ..." For a 7-foot diameter blade, 5 inch chord is not "extra wide". 5 inch chord is barely wide enough at the root for such a diameter. For that diameter, the tips should not be less than 2" either.
So on both counts I have some questions about the solidity ratio of your rotors.
MattM:
More stiffness, less angle! You will believe.
taylorp035:
My old blades were 3" wide at the root and 1-3/8" at the tips. They don't have much of an angle at the tips. I originally had 6 of these blades on one hub to help have more startup power, but it didn't work very well either. I took some pictures of it.
I plan on doing a 4 degree tip angle and 4" wide for the whole blade (no taper) and 42" long. The boards are glued together and ready to be carved. They are 4.125" wide x ~2.25" thick in total, made of ash.
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