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Small Wind Generator/Motor
sr71p38:
Wow! Thank you so much for all the responses. This is some awesome information.
I was going to reply to each but not sure how to do that just yet. So I am able to get the 1000 rpm but I have to get upwards of a 26mph wind to do it, which seems really insane to me. I did cheat and use a drill at one point to make sure the motors were doing what they said.
It seems by some of what was said below this RPM might not be crazy. I was reading that many of the wind generators on the market produced their rated power output at 90 RPM in 10 to 15 mph winds. Or is this complete rubbish?
The diameter is small about 15" with 6 blades, which are all custom designed, which are direct drive to the permanent magnet motor. They are using two high-energy saturated C8 ceramic magnets. The system is set up as a traditional horizontal axis system. I am using a bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt which is right before the 12volt batteries.
Maybe it needs to be geared, as motors this small seems to need to run at these higher RPMs. It sounds like even a custom-built motor wouldn't work.
To answer one of the questions, yes I am a pilot and very much an aviation enthusiast. Yes, the SR-71 takes it every time. I got to see it fly once. The P-38 is a really underrated bird and was a workhorse of its time! The link was they were both designed by Kelly Johnson.
bigrockcandymountain:
I like the Hawker Hurricane for the same reasons you like the P38. You'll find lots of aviation enthusiasm here. It seems to be a common interest with wind turbine people.
90rpm in a 15mph wind is quite normal also, depending on diameter and tsr (tip speed ratio).
A normal tsr is between 4 and 8 for a horizontal axis turbine with airfoil blades. A 6 blade might be the lower side of that si lets use tsr 4 for your turbine.
In a 25 mph wind at tsr 4 your blade tips would be doing 100mph. (4×25) This is 147 fps.
At 15" diameter your circumference is 3.9'
147' ÷ 3.9 = 37.7 rev/second or 2261 rpm
So if you do half the wind speed it should be half the rpm or 1130 rpm at 12.5mph.
That isn't what you are seeing though correct?
Maybe your blades are 15" so your diameter is 30" or maybe they are just the wrong angle of attack. Wind turbine blades stall, just like airplane wings. If they are set too flat to the wind with not enough downhill, they stay stalled and won't make power.
Welcome to fieldlines. I'm glad you joined. Hopefully we can get you making some power. It gets really fun when the watts start to flow.
Cheers
Derek
Ps I fly an antique Aeronca Chief off of a dirt strip.
sr71p38:
Derek,
No, I am not seeing what you have calculated below at all. I have been using Digital Photo Sensor Tachometer that I got from Harbor Freight to check the RPM. When there is no load or no batteries attached I can get 500 to 600 Rpm with an 11mph wind, I use a handled wind gauge to measure this speed. Once a load is applied it goes down to about 300 rpm. I am measuring on the blade hub, so not tip speed, which might be one issue.
I doubled checked the diameter and it is 16", in a 25mph wind I should get 2,100 rpm, I am not even close. The blades are 3d printed with a 48-degree pitch.
It seems what I am seeing is a little more than half of everything theoretical. if I do a 25 to 30 mph I get the 1000 rpm but should see a lot higher. Or with an 11mph I should be at 1000 rpm and I see 300rpm with a load and 500rpm without.
Regards
David
PS. a taildragger on a dirt field that is impressive.
bigrockcandymountain:
48 degree pitch is your problem. Most turbine blades are around 4 degrees. Really high speed ones are even flatter.
bigrockcandymountain:
Oops, missed your ps. Yes, it is a different skill set than nosewheel on pavement that's for sure. The soft surface makes the taildragger easier to control actually.
What segment of aviation are you part of?
Can you heat and twist your blades flatter on your turbine?
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