Tuesday, February 1, 2011

What blades to use on your small wind turbine.

What blades will work best on your small turbine? How many blades should you use?
Well, just from personal experience, it depends on a lot of things, but we'll work with the 3 most common.
1. Average Wind Speed
2. System Volatge
3. Amps Required

Here's my formula based on the K.I.S.S. theory..
The Lower the Wind, The Larger The Blade.
The Higher the Wind, The Smaller the Blade.
The Smaller the Blade, the greater the RPM
The More Blades You Use, the More RPM's You Lose!

First - a little lesson on how this stuff works.
If you are running a PMA (permanent magnet alternator) turbine in a LOW WIND area, your system voltage plays a very important role. Lets use a 12v system for an example.  Low Wind areas are not very productive to be running a turbine, so you will want a turbine that can produce 12v at a VERY LOW rpm. Once it hits 12v (or what ever voltage your batteries are at), just like a car alternator, you will start producing amps/current when you reach a voltage of 14.2v or higher depending on your load or how dead your batteries are. The higher the amps, the faster you'll charge. When the PMA is charging, the shaft will get tighter and harder to spin as the amps increase. A small blade wouldnt be an efficient choice for this scenario.

A low wind / low voltage system is going to want A LOT of amps! So a larger 3 blade rotor with some pitch may be the way to go.You want to be able to create torque without things getting scary! Now you can run more than 3 blades in a low wind configuration. By adding blades, the PMA will cut in earlier and at a lower speed, BUT you may lose amps at higher speeds.

I run a 3x 35" aluminum blade configuration on my low wind PMA. It hits 12v at 130 RPM and it will produce about 12 amps in 15-20mph winds.. It will cut in (start to spin) in as little as 2mph winds.

High Wind areas may want to go with a smaller blade for a 2/3 blade rotor. You may also want to got with a higher RPM PMA that produces 12v at 250-450 RPM. This would yield a little better amperage.

You really do need to play with blade size and pitch because all areas are not the same. You may find that a 28" composite blade may work better for the higher wind areas. But this should give you a ballpark of where you need to be.  I'm happy to answer any questions you may have!

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