Homebrewed Electricity > Wind
Appropriate generator characteristics for small wind turbine
Adriaan Kragten:
--- Quote from: SparWeb on February 16, 2024, 11:15:31 PM ---Hello Lars,
Have you set up with wind turbine outdoors in the wind yet?
NEVER RUN A WIND TURBINE UNLOADED.
--- End quote ---
If it isn't allowed to run a certain wind turbine unloaded, there is something seriously wrong with the safety system. The safety system which limits the rotational speed and the thrust must be that good that even an unloaded rotor won't be destroyed at high wind speeds. Reduction of the rotational speed only by the load is dangerous because the required electronics to steer the load may fail and this results in an unloaded rotor.
I have tested the hinged side vane safety system of my VIRYA-4.2 wind turbine with an unloaded rotor and although an unloaded rotor is rather noisy, the rotor running at the maximum rotational speed gave no problems at very high wind speeds. The VIRYA-4.2 has a 2-bladed rotor with a diameter of 4.2 m with constant chord blades made out of massive mahogany wood. The design tip speed ratio is 8 and the unloaded tip speed ratio is about 12.8. The blade chord was 200 mm and the Gö 623 airfoil was used. The maximum unloaded rotational speed was about 480 rpm, so 8 rev/s. The maximum loaded rotational speed was about 300 rpm so 5 rev/s. The slender blades of this wind turbine are sensible for flutter at very high tip speeds but flutter didn't occur for an unloaded rotor.
kitestrings:
Hi Lars, and welcome.
You have a really sleek looking turbine; some nicely printed pieces for sure. I hope to see more as things develop. You've probably already figured out that you'll get a wide range of perspectives here on any given topic, and the trick is to wade through them. In the end though, I believe it helps the design process. The comments have been good. I don't have a lot to offer, but for what it is worth...
I think your blade connection at the hub may be something you have to beef up. I'd be concerned that the reduced width might be a weak point without added thickness or some sort of strut.
A couple of us here have been using MPPT type controllers (Midnite Solar, Classic). They are not a true "feedback and adjust" as with solar, but rather they allow you to input a power curve that follows the curve of the alternator. One benefit though, is that the curve can be tweaked, if it is not perfect from the start.
I do agree that it is best to attempt to keep things electrically loaded to the extent possible - I think that was Sparweb's intended message. Side-furling works well. It's time proven. If a turbine runs unloaded, in a good wind site for any amount of time though I would say it is only a matter of time before something fails. It will spin up to rpms that it is not equipped to handle, furl, slow and repeat. To touch here on that "wide range of perspectives" I mentioned earlier, here's a prime example where we get deep in the theoretical discussion on the one hand, but then make broad-brushed summations based on very limited, antidotal experiences on the other.
Good luck, and I hope to see more, ~ks
JW:
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