Idea for Very Low Wind Speed Generator

[windygen]

I've monited wind speed at our property for about a year (about the same amount of time I've been reading this excellent discussion board) and I'm very dissapointed that wind speeds are only about 5-10 mph about four months out of the year and 6-12 mph the other seven. I still feel driven to put together a wind generator. My thinking (such as it is) is to go with two 16" diameter rotors with 24 neomags each and have 18 coils. I know this would be unwieldy on a HAWT, but I'm one of those oddballs that is attracted to building a VAWT anyway. Based on the models I've built and tested, I'm thinking a max 200 rpm at 12mph wind speed. how do I determine the wire size and number of windings for a 24v machine?

[Flux]

I don't do VAWT's, I won't be responsible for the project failure but if you supply the details you think you need such as input power and speed I will try and help with the windings.

You will need to supply power in and rotational speed at at least cut in and one load point.

Flux

[windygen]

Thanks for being interested. I am thinking that power in is a variable because I can scale-up the turbine. In other words, I'm starting with the alternator and then figuring a way to drive it. As to cut-in, my best guess based on the models would be around 70 rpm. I found that I could apply a load at that speed without stalling. I know that I'm upside down in figuring this thing, but it seems to me a more direct approach to build the alternator, then fit the turbine. Being a newbie, I need some direction in determining a "load point." Thanks for your patience.

[Flux]

No you can't do it backwards unless you make it so that you can reconnect it for umpteen voltages. The power out will be related to wind speed and turbine speed. If the turbine power is not what you wound the thing for the speed and voltage will all be wrong for the new attempt.

If you have the turbine then build yourself a prony brake, measure torque and speed and find out how much ( or how little ) power you really have and at what speed.

Two bits if wood clamped round the shaft will be more than adequate to measure the power. Speed will not be so easy but if your 70 rpm is near you can count it.

Flux

[windygen]

Ok. Thanks for the advice. I'll retreat, build a full scale model and prony brake and get back to you. Thanks again!

[TheCasualTraveler]

Just a couple questions,

Why a VAWT?

     Is it because of your location, in an urban area? Is it because of the size alternator you plan? I'm no expert but from what I've done with VAWT's I think 200 RPM's in a 12 mph wind would be what you could expect unloaded, or at least in the ballpark. Add that huge alt you plan and I wonder if you'll ever see cut-in especially at 24 volts.

Just how much power do you expect to get to make your work worthwhile?

     Although your wind is not great, 8 to 12 mph winds with a HAWT can still go a long way to keeping some batteries topped of for emergency or occasional use. Maybe more depending on your skill, your site and the efficiency of the alt.

Just my opinion,

[windygen]

I'm certainly no expert either. But my thinking is that in limited wind speed, the best way to move magnets faster past coils is to increase the stator diameter. The engineering difficulties of a large stator and the presupposed torque requiremnts just seem to me to point to a VAWT.

I can't be more specific yet.

[Flux]

"the best way to move magnets faster past coils is to increase the stator diameter."

Increasing linear velocity gains you nothing. The angular velocity is not changed and the volts remain the same. All the larger diameter does is let you use more magnets. It is the increase in number of magnets that gains you something.

Surely the best way to move magnets past coils faster is to increase the rotational speed ( angular velocity). With increased speed the torque falls for a given power and everything points to a HAWT .

I see no real difficulties with a larger stator but I also see no need for it to be big unless you want lots of power. If you want lots of power in low wind then you need a large swept area and the alternator problem will be insignificant compared with the blades.

Flux

[windygen]

Thanks for the clarification. I can see that until I do some real hands on, it's going to be tough for me to get a grasp of the complexities of the relationship between the turbine and the alternator. At least you confirm that more magents, more coils means more power in low winds, and that's what I'm after. I hope to do a full scale model turbine out of PVC and get torque measurements with a prony brake over the next three to four weeks.

[vawtman]

Hi fellow oddball windygen

 How big were the models you built and tested?

[windygen]

One foot diameter by three foot tall.

[windygen]

Somewhere on this website, I read that using the same number of magnets and wire as two alternators but in a larger diameter configuration would give me four times, rather than just twice the power. Is this in fact the case?