coil maths

[racingbrett]

Iv searched around a fair bit but im having problems finding the maths to work out the stator coils, im working on a 24V system with a 3-4 Bft average wind and basically everything is open, nothing is planned yet but id like to create a gen capable of 1.5KW to 2KW. For ease of blade building id been planning to use multi-wing blades (http://www.multi-wing.com).... is this practical and possible.

I ask because for around £160 it is possible for me to buy a reliable tested chinese imported 1.5KW PMA  with low start up and good high wind figures designed for use with blades (1.7m dia 5 blade) from the above company and looking just like a drum brake setup with a splined shaft out the back to bolt onto the wind gen body.

to try match this in a home built machine would i be hunting for a false economy?

Many thanks Brett

[DaveW]

    I've used products from multi-wing before and as far as I know they make fan blades.  Good ones, mind you, but not for this purpose.  The profile is exactly wrong to try to extract power from the wind. I have admired their mounting hubs but they are a little expensive to buy for the hub and add blades to. You can find blades on ebay if making your own is too intimidating at the onset. Some of the people on this forum sell blades that work well and are quite reasonable.  One point that confuses me is the 3-4 Bft wind speed you mention.  If this is anywhere close to MPH, and you are working with 1.7 meter blades, a 2KW output is going to require a lot of wind to make that output.  Something like 35 MPH, with a high TSR blade set and a sturdy tower to hold it all.

    You might consider starting a little smaller for your first attempt, like a 500 - 700 watt machine to get a feel for how it all comes together and what is required.  Then as your understanding and comfort level grows, a larger machine won't be quite as much a puzzle to work out.

    The interaction between rotor size, magnet size and count, coil count and wiring, blade size, and spacing of everything dictates the output, given a wind speed and location. Many ideas have to be addressed at once to understand just the wire size, coil size, turn count, and expected output of a given coil.

[racingbrett]

Cheers for the response, the reason i was looking to the multi-wing blades is because i noticed a fair amount of off the shelf wind gens are now using these blades, including a 1KW one sat in my garage , how well they actually work compared to home made specific designed blades would be interesting to know.

3-4 Bft is actually a large range of 8 - 18mph with the occasional gusts of wind exceeding this (maybe up to 25mph)...

Looking into it more your absolutly right and i think with a better blade system the off the shelf 1KW gen would give better low wind results as well, in the current set up the turbine spins at 490 rpm in a 31.5mph wind giving 34 amps and a battery voltage of 33.6 V, charge initaiation wind speed is 6.8mph.

Anyway back to it, i think if i could design something to give say around 500 to 800 watts within my average wind speeds then id be chuffed at that.

What im thinking along the lines of is as many people have built, a twin neo magnet rotor, single stator built arount a 1" trailer hub and stub wired in 3 phase delta, i was thinking of rotors around 10 - 12" and magnets like available from www.windstuffnow.com..

Back to the reading to figure the rest out

Many thanks Brett

[Boondocker]

I've been considering the same idea of using windstuffnow wedge magnets, 12" rotor, with a trailer hub.  When I lay it out on a 10" rotor there is not alot clearance room for hub bolts to spin inside the stator. The hub bolts are 4" on center and the magnets are 2" long.

Duane

[racingbrett]

i have a question from this comment

""" in the current set up the turbine spins at 490 rpm in a 31.5mph wind giving 34 amps and a battery voltage of 33.6 V"""

So idealy if i wanted to improve this id want a new set of blades that spin at 490rpm in a 20mph of wind, using Altons wind calculator would i be right in saying that i need a 2 meter prop with a tip/speed ratio of 6, angle of attack of 4 degrees, 3 blades, and a coefficient of lift of .8, what i dont understand is this shows me 516 rpm at 20.1 mph but only 421 watts at the blade however the current turbine setup produces 34 amps and a battery voltage of 33.6 V (1142 W) at 490 rpm.

[DaveW]

  With a span of 6.57 ft. (sorry, meters gives me a headache) at 31.5mph you can expect about 1620 available watts with a reasonably efficient setup, at 20.1 mph just 420 watts are available.  RPM aside, you can't match outputs until the wind speed and available power are taken into consideration.  The size and design considerations you work to will have a sweet spot, not all that wide in actual wind speed, and this might not extend up to the 31.5 MPH speed. Best to consider the actual average available and work to that, and furl a little early at higher speeds to save overheating your stator.  I have built 5 machines so far in the 6 1/2 to 8 ft range, and while they will produce 1500 watts for minutes at a time, 750 to 800 is the top end of my safe furl point. Otherwise, they overheat.

[racingbrett]

Thanks for the Reply Dave, the 31.5mph i quoted was based on the generator unit with the supplied 1.8 mtr 5 bladed multi-wing setup. What id like to do is to throw the multi-wing blades to one side and to design my own set to give me a more optimal performance (490rpm) at lower windspeeds say around 20 mph with the furling system cutting in earlyer as you say to save me burning out the stator.