How many turns on the coil / typical RPM?

[Ekij]

There are a lot of variables when making a wind turbine, most turnbines appear to be either tiny demonstrators (useless power output) or serious 10' machines, I'd like to make something somewhere between the two for my first machine.

To this end I've no template to work from, no-one to copy.

I've decided to make the alternator first and then I can make a couple of passes of blade design if the first turns out ot be too big or too small.

However how do I know how many turns to make the coils?

Assuming I make the PMR (Permanent Magnet Rotor) and one coil I should be able to mock-up something on the bench to give me an idea of the Voltage available from this coil to decide whether or not it needs more (or fewer) turns for my desired rated voltage.

Average wind speed is typically 12mph (5.3m/s) but how to I relate wind speed to rpm to do my bench test and select the number of turns on my coil for my desired voltage?

Is it appropriate to assume that rotor tip speed will be roughly equal to wind speed (at 12mph)?

So if I'm looking at a machine about 0.4m blade diameter, producing 12V with 12mph winds, hopefully capable of 240mA at this speed, I should be testing my first coils at an rpm of about 92?

(yes I'm aware that an off load voltage of 12V won't be able to charge a 12V battery)

Can anyone give me some idea of how many turns I'm looking at 25/100/400?

  Ekij

[ghurd]

I believe you will need to go larger because the space to work in something that size is almost not enough.

Magnet disks under about 125mm are not easy.  That uses up 1/3rd of the diameter of a 4.6 meter diameter machine.

The inner 1/3rd of the blades is not normally considered a big deal, but to scale that is 1 meter magnet disks on a 10' machine.

Even 0.6 meter (24") diameter is tiny.

Could work backwards through Ben's little PMA Diary for a lot of relative info.

http://www.fieldlines.com/story/2009/2/26/213016/068

Can not get anyone to guess about coils until you have the magnet size and count.

Magnet size, number of magnets, and space at the center will show how fast something 100mm gets too small fast.

G-

[Ekij]

Thanks for the quick response. I was thinking of 12, 10mm dia Neodymium magnets which would fit comfortably on an 8cm wide disk. (or 8 * 10mm magnets on a 6 cm disk)

Why do you feel a <125 magnet disk isn't easy?

[ghurd]

Sounds like a somewhat perfectly done assebly will have about 35mm to work with in the center.  That is for axle, bearing, adjustment screws, jack screws, spacers, or whatever the design has at the center.

There is not much room for any errors.  Something like the coils springing out a bit messes up everything.

I am not the only one who had big problems with little disks.

http://www.fieldlines.com/story/2008/12/20/18329/862

G-

[jaskiainen]

Hi Ekij!

I made my first mill with 12x3mm Neo magnets on about 70mm disks.

I hope now that the discs would be even 80mm now cause lack of space for coils.

I managed to squuze in 110 rounds per coil, but its not enough.

130 rounds would be more like the correct ones. Only missing some space.

So now I need to order another set of magnets and glue them on top of the old ones.

Don't get me wrong here. I'm getting nice watts out of it in good winds

(around 60watts so far. Thats 4.6amps).

Just don't want you to make same mistake than I did.

Ghurd might remember this one.

Just start with about 100mm discs for tiny genny (10-12mm magnets?).

If you decide to make a genny that size then I might be able to help you?

Read anything you can from here to get a good picture what you are doing.

And ENJOY THE RIDE!