Wind Turbine: Ratio of magnets to coils?

[Mandy]

In two sources, I've seen wind turbine plans that call for 2 sets of 12 magnets (facing brake drums) turning around a stator of 9
magnets. I get the groups of 3 coils, but is there a reason to limit to 9 coils? Also, what if I want 24/30 or even 31 sets of
magnets/coils? Aside from prohibitive cost, please help me to understand the math here.

Also, what is the best way to search this group's archives?

Thank you.

 

[Roger_Nickel]

In two sources, I've seen wind turbine plans that call for 2 sets of 12 magnets (facing brake drums) turning around a stator of 9
magnets. I get the groups of 3 coils, but is there a reason to limit to 9 coils? Also, what if I want 24/30 or even 31 sets of
magnets/coils? Aside from prohibitive cost, please help me to understand the math here.

Also, what is the best way to search this group's archives?

Thank you.

The alternator is connected as a three phase system to reduce the
cogging which would occur if all coils simultaneously passed between a
magnet pole pair. Draw out the circle with magnets at 30 degree spacing
and coils at 40 degrees and you see that every third coil is syncronised
passing through the magnet pole pairs. Low cogging in the alternator is
vital to allow the turbine to spin up in light winds.

 

[Mandy]

Excellent. I understand. Thank you.

Has anyone evaluated orbital (hubless) wheels for building turbines? Well I'm sure SOMEONE has, but anyone HERE?

Wheel Examples:
http://www.osmoswheel.com/pages/galerie_photo.asp
http://www.powerscoots.co.uk/acatalog/Wheelman.html

And a little off-topic for turbines, but cool wheel-related news (never thought I'd say that):
http://www.michelinmedia.com/naias_2005/html/tech_innovations_rise.htm

 

[paul v birke]

Dear Mandy
Personally I have not seen. will check the patents

Maybe two side by side hubless over a central stationary parts.

Magnets on the hubs and coil on stationary part

Best to have on magnet source spinning and outer hubs with coils and
external return circular magnetic paths.

see for reference on this idea

http://www.ansoft.com/workshops/altpoweree/Andy_Hirzel_Light_Engrg.pdf


This is the optimal arrangement, spinning central hub with a static coil
arrangement on either side each with thier high mu magnetic paths.

Paul

kewl stuff these hubless rotors!

 

[Mandy]

That's interesting (linked PDF). Not completely sure I understand the stator shift: is this another way of voltage clipping, but
through mechanical means instead of electronics? Also, how does the 2:3 ratio of Mags to Coils affect cogging and output vs. the
4:3 in my original post?

Is it better to have 2 stators (coils) and 1 rotor (mags) or 2 rotors (mags) and 1 stator (coils)? 2 stators is certainly less
expensive! The plans I've been considering had 1 stator between 2 rotors, and there is some danger in assembly of crushing my
delicate digits... nobody wants that . The other way I could see improved safety, but at what performance cost? I'd also lose
the MacGyver factor of using a Volvo strut assembly!

 

[Paul Victor Birke]

That's interesting (linked PDF). Not completely sure I understand the stator shift: is this another way of voltage clipping, but
through mechanical means instead of electronics? Also, how does the 2:3 ratio of Mags to Coils affect cogging and output vs. the
4:3 in my original post?

I would say keep the 4:3 but I am no expert here talking more
therectical. If you also shift the stator coils in my design slightly
the clogging would be even less. By this I mean increment up some
degree shift on one side and increment down on the other.

Is it better to have 2 stators (coils) and 1 rotor (mags)

I think this way and so by implication that author. Remember flux does
not really flow, the magnets just change the state of local space to
quote Faraday.

or 2 rotors (mags) and 1 stator (coils)? 2 stators is certainly less

expensive! The plans I've been considering had 1 stator between 2 rotors, and there is some danger in assembly of crushing my
delicate digits... nobody wants that . The other way I could see improved safety, but at what performance cost? I'd also lose
the MacGyver factor of using a Volvo strut assembly!

the Volvo is very good , keep that approach until you must give up.

P

 

[paul v birke]

Not such a good idea - the "axial airgap stator" is an unnecessary
complication. All the inventor has done is removed the backing plates
from the magnet rotors and held them fixed, separated by an airgap.
Since he has also slotted the plate, he has introduced startup cogging
as well. All he has really bought with his idea is a reduction of
rotating mass, at the expense of complexity and startup issues, and
still that could have been done by using a flat (as opposed to slotted)
plate. I also suspect that eddy current losses will increase when
using the stationary plate to complete a magnetic path for the rotating
magnets.

Dear Martin

What you should do there is use some colled rolled transformer steel to
get these losses down

has there been experiments done with and without a back plate?

you can also arrange the magnets and the coils to have a local flux path
so the concept of the back mmf completing plane can be thrown out

Paul

 

[paul v birke]

Not such a good idea - the "axial airgap stator" is an unnecessary
complication. All the inventor has done is removed the backing plates
from the magnet rotors and held them fixed, separated by an airgap.
Since he has also slotted the plate, he has introduced startup cogging
as well. All he has really bought with his idea is a reduction of
rotating mass, at the expense of complexity and startup issues, and
still that could have been done by using a flat (as opposed to slotted)
plate. I also suspect that eddy current losses will increase when
using the stationary plate to complete a magnetic path for the rotating
magnets.

Dear Martin

What you should do there is use some colled rolled transformer steel to
get these losses down

has there been experiments done with and without a back plate?

you can also arrange the magnets and the coils to have a local flux path
so the concept of the back mmf completing plane can be thrown out

Paul