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Lamp Man

Newbie

Joined: 27/11/2009
Location: Australia
Posts: 1

Posted: 01:06pm 21 Dec 2010

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Hi all
I have just finish a mill with a f & p smart drive with 6 blades pvc type dia 2.4 m
I have tried 4 or 5 stator configurations and still not getting much output, my main problem is not enough height and too many trees I am up 8m now and working on another 6 m
So back to the magnetic rotor, I need an alternator, which works at low speed like a 100 rpm or less with no cogging. I have been looking at the Hugh Piggott type alternators with NO iron in the windings. I have a good mechanical and electrical knowledge and a small scale engineering workshop, If you had said twelve month ago rotors will work with NO iron I would have said you are mad,
These alternators consist of a car front wheel-bearing hub with two Steel plates fixed to it and magnet glued to them. What is worrying me is the steel plates are robbing most of the flux of the magnets. So how to improve it, one idea I have is to use aluminium plates with steel pole shoes just big enough to cover the pole winding. Does any one else think this might be more efficient.

Thanks John

Cornelius

Newbie

Joined: 26/12/2008
Location: Norway
Posts: 27

Posted: 01:17pm 21 Dec 2010

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You have it the wrong way around; the two steel plates Concentrates the magnetic flux.

Consider two magnets side by side mounted on a steel plate; one with the north pole on the plate and the other one with the south pole on the plate. What happens is that the magnetic flux follows the plate from one magnet to the other and thus, amplifying the flux in the poles on the magnets opposite the plate.

I think you will have a very hard time improving this design when it comes to magnetic flux.

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 01:22pm 21 Dec 2010

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Hi Lamp man

The steel backing plates provide a magnetic circuit for the lines of force to interact with the opposite poles in pairs around the plate and increase the magnetic efficiency of the rotor, if you use alloy it doesn't conduct the lines of force and will drastically reduce the efficiency of the magnetic rotor.

Al the best

Bob

Foolin Around

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 01:29pm 21 Dec 2010

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Hi lamp man,

[quote]Does any one else think this might be more efficient. [/quote]

No its a bad idea.

The steel dont rob the magnetic power, it gives a magnetic flux return path.

You might consider it a bit like only using the positive terminal on a battery....nothing will work until you give a return path to negative terminal.

With a AXFX generator you NEED the steel plates, and the steel plates should be close to the thickness of the magnets.
If the steel is too thin then you will get flux leaking through the plates.

Not sure what you mean by this "with steel pole shoes just big enough to cover the pole winding"

This would imply you are looking to place steel back in the coils, which is where you dont want it.

Do you realize by having 6 blades you present mill will spin slower than if you only had 3 blades.
Although the torque will be less but the rpm will be higher.

Mills and generators are a fickle thing to get the combination right to suit the design.

Have you got some photos for us to see your mill.

Pete.

Sometimes it just works

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