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Forum Index : Windmills : changing FP characteristics with rotor

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herbnz

Senior Member

Joined: 18/02/2007
Location: New Zealand
Posts: 258

Posted: 07:50am 10 Dec 2007

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Hi Another of those thoughts from across the Tasman.
We I think we all know that winding the rotor out means more revs to get more the same output. I always use this to determine the optimium number turns for performance. I only recently realised how much effect is possible when I retuned a unit with capacitors fitted to log the difference with without.
Now if we arrange a system to
1- wind rotor right out at stand stil will drasticly reduce cogging.
2- as we start turning wind rotor right in give max output low revs. Generator would be designed for best performance at low speeds.
3- as the wind increases arrange to gradually wind the rotor out.
2 and 3 I see could be achieved by replacing the spline with a spiral and spring holding the rotor in as drag icreased it would wind out.
1 not to sure how. maybe we could motorise movement and use wireless control could be element controled by MPPT control that we still only have control for.
I am sure if members pool knowledge a arrangement to move the rotor would emerge.

Herb

KiwiJohn
Guru

Joined: 01/12/2005
Location: New Zealand
Posts: 691

Posted: 08:15am 10 Dec 2007

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I have thought about this and never came to a good scheme. I dont think the spring is a great idea as surely keeping the spring compressed would rob power from the system.

How about the rotor shaft can slide in its bearings and we have some low geared electric device to push it? Maybe a battery drill controlled by the MPPT could wind a threaded rod or something? It might be easier to slide the stator back and forth depending upon how much engagement we need at that time.

Tinker

Guru

Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 02:39pm 10 Dec 2007

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Herb, I had to read your message three times to make sure I read what my eyes saw

. Of all the wierd and wonderful ideas, this one could have come right out of my back shed

Have you considered that in 3 above you would unload the wind generator, something that may be detrimental in high winds?
Anyway, I'm new to this F&P stuff but having fitted the new magnet rotor on an 80s stator rewired to 7 phase, there is NO cogging felt when spun by hand that I would worry about. All one needs to do is to electrically remove the load until the output volts reach charging potential and the thing will, IMO, start up turning in a zephyr of wind.
So, why complicate things by expensive spiral spline cutting? BTW, I would have used a simple thread rather than spirals.
Klaus

Klaus

herbnz

Senior Member

Joined: 18/02/2007
Location: New Zealand
Posts: 258

Posted: 05:42pm 13 Dec 2007

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Sorry delay getting back
FP units are rather complex and although following general principles have aditional querks ie satuated magnetic poles initially that demagnetise as the stator mmf builds up until it eguals the rotor mmf. At this point your generator goes off load and runaway occurs.
Winding out the rotor will make this happen sooner no argument but we should not be at this operating point in a well designed unit.
If we increase the generating ability at low speed ie use more turns it will lose eff at higher outputs we will in fact increase load by bringing back to eff operation with in limits.
The idea could incooperate a change over switch to change windings that would allow reseting to allow a step change with a limited variable range in between.
Moving the rotor on FP is widely recognised to adjust badly designed units and packing washers are fitted to lock the rotor, personally I only use it to determine the optimium operating speed. then make alteration to turns / coil
Herb

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