Packing in more copper and other things

[angus]

G/day and Hi Y/all.  top of the season to all.

Just some thoughts.

For an AF turbine we need to try and pack as much copper wire into a given space (per coil) as possible.

In my trade (steel fabrication/welding) I have used both "Layer wound" and "Random wound" Mig wire reels. Both reels have 15Kg of wire wound on them ,however the layer wound reel is about 2/3rds of the diameter of the random wound one - that is it is 2/3rds the size.

Layer wound is where each layer of wire - as it is wound - is seated in the grouve of the adjacent wires of the previous layer.

Random wound is where the wires wind randomly over each other as the layers are formed.

 Perhaps layer winding is the way to pack more wire into the coils?

As an aside-

It is known that the circle will enclose the maximum (cross sectional ie. less resistance) area for a given perimeter-and hence the use of circular wire.

The next best is the square cross section.

What if - instead  of useing say- 1.8mm round wire - we used 1.8mm square wire.

The volume taken up  by a given number of turns would be the same for both- ie. the coil size would be the same , however the square wired coil would have a lot more copper.

All this is subject to the price and availability of square magnetic wire.

Finally a silly one to round off the new year.

The weight of the 2 rotors (ie steel plates and magnets) is far more than the weight of the stator.  If we could make the stator strong enough -(a big ask)-

why not spin the stator (ie it is now the rotor) and fix the 2 rotors (ie they now become the stator).Gyro forces on the now-rotating stator would need to be considered.There would ,however be far less mass to accelerate and decelerate and these gyro forces would be a lot less as the mill hunts around for the wind.

Regards

Angus (The older I get , the better I was!)

[TomW]

So, if you spin the stator don't you think the compexity of picking off the power will offset your envisioned savings in rotating mass?

Maybe I don't understand your proposal? It is early yet.

Tom

[freejuice]

I'm a rookie in all of this...still trying to get a tower up and going.

I guess it could be done, but you would need some sort of slip ring to transfer the current to your cable.

Since I'm still trying to get a grasp on things, I see the starting torque of the mill being governed by the resistance in the cables/battery arraignment more so than in the rotors. For example, the 10 ft machine I have will spin very freely in a slight wind, but once everything is hooked up under a load and experimenting with producing power, it is a different beast....If I follow the Dan's and Hugh's advice, I'm sure it would be quickly straightened out.

It appears to me that the rotors dont hardly affect the start up speed since they are so close to the center of rotation and spin so freely; if everything else is good to go.

Another angle to look at would be how much momentum the steel rotors provide, especially when the wind is up and down the scale on windy days...would the other system, have many more startup's or loose rpm's quicker?

 Just throwing out random thoughts in all of this, not an expert by any means )

Many more folks in here have vastly more knowledge than me.

 All the best,

 Gavin

[wooferhound]

I think I saw a story here one time, where the guy wanted to spin the stator one way and spin the magnets the other way.

[joestue]

The general figure is random wound coils pack about 56% copper fill.

Layer wound coils with stiff paper insulation is π/4, or 76%, once they are nested its 90.7%.

This neglects the  lost turn every other layer, a 100 turn coil will have an additional 5% in volume. Add in the insulation, say its 5% insulation 95% copper, and you are down to 81% copper fill.

I don't see why a mass produced stator wouldn't be built using copper strap, 90% fill is easy, thicker copper makes 95 and 97% attainable but prohibitive due to the required number of turns.

DIY with epoxy impregnated craft paper and 10mill copper, 90turns per inch of coil width seems reasonable to me.

I haven't seen any turbines here that are random wound.

The rotational inertia of the alternator is negligible IMHO.

[Flux]

With extreme care you can get a few more turns in compared with an average quality quick winding.If you have no other ambition in life than wind perfect coils you may get a very minor improvement.

Square or rectangular section does give a better stacking factor but the availability and cost of wire makes it a non starter unless you are very lucky. You are limited to quite small sections to avoid eddy loss and once you start trying to wind several strands in hand you will struggle to not loose space. if it is high voltage and you can get the square wire and do it with a single strand then go for it if the cost is right. Probably costs far less to use bigger magnets and a less careful winding in most cases.

Copper tape looks attractive at first sight but is not without its snags either. Large rectangular strip has way too much eddy loss.

Spinning the windings and having slip rings is crazy you are making trouble.

I consider the constant worry about rotating mass to be another unfounded fear. If you can reduce mass that you need to get in the air then that may be a good idea but I don't consider rotating mass as such to be an issue. Some of the older heavy ferrite magnet alternators perform very well and usually survive better than light weight things. The inertia of the blades will be greater than the alternator.

Flux

[Perry1]

I don't think that rotational mass is that big of a deal. Big steel plates at the hub add as much 'rotational mass' as 3 quarters taped to the tip of your blade.

Also, as far as momentum is concerned, this is another misnomer. It takes wind energy to overcome this momentum so more energy to spin it up, then it holds the energy as rotational momentum. So there is no net effect. If you are counting on rotational momentum then you are already in low winds and way under cut-in speed.

In regards to spinning the stator. Sounds Rube Goldberg.

Perry

[taylorp035]

I remember that too!

I would think gearing it up 2:1 would be easier than making a contra-rotating motor.  They do make large contra-rotating brushless rc helicopter motors, some up to 2400 watts.

Lets just hope no one tries spinning the blades in opposite directions!!