Hugh Piggott 4 FT. modification ideas

[pgitta]

I have built the 4 foot turbine for practice in constructing the larger versions. I purchased plenty of 15AWG wire for the larger size, and since the smaller machine calls for 16AWG, rather than shell out the cash for a size that I would only use for the small experiment, I used the 15AWG and made coils exactly to specs for the 8 FT. machine.

Instead of fusing the stator to the pipe, I chose instead to fabricate a sort of static spinner on my wood lathe that has about a 5" diameter on the inside end which I screwed the stator to with stainless screws. This way I can just slide the stator onto the pipe and using set screws in the spinner, adjust the air gap that way. It also allows me to tweak the stator square to the rotor.

I made the rotor with N42 magnets, stronger than called for in the plans.

Anyway, I'm still getting pretty close to the called for output, though I have to back off the stator because of the larger coils and stronger magnets to allow the blades to spin up.

What I'd like to do is add a plate without magnets to the front of the stator to increase the field strength. I already know I need a larger diameter swept area as it is, but my question is:

What would your reccomendation be as to final swept area diameter assuming:

N42 magnets

8 ft. machine size coils @ 85T, 15AWG (1/2 in. finished thickness)

1/8 in. steel magnetless plate flush with front of stator.

I was speculating around 5.5 to 6 ft. range.

What do you experts think?

[Flux]

5ft 6" ( 5.5ft)  would seem reasonable.

If you go to 6ft you will need to use a higher tsr for the prop. At 5.5ft you can leave at about tsr5.

You will need to spin the disc in front of the stator, you can't leave it stationary, you will have to work out how to do that.

Remember you will need to increase alternator offset and tail size or length to suit the larger prop. ( another reason not to go up to 6ft).

I did one like that for a poor wind area with 5.5ft prop and it works extremely well with N40 metric magnets. I built the hub from scratch, you may have trouble with lack of space at the centre of the stator but I am not sure what you have done.

Flux

[pgitta]

Hmmm... I assumed the plate could remain stationary. Guess I don't understand why it would need to spin if it is uniform across its width in every direction.

Thanks for the reply. Spinning it opens a whole new can-o-worms.

[Flux]

If you don't spin it you will have terrible eddy current losses in it. You would need high grade laminated strip steel or something to leave it stationary and even then it may not be too good.

I suspect you will need a larger disc attached to the prop on the outside and spaced off by some means if you have followed the original construction, I don't see how you can drive it from the centre.

Flux

[tecker]

I think it would be worth your time useing thin steel as hidensity as you can get for stator backing  to a single rotor until you can get the money for some more mags .  Run some tests and post your results .