Scaling down the Otherpower 10' generator

[Newport Woody]

I eventually want to build the larger 10' model on the otherpower site, but I want to start with a small one to get the hang of it.  I bought 24 -  1" X 1/2" X 1/4" NbFeB magnets and am building a dual rotor altenator.  6" O.D. disks 12 magnest each with similar layout as the 10' dual rotor.  The stator will have 9 coils wired in 3phase.  Not sure how heavy to wind the coils or how large of blades I should attempt to carve.  I know the blades have to be matched to the alternator, but after reading the posts here it seems more complicated than my ability to figure out.  I know it depends on the desired voltage, TSR desired cut-in  etc etc.

My main objective is to learn from this thing, I'll find an appropriate use for the power once I see what it puts out.  Winds are frequently between 10 and 20mph here. If someone could recommend a good voltage to target (12V, 24V, 48V), blade diameter and lbs of wire in the coils it would help.

[Flux]

This is mostly going to be a toy. OK if you only want to learn.It's going to be rather less effective than Hugh's little 4 ft machine and a lot faster to get similar results.

I wouldn't want to use more than a 4ft prop on it.

I think you had better choose your voltage on the basis of the larger machine. This is going to be tiny and there would be no logic to choosing other than 12v but don't let that settle your final voltage. 12v is not so clever for 10ft but just about possible if you want hard work.

For 24v you are going to want something like 200 turns so thin wire and stator not much over 5/16" thick. You can scale Dan's prop for no more than 4ft. You can scale the offset for 4ft but furling tail weight may not work out even in the right league.

I would be tempted to base a lot of it on Hugh's 4ft but you will need a faster prop and it will have to furl earlier.

The prop scales ok. Things like offset scale ok but magnets don't scale with linear dimensions.

Flux

[TheCasualTraveler]

Just a thought,

     Seems to me there is a simple way to get more out of this thing. Change the steel magnet discs to 8", and then, as Finnsawyer recommended to me once, use the same magnets but turn them sideways. Wire would probably need to be #24 or smaller. Or leave the magnets the normal way but on 8" discs and it would give you about 1/2 inch for coil legs.

Just a thought...

[Flux]

Just accept it is a toy for learning and you won't be disappointed. It will do better with bigger discs but it is not going to be spectacular. It's really a 3ft machine but you can push it to 4ft and make a better toy.

Flux

[Newport Woody]

Understand it will not produce real usable power.  My 9 year old is working on this one with me.  I figured I would get around 10 watts out of it and connect it (through bridge rectifiers) to a old car battery.  He wants to use it to charge his handheld video game, and get credit for science fair.  So I will go with 12V.

So I'll start with 100turns, do you have an idea of what speed to test the test coil at?

Do you think I'll need a dump load controller or since its so low wattage it will disipate as heat in the battery?  For starters I'll try Dan's design at 4'.  And make the tail lighter(?) to furl earlier.

[Flux]

Try 300 - 350 rpm cut in.

If it's a big battery and you use a fair bit of the power you may manage without a regulator. If it's an old battery you probably won't shorten its life much, don't let the water get low.

Good learning experience for your son.

Flux

[Newport Woody]

I have a question about coil shape vs. magnet size/shape.  If looking at the top coil.  Do you want the coil length/height to be larger than the magnet length/height, i.e the magnet does not pass through the horizontal bottom and top of the winding?  Also does it matter how wide the coil is?  Can it be infinately wide as long as a north pole enters one leg at the same time a south pole enters the other?  Does coil leg width matter?  Should it be the same width as the magnet or 1/2 or 1/4?

The reason I'm asking is the only hub I can find is proportionaly larger forcing the magnet circles diameter larger making them farther apart. (8" vs 6")  Therefore my coils are getting shorter and wider.