Sizing the blades?

[jaskiainen]

Hi all!

My first genny is almost ready. The blades are only thing to do now.

My question is about sizing them for best performance for my generator?

First of all i think you guys need some informations:

Dual rotor (75mm) 12 magnets each. Magnet size 12mm x 3mm.

9 coils 3 phase star wounded stator.

Each coil has 97 strands of AWG#26 wire.

A single coil is .8 ohms so each phase is 2.4 ohms.

I've done a testdrive with my friends lathe.

Open voltage results after rectifiers:

400. rpm 6.9 volts
     
500. rpm 9.8 volts
     
630. rpm 12.8 volts
     
800. rpm 16.6 volts
     
1000. rpm 20.0 volts
      
1250. rpm 25.2 volts
      
      

And hooked to a 12v battery amps are:

630. rpm 2mA
     
800. rpm 400mA
     
1000. rpm 1.7A
      
1250. rpm 2.2A
      
      

I think after what i've heard and read so far i'm going to make the blades

out of wood. Everybody seems to say they would perform the best.

If i have got it right the bigger the prop the higher the output in watts

but it's also much slower than a smaller prop?

I don't mind if the startup speed would be a little greater lets say like 12mph.

If there is someone with great experience with this i would be grateful for

any help.

I hope i gave you enough information for this one.

[Flux]

I hope you have very free running bearings or this is not going to start.

Probably your best bet is about a 3 ft prop with tsr 7. If you have decent well lined up bearings with light grease then it should work well enough.

If you are hoping to get away with plumber blocks or something then no chance.

PVC blades will be too slow to do anything except in a gale but may start better.

With wooden blades you may get away with choosing the pitch angle for tsr7 but increase the chored width for tsr6 to get a better starting torque.

Flux

[jaskiainen]

Hi Flux

Just the man i expected to answer.

My bearings right now are used but i'm gonna change them later to new ones

so i don't think that would be that much of a problem.

My only consern is that i don't quite understand all the meanings of

that?

For example TSR? Tip speed ratio yes, but i don't understand how it affects

to my blades? Does it something to do with the blade angle?

I just ordered Piggots book couple of days ago and i was kinda hoping

that there would be some information of that part?

I can read the carving plans quite well and even understand them but when

it comes to changing them with different TSR values it goes over my head?

If i'm understanding the formula right it will go something like this:

1/2*air density*propel swept area*windspeed cubed

so 1/2*1*(3.14*(0.45*0.45))*(6*6*6)

1/2*1*0.64*216=69 watts

The efficiency of my genny would also affect with this so lets multiply it

with .15 wich gives me 10.4 watts at 6 meters per second wind.

Does this sounds right?

I'm hoping that later on i can understand all the basics better and give

some help here to other newbies.

[Flux]

Not sure which of Hugh's books you are getting. Windpower Workshop does give pitch angles and solidity for various tsr.

If it is one of the construction books for building a turbine then the prop for the 8ft machine is tsr7. Just scale the thing to 3ft.

Old bearings may be better than new ones as they will have freed off with use and if they have rubber seals the nip will have gone.

Yes 10W at 6m's seems sensible.

Flux

[jaskiainen]

Thanks!

I think then i have something to work with.

[wooferhound]

Hey

This should help you out a lot !

Alton's Propeller Carving And Power Calculator

http://www.alton-moore.net/wind_calculations.html

[jaskiainen]

Hi Woofer!

I've already tried that calculator with different values and it seems nice.

I just don't understand all of the terms there?

Stations i get. Station radius i get. Blade angle i get.

But don't know the blade slope? What does that presents?

Chord i get. And drop i don't?

I believe i can carve the blades with the little i know, but how good they will be?