Calculated coil turns

[jaskiainen]

Hi!

I'm about to start soon my next generator. Already have got magnets.

They are 30mm dia 10mm thick grade N45.

16 poles dual rotor, 12 coils, three phase system.

I calculated the rounds/coil with two different formulaes and got

quite a bit different results.

First i used Hugh's formula.

Turns per phase = 17000 x (System voltage V +1.4) / ( Desired cut in speed RPM) / (Strength of flux in Tesla) /

(total area of magnet face in square inches) = 17000 x 13.4 / 200 / 0.6 / 17.53 = 108 turns per phase.

If you have twelve coils total and thus 4 per phase then you should have 27 turns per coil.

Second i used some other foprmula wich i came across in fieldlines.

N =  E / ((B * AM) / P)

N = 13.2/((0.6*0.000706858)0.3) = 13.2/0.001413716 = 9337

Where,

N = Total number of turns (for all coils)

E = Voltage generated at cut in speed (13.2)

B = Magnetic flux in teslas ( 1 tesla = 12,000 guass)

AM = Area of the Magnetic Pole in square meters

P = Period (the time it takes the turbine to complete one rotation)

Using the above formula, 9337 turns of wire are needed.  

In the calculations, 0.6 tesla was used for the magnetic field.  

Since I have 16 poles and 12 coils, I determined 48 turns are needed per coil.  

The turns per coil was found by dividing the total number of turns by the product of the coils and poles.

The formula for this calculation is as follows:

TC = N(P * C)

Where,

TC = Turns per coil

N = Total number of turns (9337)

P = total number of poles (16)

C = Total number of coils (12)

So wich one goes nearer?

If I have to guess, I would say 27 turns per coil might be closer the truth.

I will built the magnet rotors first and then make a test coil to get the cut in

speed around 200 rpm. So these calculations are kind of useless to me anyway.

It would just be interesting to see wich one comes closer.

I thoght that this time i built the rotors and stator first and test it with

lathe. After that i can decide the blade size. I'm still just guessing here but

i am thinkin of seven footer right now.

[Flux]

I am too lazy to check formulae but by approximating to a magnet 30mm square. with 600mT and 27 turns per coil I got a cut in of 165 rpm assuming it is 12v.If I take a nominal 14v then I get about 187 rpm.

I think you can safely assume Hugh's formula is correct. I can't be bothered to check the other one, it may still be correct but the units may be different, it might be in Gauss or something.

There will most likely be more error in choosing your flux density than any other factor so a test coil is a good idea but start with the results from Hugh's formula and you will be near enough.

Flux

[Flux]

I have just had a quick look at your second formula and I see one obvious mistake. 1T is 10kgauss not 12.  12kg is roughly the remenence for neo.

Without going deeply into this I see no factors for star connection or the factor for a 3 phase rectifier.

I suspect it is a single phase equation with an error if you copied it correctly.

Flux

[jaskiainen]

That might be right. I'm not sure if it is for a single phase system.

Anyway my goal is 3 phase system so i stick with hughs formula.

Maybe i start my testcoil with 35 turns and then reduce it one round at a time.

I know i should use as thick wire as possibly can squeeze in, but i don't want

to do bigger than 8 foot dia rotor. Hope i can come out with seven footer.

I have calculated the available power out for 7 footer and it is about 500W

in 10m/s wind with coefficent 0.3.

With TSR 7 it will be around 636 rpm in 500W.

Ok, i don't want to harvest 500W in 10m/s with 7 footer. Let's say 300-400W.

What size wire would carry that much? is AWG15 or AWG16 enough?

We have AWG20 at work a whole 12kg reel. I might get some of it quite cheap.

Or is it better to use the thickest possibly wire in stator and open the airgap

for my purpose? Afterwards if i need it a bit bigger i can make another set

of blades and close the airgap again?

Just some things that have crossed my mind lately quite often.

[Flux]

 I can't really deal with the round magnets but using the 30mm square x 10m thick I come up with about 24 turns in a stator about 1/2" thick. Assuming a magnet rotor of about 14" diameter.

If you use a smaller rotor diameter it will restrict your space for thick wire. With the 14" discs I would expect you to get in 10 gauge. That is too thick so you will need several strands in hand.

The only way to use #20 would be to wind the coils with 4 times the number of turns and Jerry connect it with a rectifier for each coil. I cant imagine you could wind a bundle of wires in hand unless you twisted them together first to make a sort of litz wire.

On my findings it would stall hard with a 7 ft prop. Firstly open the gap to the maximum you can stand without loosing low speed performance then add resistance to get it on song at about 20mph. It should be pretty bomb proof and 400W should be fine but furl above that.

If you settle for a smaller magnet disc then you may not need series resistance but you will have to keep to below 300W.

Try to use all the available winding space or nearly so.

Flux

[jaskiainen]

I have already made plans for 10.5" rotor discs.

It gives me space for single coil 31mm ID and 60mm OD.

That seems plenty to me. If i use AWG14 i can get single strand in with only

3mm thick coils. So maybe if i use two in hand AWG14 it could do ok for me.

I don't want it to stall badly and i don't want to lose any of slow wind speed

performance wich is most of the time in here.

I don't know what the max power out it would be with that without burning

the stator, but i hope someone could give me a rough estimate on that.

I know that most of the people here suggest to built something thats done before

and proven to work, but i like to do things from the scratch. It's live and learn

to me. Also i hope that people here would use plenty of different size and shape

magnets to built their own generators. This would help the others in here.

[jaskiainen]

What the heck did i say there?

With single strand of AWG14 the stator would come out like 6mm or 1/4 inch.

With 2mm airgap on both sides the magnet rotors come just 10mm apart.

That is exatly thickness of one magnet.

So how much can i expect with only single starnd of AWG14 from it without

pushing it too far and burn it? Or should i try to make stator a bit thicker

with multiple wires?

[Flux]

I suspect you will hit 50% efficiency at about 300W with #14 wire. If you can get it to furl very precisely at 300W then it will probably be ok. It should not stall so once you have got it furling to the point where it reduced power below 300W in high winds it should be safe.

If you want to try for thicker wire I suspect you can squeeze the coils elliptical a fair bit and not loose much in terms of volts. Raising the magnet gap to 12mm and perhaps adding a few turns may get you 2 strands in with care. This will then let you run up to about 500W but unless you have a lot of line resistance or add some it will stall.

If it is a low wind area and you can make it furl then the single #14 should do what you want.

Flux

[jaskiainen]

Almost anything can still be done. All I have right now is magnets. I just visited

a car wrecker yesterday (what is that yard wheres piles of car wrecks all around? Just can't remember that word right now) and he promised to look suitable hub for my generator. After i get that hub i know exactly the magnetrotor size.

I still can make them a little bit larger to get little bit more space between magnets. That would allow me to use some heavier wire or two in hand AWG14.

Nothing is sure right now but the magnets i'm gonna use on this one. Also this time i'm gonna take a lot of pictures to share in here. If the camera is not with me then i shouldn't do a thing.

And thanks a lot Flux, You've been a big help. Again.