Need some help with calculate tesla for my coils

[jaskiainen]

Hi all

My first genny is starting to come to a point where I'm about to wind my coils.

I will tell you the basic things right here at start:

12. volts system
    
12. round magnets 12mm(0.472440 in)* 3mm(0.118110 in) N52 (1,48 Tesla)
    
9. coils, airgap should come around 5mm (0.196850 in)
   
   

Startup speed should come around 300rpm. (Am I aiming too low?)

Prop will be around 75cm (2,5feet)

Coils have limited space id 12mm od 21mm and thickness around 4mm so im trying to

calculate here with different wire gauges to see what I can fit in that space.

(I'm thinking gauges between 26-30, I did wind one with #31 2 in hand and got 85 rounds to fit in it

only problem with that is the high resistance of the coil: 1,5 ohms for a single coil)

This is the time when I say again: Yes I know it's not that wise to built up this

size generator, but then again who ever said I'm that much of a Einstein?

I know the formula to calculate the coil windings, you can find it in here:

http://greenbits.com/Formulas/Coil+Turns

But I need some help with that "strenght of flux in tesla" part.

All I can do right now is guessing and I just don't like doing that because its

effecting quite much to my coil turns

Here I hope is all the information what you need to tell me the flux.

Any suggestions are also wellcome

[Flux]

Assume 700mT and try a test coil to see how near you are.

Flux

[jaskiainen]

Thanks Flux!

Funny that I did calculate with .7T before, but then I just start to think that

if the magnets physical size would effect much for the result so it would be much

less than that.

Ok. This clears things up for me I hope.

Oh, one thing that I forgot.

How much the coil resistance would effect to my stator?

Would it perform a heat? Or just kill the output for my genny? Or both?

[Flux]

I have just looked again and I see that you say you have 12 magnets.

Sorry I assumed it was dual rotor 12 pole with 9 coils.

If it is single rotor with a spinning disc then you will be down to nearer 450mT.

If it is single rotor with no return path then I don't know what you mean by air gap and I think you will struggle to get anything worthwhile out of it.

I won't reply to your bit about resistance until we have sorted the magnets out.

Flux

[JW]

you shound have 24 magnets. Not just 12. I can help but questioning the decimal place, should it be .07T (tesla's ?) 'im assuming(ouch)' at 450mT that in the best possible case there's goning to be some loss in the magnetic circuit otherwise 350mT would have been specified.

Does that have anything to do with 'air-gap'

JW

[jaskiainen]

My mistake!

Even if I double checked the post.

Yes this is dual rotor 24 magnets 9 coils system.

[Flux]

OK glad we sorted that.

At 1.5 ohms per coil you are a bit high but it should work.

I agree with your 80 or so turns but as I have no idea of the disc size I can't guess what wire you can get in. Try squeezing the coils into a bit of an egg shape to gain a bit more leg room. Don't cut the radial dimension but squash them a bit so the hole is only perhaps 9mm wide but still 12 high. If you can get down to 1 ohm per coil it will be better.

I doubt that such a small machine will burn out even without furling as the total watts lost in it will be small ( though large in relation to output). The prop will probably become inefficient (and noisy) enough to protect it in high winds. Furling would be better if you want some practice for your next machine.

I assume you are aiming for a prop tsr of about 6.

Flux