Stator Coils

[WillyJo]

I am a high school senior working on an engineering project.  I am building the 10ft diameter wind turbine that is detailed on otherpower.com.  I received a donation of 9.5 of 15 AWG magnet wire.  On the site it shows how the number of turns for different gauges of wire results in different voltage outputs, however it doesn't seem to show for 15 gauge wire.  I was wondering if there was a way to determine how many turns for each coil need to produce a certain amount of voltage for 15 AWG?

[electrondady1]

there are those, (flux) that can probably tell you that,  ))

  can't remember, maybe Danb uses 14 gauge.?
you could use the same number of turns and get the same voltage at the same rpm with 15 gauge.
but
it will have greater resistance and  won't handle the same amps.
in order to keep the same outside foot print of the original coil and keep the same relationship to the mags you would need to make the coil jig thinner

making the coils , and  stator thinner would allow the mags in closer together

oh boy!
 now we have higher flux density.

when you do a test coil you don't need to cut the wire off the spool .
you can just scrape a length  clean and use an alligator clip to the meter
that way  you can adjust the turn count just seal up the scraped section.





 

[Flux]

I don't have Dan's winding spec handy but besically the thing that affects cut in voltage is air gap  ( distance between magnets) and number of turns, What electrondady has told you is correct. If you are within one wire size of Dan's specified wire it will probably work ok. If the wire is a little thinner it will just mean you have to furl a bit earlier to deal with the reduced current capacity.

If the wire is significantly smaller then you will do better winding on a thinner former and closing the air gap, this will let you use less turns and keep resistance down a bit. It does all interact so you will need a test coil.

Remember that if Dan has specified 2 wires in hand you can use a single wire 3 numbers lower. Your 9.5 would directly replace 12, two in hand. You should be able to find some combinatiom that will work for one of your sizes. You will have even more options if you have a choice of operating voltage. 12v will likely be the most difficult one to satisfy.

If you have to use thicker wire than specified you will have to use a thicker former to get it in and so will have to increase the air gap to get it to fit. This will drop the gap flux and you will need more turns and it all interacts so you can't get away with grossly over sized wire but you should be able to go a number either way without a lot of change in performance.

Flux

[WillyJo]

Thanks so much!  I really appreciate all the input.

Sorry about the confusion, but what I meant to write was that I received a donation of a 9.5 pound spool of 15 AWG magnet wire.

I understand the concept of air gap and flux density.  However I am confused about testing the coils.  I assume I am testing resistance but what resistance am I looking for on each coil?  Can I just use the target resistance to find the number of feet of wire that equates to that resistance, and then wind the coil until that length is consumed?

I don't know what voltage output I am looking for.  I hope to sell the wind turbine at the end of the school year.  What voltage output would be the most likely to sell?  Am I tied down to a certain voltage with the 15 AWG magnet wire?

[Flux]

I don't have Dan's book and the Otherpower web site seems to be being updatede at present so I can't get at the basic Otherpower 10ft details.

The thing with the coils is getting the number of turns right for correct cut in at your chosen battery voltage. Set up your magnet rotors and try a test coil of a size that will fit in the final layout. Pick a number of turns using the otherpower instructions as a guide ( nearest specified wire size). Run the machine at known speed. Bearing in mind that your coil is 1/3 of one phase you can work out what voltage the winding would give with those coils at cut in speed ( 150rpm ish).

You can then scale the numnber of turns to suit what you need for chosen battery voltage.

Remember that the ac volts you measure is 1/3 of a phase, so measure the coil, multiply its volts by 3 to get phase voltage. Then multiply by 1.7 to get line voltage and then by 1.4 to get mean dc voltage. If you are turning it at 150 rpm then this should equal battery voltage. If not you have to include the speed scaling factor.

You can do the test coil with any size of wire, but if you use your  #15 you will be sure thast your coils will fit.

I suggest you start with a test coil about 1/2" thick or a little less so that when moulded it will give a 1/2" thick stator. Try your magnet rotors about 3/4" apart and if your coil comes near you can play with the magnet gap a bit either way.

The main thing is correct cut in, take the resistance as it comes, it will determine stator heating but if you get fully wound coils in a sdtator 1/2" thick with near enough cut in it will be ok.

If you can post the otherpower winding details for various voltages and wire size I may be able to help a bit more.

Flux