Coil dimensions

so i have been drawing up my coil setup and i realized that i am missing some important information. if i wind 2 strands of #14 wire 35 turns as seems to be very popular for 12 volt systems what is the thickness of the wire part of the coil? roughly if fine. i hope this makes sense. what i need to do if fit the coil so that it will match up with my 12" rotors so if i know how wide each side of the coil is then i can make the center hole of the coil small or large enough so the OD of the coil will fit in the allowed area. so if i make my center hole of the coil 1/2" x 1" then how large will the whole coil be?

Thanks
~DK

Hi DK,

Heres my thoughts: The actual thickness of your coils will be determined by your winding fixture. For me, it is important to make the coils just a bit thinner than final thickness of the stator out of the mold. This way, the mold is sure to close when you get some glass cloth packed with resin. So, the "form" that the coils are wound around is about 1/32"- 1/16" thinner that the mold cavity depth.

The inside shape of the coil should be consistent with your magnet shape and path. The outside shape doesnt matter as long as all of your coils will fit in a circle along the magnet path. With that in mind, play with a test coil and adjust the "form" of your fixture if needed to make sure all the coils fit properly when the stator is complete.

Heres a nice "coil winding" video on youtube.

http://www.youtube.com/watch?v=bseit46ezOo

Not sure if Ive made much sense...but I hope it helps.

-Rob

so if i were to use 1" x 2" x 1/2" magnets i would want my center hole of the coil to be about 1" correct and the top just a bit larger. i want my coils to work with a 1/2 thick stator and the rotors to be 12" diameter with 16 magnets of each one. so i need 12 coils to work in 3 phase all positioned so that the magnets pass over the longer portions of the coils perpendicularly. i am just worried that my coils will not fit. would making the center hole of the coils just a bit smaller than the magnet face be a big issue say i made it 3/4" on the bottom and more like 1" on top with the same 2" x 1" x 1/2" magnets.

if my form is made to allow a 1" x 2" center hole how large will the entire coil be? roughly.

Thanks
~DK

wow thanks a million that was great. i realize the only way to be sure is to wind one and check but i dont plan on winding this thing for a while and it is one of those things that i cant stop thinking about and it really bugs me. that is good though it shows i am psyched about this. it looks like i should be ok.

thanks a million
~DK

Ive got some info that might be helpful. I took some info from a known coil. It was wound with 60 turns of 2 x 18 ga.



I measured the cross section and came up with an area of .480" x .625" = .3 sq inches.


Then I calculated the cross sectional area of just the conductors 120 x 18ga(.043 diameter) = .174 sq inches.

From here we have a ratio of the coil section -vs- the solid conductor section ~ 300/174 ~ 1.7

This number may tell you that your coil cross section will be about 1.7 times bigger than the solid conductor equivalent.

For your coil, figure the cross section of 70 strands of #14...then multiply it by 1.7 ...and that is an approximation of your coils section. Divide this number by the 1/2" for thickness and youll get your width of your cross section.

Cut out some cardboard models and see how they fit.

Another note on your coil shape: In the radial direction, if your magnets are 2" long, I would make the inside (air-core) of your coils about 2-1/4" to 2-3/8". Then make the arc width of the inside shape...so that all of the coils fit together like slices of pie.

You can play with sketches...but eventually, you just need to wind one up, check it, unwind it, adjust..repeat.

-Rob