Calculating a single layer air short coil

Thread Starter

PaulEngineer

Joined Dec 21, 2016
217
Hey all. Good day to all of you :)

So, i wanted to ask, how to calculate an air coils. I found this formula (but i dont really know, is it the right formula?):

L=μr*μo*N^2*r^2/(xD+xr). x= any number f.e. L=μr*μo*N^2*r^2/(9D+10r). Can you help me to find the solution on my problem on how to calculate the coils? Because i became totaly confused. I dont even know for real the exact formula/s for its calculation.

Thanks
 

Thread Starter

PaulEngineer

Joined Dec 21, 2016
217
So, if i understood well, the formula of single layer air core coil is the following:

L=r^2*N^2/(9r+10l)?



P.S. I have another question. The (9r+10l) of the formula could have different numbers f.e. i will write something in luck (120r+228l) or (18r+90l) or whatever, (i dont know anything about this formula. Maybe there are specific numbers.) So anyways. Are this numbers (Xr+Yl) specific for each type of coils? Or the (Xr+Yl) can take every number for X and Y values? So if i understood well, the "in formula" (9r+10l) is about single layer air core coil, i dont know if im right. I just need to understand only this thing.

Thank you very much for your posts, they are always helpful for me. (The Coil32 is good calculator? I have the app)

PaulEngineer
 

AlbertHall

Joined Jun 4, 2014
12,345
AFAIK all the formulae for coil inductance are approximations often derived from finding a formula to fit experimental results. The formula that works well for a long thin coil won't work so well for a short large diameter coil.
 

OBW0549

Joined Mar 2, 2015
3,566
So, if i understood well, the formula of single layer air core coil is the following:

L=r^2*N^2/(9r+10l)?
Correct.

In that formula, r is the radius of your coil, in inches. N is the number of turns in your coil. And l is the length of the coil, again in inches. Plug those three numbers into the formula, and the result is the coil's inductance in microhenries.

It's as simple as that. From the length and radius of the coil, and the number of turns, the formula gives you a close approximation (allegedly within 1%, according to the reference I posted) for the inductance.
 
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