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Re: [TCML] Dr. Resonance inductors - 1/16th of an inch?



Hi Stephen

Can you tell me where that formula came from? I had not seen that one before. Also you say d is coil diameter in inches, is that mean diameter or total diameter?

later
deano

On Friday 06 March 2009 03:02:00 am Stephen Hiscock wrote:

I believe inductance is calculated by
L= (d2 * n2)/(18*d+40*l)  (MicroHenries)
where:
L is inductance in micro Henrys,
d is coil diameter in inches,
l  is coil length in inches, and
n is number of turns.

That's ONE of the several Wheeler approximations for a single-layer solenoid, far far from the optimum shape for a relatively low frequency high inductance inductor. I have a University of Illinois research bulletin which derives the optimum shape for an air-core power inductor. Can't find it right now but as I recall the coil cross section is square and the ratio of outer to inner diameter is 4/3. Lots of design equations and tables of measurements in it - wish I could figure out where I put it.

Remember that the objective here was an inductor capable of carrying about 1 amp - #30 wire just wouldn't hack it.

Ed

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