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