So while reading up on air-core inductors I encountered three formulae for calculating the inductance of cylindrical inductors.
d^2 * n^2 d = Diameter (in) L = --------- n = Turns 18d + 40l l = length (in)
The coil I made last night was built on the basis of this function. d = 1.15; l = 1.375; n = 24 which gives ~10uH
Then, Wikipedia:
d^2 * n^2 L = --------- 9d + 10l
With this function the calculation results in 31.6uH.
At
Eventually I located this:
Which for my inductor gives 9.45uH.
That's four (two, depending on how you count) different results from several equations. Who's correct? It's all too common to read a wikipedia article and assume it is more or less correct, but these results are not encouraging for several reasons.
I don't know what a factor of 3 difference in inductance will mean to a buck-converter circuit, but I suspect it is much more critical to oscillators in RF circuits. I'm inclined to suspect the first formula is correct since it closely matches the one directly above, but I have no way of being sure about it.
In short, this sucks.
Regards,
Uncle Steve