I'm a little confused about how to calculate the inductance of a wire coil. While I thought this would be really clear, what is confusing me is that there seems to be different ways to calculate it. In this question, the result of the inductance formula is dependent on cross sectional area, number of turns, permeability and the length of the coil. For the calculator on EEWeb, the inputs are the diameter (and hence the cross sectional area), the number of turns, permeability and the wire diameter, and the wire diameter, rather than the length of the coil. I'm unclear how the formulas are related or which one to use. My guess is that the 2nd calculation determines the inductance for a coil one meter long and I have to divide by the length of the coil I'd want to find the inductance of, but I'm not sure.
Electrical – Confusion about calculating inductance of a coil
inductanceinductor
Best Answer
No, it's got nothing to do with a 1 metre length of solenoid.
The EEweb calculator is definitely problematic because it assumes all the "turns" are stacked on top of each other and not laid out like a solenoid. This can be easily proven. For instance if I set up the loop diameter to be 279 mm and the wire diameter 1mm, I get an inductance of 1 uH.
If I double the turns I get 4 uH. If I make the turns 100, I get 10 mH - this is exactly how inductance would change if wound on a core with no leakage flux i.e. inductance is proportional to turns squared.
However, 100 turns cannot occupy a close-knit volume of space and at all possibly hope to have 100% coupling from every turn to each other turn.
Basically, it's a pile of doo doo.