What physical characteristics add capacitance to an air cored inductor?
Presumably there is capacitance between adjacent windings.
Multilayer coils would have very different capacitance than a single layer coil.
A stretched single layer coil is probably different from a close wound single layer coil.
Are there ways to determine these "in coil" capacitances?
What about capacitance to adjacent planes?
Are there ways to minimise this effect?
Presumably there is capacitance between adjacent windings.
Multilayer coils would have very different capacitance than a single layer coil.
A stretched single layer coil is probably different from a close wound single layer coil.
Are there ways to determine these "in coil" capacitances?
What about capacitance to adjacent planes?
Are there ways to minimise this effect?
There is discussion of this on radio websites. One option is to wind the coil in several sections, with some space between them - known as 'pie winding'.
A few weeks ago I was reading a piece (I forget where) which said that coil self-resonance was not caused by inter-winding capacitance as such but by the coil acting as a misterminated transmission line.
A few weeks ago I was reading a piece (I forget where) which said that coil self-resonance was not caused by inter-winding capacitance as such but by the coil acting as a misterminated transmission line.
Essentially the capacitance between turns, combined with an important factor: their distance in the winding order. For example, the elementary capacitance between n12 and n11 or n13 will result in a capacitance Ce/n², but capacitance between n12 and n02 or n22 will have a much larger impact, Ce/(Δn/n)².
Winding techniques that avoid the proximity of "distant" turns reduce the global capacitance: "scramble" winding for example should be avoided.
There are derivations, approximations, nomograms. Look at Tesla coil building sites, they give lots of practical information on the subject.
Yes, winding techniques like honeycomb, segmentation, spiral, cone, "winowed" coils (I don't know the exact english translation), same direction layering instead of alternate, etc.
The coil itself should be as large as possible to minimize the number of turns and their associated capacitance: it is obvious that a single turn 10µH of 1 meter in diameter will have a lower capacitance than 50 turns on 1cm dia. (in a quasi-static perspective anyway). Choosing the optimum form factor will also help a little. The insulating materials also play a role obviously.
So put it in a useful context. I never thought about it before. Assuming something like a crossover, that being where I might most likely use such an inductor, pick a typical value. Then for a typical coil, what amount of capacitance would result, and how would it be represented schematically. Then what effect would it have on a circuit. In other words, if I make a 1000Hz crossover, what would the coil capacitance do to the frequency or the Q or slope or some other parameter. And by careful winding planning, how MUCH could I change this capacitance and thus how much change to expect. And assume reasonable conditions, like a living room speaker size, so no meter diameter coils.
And if crossovers is not the issue, maybe coils in an SMPS or something? I guess capacitance there would be a whole different matter. Or would it?
And if crossovers is not the issue, maybe coils in an SMPS or something? I guess capacitance there would be a whole different matter. Or would it?
It has been said by a few authors that:
All capacitors become inductors at very high frequency
and
All inductors become capacitors at very high frequency.
With those quotes in mind, it seemed to me that any inductor will fail to work at some high frequency and further that the lower the parasitic capacitance, the higher the frequency at which the inductor will still behave as an inductor.
It seems there are ways to minimise the capacitance and that these methods will allow inductors, for any duty, to behave as inductors over a wider frequency range, than if we haphazardly wind then any which way.
All capacitors become inductors at very high frequency
and
All inductors become capacitors at very high frequency.
With those quotes in mind, it seemed to me that any inductor will fail to work at some high frequency and further that the lower the parasitic capacitance, the higher the frequency at which the inductor will still behave as an inductor.
It seems there are ways to minimise the capacitance and that these methods will allow inductors, for any duty, to behave as inductors over a wider frequency range, than if we haphazardly wind then any which way.
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