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Re: Tesla Coil Formula



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Jared,

You are correct, it is a matter of perspective.

The magnetic field in a short solenoid is not linear, nor are long solenoids. However, the distribution in a short solenoid is close to linear as compared to long solenoids. I understand your 1/4 wave theory, it isn't new. Our coils are tuned to operate at the full system influence which determines the operating frequency. My only dispute is that the wire length 1/4 wave is not correct in most systems for design purposes due to the various influences on inductance and capacitance. When we build Tesla coils, which is are "target topic" on this list, we must account for as many influences as possible to ensure we build a system which operates to our design. In order for this to occur, the wire length is not the best method because our coils are affected to a degree that the effect becomes a valid consideration (it is no longer a small variant to be ignored).

My first coil was a large 1/4 wave coil. It operated just fine. I took that coil and made it "better" by getting away from 1/4 wave theory. By better, I am considering spark output. The coil was modified from it's original design and the spark lengths with the same power input was a good 40% longer (some of this due to the inductance, some of this due to sparkgap efficiency). We are not making some mysterious Tesla coil for transmitting power. We are consuming power simply to make sparks for the fun of it. For transmitting power or some other novel idea, it is opposite of what you would want.

All systems will have 3/4, 1, 1.5, wave lengths as based from the reference operating frequency. But, they will not operate well at those frequency's as compared to the "natural" system resonant frequency "for the purpose of producing sparks". The very minute the coil is affected by outside influence, the coil is no longer 1/4 wave wire length, and that's just nature taking it's natural course.

Sparks are mostly what this list is about. If a system other than that is to be discussed, then we must certainly differentiate the application. I think possibly this is the defining reason for so much disagreement on these type of topics.

The application defines the discussion parameters.

Thanks for your comments.

Take care,
Bart



Tesla list wrote:

Original poster: Jared E Dwarshuis <jdwarshui@xxxxxxxxx>


Hi Bart:

With standing wave resonance, the change of inductance is a matter of
perspective:
You can change the regions of voltage and current within an inductor.
>From the standpoint of angular frequency, you have changed the
inductance. It is no longer based on the entire length of the
inductor. But from the standpoint of energy you have not changed the
inductance. It will still be the sum of the energy storage from each
region. (like the lumped model)

Inter-turn inductance:

The classic equation for inductance of a solenoid is based on
examining a section from an infinitely long solenoid.  The magnetic
field in a short solenoid is not uniform, hence L is less.

Is we measured L across a few centimeters of wire in an inductor and
then removed the section and measure it again. I would not be
surprised to see a difference in L.  The environments of the electric
and magnetic fields have changed considerably.

Quarter waves:

People build really impressive "quarter wave" coils with enormous top
ends. Large top end capacitances may in fact, maximize displacement
current. These coils are not strictly speaking; wire length resonant,
although they may operate at harmonics of the wire length. I don't
think that multiple wavelength coils can be built using this
approach.

Respectfully: Jared Dwarshuis