Re: Tesla Coil Formula

["Tesla list" <tesla@xxxxxxxxxx>]

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