Re: 8 kHz Tesla Coil

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 06:27 AM 10/1/2005, Tesla list wrote:
> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
>
> Hi Jim,
>
> I just reread your posting and I'm thinking you are using the skin 
> depth of a flat plane conductor in the equations I quoted.  I think 
> those equations are using a skin depth for a round wire instead of a 
> flat plane in which the equation for skin depth you quoted would not 
> apply.  I dont know if such an equation exist in reality but the 
> site I'm quoting from gives a SD for round conductors that seems to 
> give a little larger value than what Bart's JAVATC program 
> calculates. Several people in this group said that the SD of a round 
> conductor was different than for a flat plane.
>
> Maybe the real question is: if there was a round conductor skin 
> depth equation, would "what I quoted" be true.

Sure.. but there's no simple equation for "skin depth in a round 
conductor".  Whether you start with the flat plane skin depth (which 
is simple) and have some wickedly complex equation to figure out Rac, 
or have a simple equation for Rac, and a wickedly complex skin depth 
equation, it's really immaterial.

The hard part is accounting for the geometry, not the exponential constant.


> If you calculate the resistance of the flat plane conductor that is 
> only one skin depth thick using the flat plane skin depth value, you 
> get the AC resistance.  So, is it possible to do the same with a 
> round conductor using a round conductor skin depth???  Some web 
> sites seems to think so.  See comments below.

Some websites seem to think so, but are perilously light on the 
analytical backup for their assertions.



> > However, those 1-2 mm diameters (approx AWG18 - AWG12) where both 
> > approximations are most inaccurate are also those sizes likely to 
> > be contemplated by high power coil builders who are most concerned 
> > about efficiency.
>
> Not sure what the final answer is other than using the RDRE tables 
> (assuming these are based on measurements and should be considered 
> accurate).  Right now I think the only info provided by any of the 
> TC programs is Rdc.  Maybe an estimate would be better than 
> nothing.  Maybe the RDRE table info could be incorporated into the 
> programs if an equation can not be found.


They aren't based on measurement, but on long tedious analysis and 
calculation, as far as I know.  But, you are right, anything is 
better than nothing.