Re: Modeling Secondary Inductance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Rscopper-at-aol-dot-com>

You have some good questions.  I haven't read Brent's book, but I'll tell you
about WinTesla formulas. 

The formulas in WinTesla are a collection from 4+ years of Tesla list
conversations, I tried not to discount anyone's ideas and include all the
models.  I did this because there isn't one "grand unified theory" on Tesla
coil modeling.  Some items that make sense for a small coil seem to go south
with a large coil.  Many items are hard (or impossible) to measure and prove,
so emperical data is all we have to work with. 

For example, it seems that everyone's primary transformer is different, so a
model for a distribution transformer doesn't fit for a neon sign transformer. 
If one person uses speaker "Monster Cable" to make a secondary, and one uses
silver plated wire wrap wire, and another uses double formvar Essex magnet
wire, the model is different.  The formulas don't have models for various
secondary forms - damp cardboard tube will have different properties than SCH
80 PVC pipe.  The models don't correct for temperature and humidity either. 
They are only a starting point to help "tune" the coil.  My measurements have
NEVER exactly matched any formulas to date. 

Feel free to come up with your own theories and post them for the rest of us. 
High voltage and plasma arc science isn't very black and white.  If it was,
we'd all be riding levitating scooters running on fusion reactors (and I WANT
one of those!). 

You'll probably get a bunch of comments on this topic. 

R. Scott Coppersmith 



In a message dated 9/9/01 9:21:27 PM US Eastern Standard Time, tesla-at-pupman-dot-com
writes: 



>
> Original poster: "Janet Johnson by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jpjmassage-at-earthlink-dot-net> 
>
> Hi everyone, 
> I was using WinTesla to design my coil and started playing with the Spice
> model 
> provided.  A book I have (The Tesla Coil Book by Brent Turner) describes the 
> secondary as a series resonant ckt but the Spice model from WinTesla shows
> the 
> self capacitance plus the toroid cap in parallel.  This makes sense to me
> since 
> self-capacitance comes from inter-winding and planar, both of which are in 
> parallel with the coil inductance.  Is the book wrong or am I missing 
> something?  Another point of confusion for me is how the secondary is treated
>
> both as a quarter-wave resonator and an LC resonator.  The first is a 
> transmission line concept (i.e. distributed inductance and capacitance) while
>
> the second is a lumped element concept.  Is this like wave/particle duality
> of 
> light or something?   
> Something else I noticed about the model was that when the spark gap switch 
> closed, the coil output spiked up and rang down.  I thought the secondary 
> oscillations built over successive firings until the voltage reached a 
> threshold and blasted out sparks.  I read an analogy with lasers somewhere...
>
> Anyway, if some of you theoriticians out there wouldn't mind setting me 
> straight on the concepts, I would be most grateful.  I am an engineer so I 
> can't help having to know exactly how these things work! 
> Thanks in advance 
>
> Jeff Johnson 
> Salt Lake City 
>
>