[Prev][Next][Index][Thread]

Re: Spice simulation pictures



Dave Huffman wrote:

If you visit ftp://d0huff.fnal.gov/ftp you should find the JPGs
> along with the spice demo I used. The schematic/spice file is there


Nice simulations!  I was wondering if you have tried to more closely
model the secondary coil, that is to represent the self-capacitance
as distributed along the secondary rather than as lumped at the end.

I've been playing around with PSPICE, and I think that I might have
an explanation for why larger toroids yield better output.  This
effect has been observed empirically by many coilers, including the
folks at the TCBOR, and has confounded me for quite some time, since
if you add capacitance to the output the voltage there must decrease,
if energy is to be conserved.
As it turns out, a Tesla Coil will only act like a resonant xfmr if 
the sec capacitance is concentrated at the top, just like in your 
PSPICE model.  By contrast, if you distribute the capacitance evenly 
over the sec coil then it starts to behave as a tapered transmission 
line, which produces less output.  A tapered xmsn line is not as good 
because it always stores at least part of its energy in the magnetic 
field, and so never at any instant in time is all of its energy 
present solely in the electric field, where it would produce output 
voltage.  So by adding more and more capacitance to the top, the 
currents at all points along the coil are brought into phase, 
yielding the best output voltage.  More C past this point should
start to degrade performance.
How much C is optimum?  Still working on that one, but it's probably
more than an 'proportionally sized' toroid would provide.

-GL