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TC Secondary Terminal Design


  All -

  Finding the proper size secondary terminal has now become easier when
using a new(?) equation that I have derived from several theoretical
equations. This is not a precise solution but does get you a ballpark figure.

 The sizing of the secondary terminal capacitance is part of the tuning
process and must satisfy the  Lp Cp = Ls Cs  equation. However, the size is
also determined by the input voltage and wattage. When the input voltage or
wattage is increased the secondary terminal capacitance should be increased.

  The equation I derived to do this is as follows:

      Cs = 12.34 * cuberoot(KVp^2 * Cp)

     Cs in pf      Cp in uf

  Note that Cs in this equation is based on input voltage and  also on the
input wattage when  
  Cp = J/Vp^2  and  J = Input watts/ Breaks per second

  The equation is derived assuming the following:

  The secondary terminal is a sphere and

  Cs (pf) = sphere dia * 1.41    

  Secondary kilovolts = sphere dia * 32.5   

  Sphere breakout is 65 KV per inch radius 

  KVs = KVp * sqrt(Cp/Cs)

  When the secondary capacitance is found the approx. sphere dia can be
found by subtracting the sec coil self cap from the secondary capacitance.

-------------------------------------

  EXAMPLE -

  Given Primary volts 15 KV rms * 1.4 = 21 KV peak
        Primary wattage 1000
        Breaks per second 120

  Find  Primary capacitance Cp
        Secondary capacitance Cs

  Watts per break = 1000/120 = 8.33
  Cp = 8.33/21^2 = .019 uf
  Cs = 12.34 * cuberoot(21^2 * .019) = 25 pf

  Sec volts = KVs = 21 * sqrt(.019/25*10^-6) = 579 KV
  Sphere dia = 579/32.5 = 17.8 inches

  For a check use  Cs = sphere dia * 1.41 
                      = 17.8 * 1.41 = 25 pf as above.

-------------------------------------

  This gives the approx. secondary terminal size when it is a sphere. The
equations would have to be modified for a toroid. Does anyone want to give
this a try?

  Note that the Cp/Cs ratio is important because it fixes the Ls/Lp
inductance ratio. You only have to decide on the secondary inductance or
the primary inductance. The operating frequency can be found by 
    F = 1/(6.283 * sqrt(L * C))

  Note also that this explains the apparent dilemma in the equation
  KVs = KVp * sqrt(Cp/Cs)  that indicates the secondary capacitance (Cs)
should be made very small to obtain a large secondary voltage.
 
  I would be interested in comments from coilers on this somewhat novel way
to find the secondary terminal size.

  I am obliged to make the following comment - the above can be more easily
implemented using the JHCTES computer program. Please forgive.

  John Couture

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