TC Primary Capacitors.

["John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

To All -

Back in April Mike H. said he had heard that the TC primary capacitor could
be as large as four times the resonant cap size. I am finally getting around
to commenting on this possibility. This is for a NST 15KV/60ma - 60 Hz -
21000 volts (Vp) - 7.5 watt secs per break output. The efficiency refers to
the amount of energy transferred from the NST output to the primary
capacitor. The equation is

   Watt secs * eff = .5 Cp Vp^2

Listed below are some of the many possibilities.

   Type cap       Cp uf         Eff. %

  Max size         .034         100 %

  Ver 3.1          .020          59 %

  Resonant         .0106         31 %

The max cap size is .034/.0106 = 3.2 times the resonant cap. However, this
cap could not be charged to the peak 21000 volts because the efficiency
would be less than 100% in the real world. What voltage would this cap be
charged to at 59% efficiency?

The Ver 3.1 (JHCTES) cap appears to be a good choice because the efficiency
is reasonable and it is not a "sweet spot" capacitor. Most coilers use caps
about this size for this size NST.

Resonant Cap. It is interesting to note that if the current or wattage did
not change because of the resonant condition this would not be a good
choice. This cap (non resonant) would use only 31% of the possible charging
capacity. This cap does not produce longer sparks because of the size of the
cap but rather because the NST input current is increased. However, it is
not a good choice if you value your NST.

How do YOU determine the size of the primary capacitor for this NST?

John Couture

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