Re: Capacitor in series with transformer or S.G ? What is right?

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Original poster: "Luc by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ludev-at-videotron.ca>


Hi Harvey

May be I could help you with this one; after firing, the cap is
discharge and a discharge cap could be considered like a short,
the supply current have a less resistive path in the cap then in
the gap this is why the gap go off after bang. It's important to
use a balance cap for the supply because if you have to much
power the cap will charge to fast and the gap don't have time to
get the ion out and could ignite at lower voltage and go in power
arc mode.


> The thing that I always had problem fathoming, is that
> when the arc gap fires, it then appears as a short to
> the power supply, yet at the same time this does not
> cause a great jump in (transformer primary)amperage
> input. The explanation given for the use of the rotary
> arc gap seems to make this comprehensible, because
> then the electrodes only come together for arcing when
> the source AC cycle goes to its zero point in the
> cycle, because the rotation of the arc gap electrodes
> is timed to the source frequency. If the gap fires at
> its AC zero crossing point, then a short at zero
> amperage input is of no consequence.
> 
The main reason we use a rotary is for retarding the firing a
little permitting to charge a bigger cap but you fire near the
max voltage of the cycle  ( Just a little bit after ) 


> Thus the gap operated in static case must be modeling
> the same behavior? In one half cycle of source
> frequency, the cap must be fully charged,(if the
> supply can meet the demand of current made by the
> capacitive reactance being used) The resistance of the
> arc gap is such then that when the cap is fully
> charged at the source frequency, it then discharges
> across that gap to produce the hf oscillation on the
> tank itself. But since the time for cap charging must
> occur during the half cycle of the input, by the time
> the discharge at gap occurs the source frequency must
> be coming close to its zero crossing point.

No cap discharge is really fast ex: you have a primary tuned at
150 Khz with a typical coupling the cap take 10 cycle to
discharge, often the coil will not break at first notch assume
that it break at the third notch that is 10 cycles multiply by 3
= 30, 30 cycle at 150 KHz is .0002 second, half of half a cycle
in 60 cycle is .004 second then the discharge is 20 time faster
than the time the supply take to pass from V max to 0V.

 Thus the
> arc gap already models what the rotary scheme
> manipulates,No?
> 
> Here is where another question comes up. Suppose we
> have a TC driven from a NST 15,000 volt 30 ma supply.
> By calculating the reactance of around 50 nf, we also
> find that is the ~value of capacity that would would
> allow that 30 ma conduction to occur. Doesnt this
> imply then that if we drive a TC with cap values above
> that 50  nf in its tank circuit,from this transformer
> NST , the source would not be meeting the demand? 
Yes

> HDN
> 
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Cheers,

Luc Benard