Re: Theory - primary cap duty -transformer output current

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi,

At 02:32 AM 7/3/2001 -0600, you wrote: 
>
> My inquiry focuses on transformer current and the primary cap.
> My understanding is that once the primary cap is charged and the firing spark
> occurs that the transformer's current during the HV pulse and "ringing" are
> no longer a factor, that the energy stored in the primary cap becomes the
> sole provider of current in the tank circuit. 


Yes.

>
> Once that arc is quenched then the primary cap is again charged. So how does
> transformer current fit into the scheme of things? If that cap is allowed to
> charge within 90% of the voltage available before discharge then where does
> transformer current fit in? Does higher current allow quicker charge time?


The transformer's current rating determines how fast and what size of capacitor
can be charged.  Assuming you only have 1/120th of a second to charge the cap
to say 20kV, a smaller current transformers will only be able to charge small
caps while large currents can charge proportionally larger caps.  Since the
energy stored in the primary cap is proportional to the size of the capacitor,
you need higher and higher current transformers to charge larger and larger
caps.  Even though a pole pig (10kVA) and a 30 mA neon sign transformer have
the same voltage rating, the pole pig can deliver say 500mA or well over ten
times the energy of the smaller transformer.  The small transformer may only
charge a 15nF cap while the pig will charge a 400nF cap to the same voltage
given the same time.  The following link shows charts of various transformers
and the capacitances they can charge at a given a BPS rates.

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm

The paper below may also be of interest:

http://hot-streamer-dot-com/TeslaCoils/MyPapers/modact/modact.html

>
>  
> I can see where firing at zero-crossing is also advantageous, allowing the
> cap to "see" the full transformer output voltage and eliminates shorting the
> transformer secondary during discharge.
>  
> Somewhere I think I have something missing or thinking wrongly.


Your pretty close :-)

There are also LTR or resonant charging effects that use the energy stored in
the NST's inductance (as current) to help charge the cap faster with inductive
kick effects.  LTR coils can charge significantly higher value capacitors (x2)
given the same NST by using careful gap timing.

Cheers,

        Terry