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Re: SG - The anatomy of the spark?

In a message dated 4/28/00 4:12:06 AM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original Poster: "Bob Berg" <berg_bob-at-hotmail-dot-com> 
>  
>  It seems to me that some of the easiest ways to improve coil output 
>  performace can come from changes in the spark gap.  I'm no expert and 
would 
>  like to know more about what happens in a spark gap.

Bob,

Many small coils that are built by beginners, use a poor quality gap
which overheats and fires at a too-low voltage, or power-arcs.  Under
these conditions, any gap improvement will make a big difference.
Once you have a good quality gap, it's much harder to get an
improvement by improving it more.  Of course in an NST system, one
can often get a big improvement by using a sync rotary gap.

>  
>  In a perfect world how would we want the spark gap to act?
>  What is the resistance of a spark gap when it conducts? Can this 
resistance 
>  be reduced?

We want to arc to act as a lossless switch, which fires at a certain
voltage, or at a certain time.  Ideally it should be able to quench at a
time when all the energy in the primary has transfered to the secondary
(first notch quenching).  If it doesn't quench at this time, some energy
may transfer back to the primary, and make another round trip and
thereby increase the losses.

>  What is the diameter of the arc in a spark gap, is it bigger with more 
>  current?

I seem to remember that the arc diameter does increase with more 
current.

>  Quenching, From my understanding, quenching is act of "Blowing out a the 
>  spark in a spark gap.  But I don't understand why is so important.  If I 
>  "Blow Out" the spark  won't I prevent the capacitor from dumping ALL of 
its 
>  energy into the primary?  Or is it the act of quicky turning off the 
current 

First of all, you'll never be able to quench the arc too soon, so that is
not an issue.  Also, the arc will quench on its own without any special
efforts once the energy has gone into the sparks or is otherwise 
dissipated.  Quenching is important, but interestingly, good quenching
is often dependent on other factors than the gap itself.  If the coil is
producing a good head of sparks from the toroid, this will drain the
energy out of the system quickly and cause the gap to quench faster.
> 
>  in the primary for a sharp collapse in the feild in the primary that is so 
>  important?

A sharp collapse is not an issue.  

>  Is it possible to over quench?

For all practical purposes, no.

>  Also, can some one give me a simple understanding of "Ringing" in the 
>  primary.  I get the feeling that Ringing is the oscillations that occur in 
>  the primary tank circuit when the Capacitor is discharging through the 
gap.  

You are correct.


The primary is supposed to ring like a bell when the gap fires.  As the
primary energy rings down, the energy transfers to the secondary which
then rings up.  When all the energy has transfered from primary to
secondary, then the gap should ideally quench.  The transfer process
takes about 8 RF cycles for a typical coil.  Tighter coupling will cause
faster energy tranfer, but make the quenching more difficult, thus the
coupling adjustment is a compromise.
> 
>  If I'm correct no explination is needed.  However, what I confused about 
is 
>  when the capacitor is discharging into the primary what is happening to 
>  power of my NST going into the cap?.

The NST is basically shorted out when the gap is firing.

Cheers,
John Freau

>  
>  Thanks
>  Bob
>