Spark Gaps

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Saturday, April 11, 1998 11:19 PM
To:  Tesla List
Subject:  Re: Spark Gaps

John, antonio, and all,

Both gap closing AND opening functions are important for Tesla Coils. 

Closing should consistently occur at a voltage which does not overstress
the supply trasnformer or the tank cap, but at a sufficient voltage
which results in the desired per-bang energy. From this perspective a
multiple-gap static/vacuum gap or synchronous rotary gap are ideal.
Improper closings ("misses") are particularly damaging when an
asynchronous gap is tied to a system which resonates the tank cap and
power source leakage/ballast inductance at 50 or 60 Hz. - a sure NST or
tank cap killer.

Proper gap opening serves two functions. The more commonly accepted
function to "strand" energy in the secondary once all primary energy has
been transfered (ideal "quenching"). Ideally, this will occur upon
completion of the FIRST primary-secondary energy transfer (sometimes
called the first primary current notch). The second and equally
important function is to prevent power arcing of the HV supply. This
becomes particularly critical when the HV supply can provide enough
cap-recharging current such that the gap reignites before recovering its
full breakdown voltage. The resulting power arc effectively shorts out
the HV power source.

Under heavy secondary streamer loading, nature tends to take care of
quenching at the first or second notch AS LONG AS YOU PREVENT POWER
ARCING. Under these conditions, you will get similar performance from
static/vacuum, air blast, or rotary gaps. With neons, power arcing is
less of a problem - hence the excellent performance seen with
static/vacuum gaps. Pole pigs, particularly when operated at higher
power levels, often demand the forceful arc-breaking that comes from a
rotary gap.

BTW, as far as I know, there's NO experimental evidence that the spark
gap in a disruptive Tesla coil EVER opens at other than ZERO primary
current... and at or near zero primary energy. Thus, there's
correspondingly no evidence that a true disruptive Tesla coil (excluding
a kicker coil...) ever operates in the rapid -di/dt realm of an
induction coil. 

Safe coilin' to you!

-- Bert --

Tesla List wrote:
> ----------
> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:  Saturday, April 11, 1998 2:28 PM
> To:  Tesla List
> Subject:  Re: Spark Gaps
>   All-
>   I agree with Antonio. Why is the Tesla coil called an air core transformer
> if it operates as an induction coil?
>   It is my understanding that the Tesla coil utilizes dampened waves and
> resonance. The spark gap characteristics should optimize this type of
> operation. The spark gap CLOSING is important for Tesla coils (Peak of the
> voltage wave). The spark gap OPENING is important for induction coils (di/dt).
>   But why is quenching important for Tesla coils? The times that quenching
> occurs are certainly different with fixed gaps compared to rotary gaps. One
> should be better than the other.
>   John Couture
> ------------------------------------------------
> At 11:56 PM 4/9/98 -0500, you wrote:
> >
> >----------
> >From:  Antonio C. M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> >Sent:  Thursday, April 09, 1998 1:11 PM
> >To:  Tesla List
> >Subject:  Re: Spark Gaps
> >
> >Jim Lux wrote:
> >
> >> 3) Faster interruption of the spark. As opposed to just waiting for the
> >> current to go through a zero, the gap is physically separated. The sudden
> >> circuit opening causes the voltage across the primary inductor to rise,
> >> inducing a similar rise in the secondary. The faster the interruption
> >> (di/dt) the more the rise.
> >
> >Do this really work? This would be like operating a Tesla coil as an
> >induction coil. The theory saying that there is a great increase in the
> >secondary voltage or a two-coil system after the opening of the spark
> >gap (Corums) may be due to this effect (otherwise I don't see how).
> >
> >Antonio Carlos M. de Queiroz
> >http://www.coe.ufrj.br/~acmq
> >
> >
> >
> >