Re: The Tabletop Tesla Coil Showdown - OFFICIAL RULES and WEBSITE

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

Original poster: "Nicholas Field by way of Terry Fritz <twftesla-at-qwest-dot-net>" <nick.field-at-hvfx.co.uk>

> How long do you think it would take to charge up a cap with a 4/20
> transformer to produce an 18 ft spark? Would you call this continuous
spark
> operation? Don't forget the losses at the very high voltages that are
> unavoidable for producing an 18 ft spark.

Well, Thor processes about 11KW of real power to chuck an 18 foot spark, so
for a 1 second burst we need at least 11kJ stored, using a cockroft walton
multiplier and assuming a charging efficiency of 80% then it would take
about 3 minutes to charge up.  I suspect 'ion cloud' effects mean you would
need more like 5 seconds to reach out to the full 18 feet, but that is
simply a question of bigger cap banks and longer charging times.

> Continuous spark  operation normally implies when using a NST that it
would
> be 100 or 120 sparks per second depending on the input frequency. In other

I deliberately said a 'continuous appearance', ie. a spark that, to the
naked eye, appears continuous.  The frame rate needed in video for a
continuous appearance is 25fps, so I guess that's as good a starting point
as any.

> words a spark for every bang. It is obvious that this hardly ever, if
ever,
> happens as evidenced by the typical eratic spark output. I have never
heard
> of any coiler who was able to match each spark output with a particular
watt
> sec input except for one shot or similar operation. This is a problem with
> Tesla coil operation because spark outputs are not a very reasonable
method
> for rating a TC.

Unreasonable as it may be I think most coilers would agree its the only one
that matters!

> Charging up a cap for a single spark would not qualify for a  continuous
> spark output. The continuous spark output should also have to occur during
> the input time. Before building anything of a questionable nature it would
> be wise to find out from the contest director if it is acceptable for the
> contest. To build something oddball would be risky especially if it
doesn't
> meet the input/output conditions. However, you could still enter the 18
> footer TC for the novelty prize.

I was using that as an example to illustrate the lunacy that could go on if
there were no qualification on duty cycle or pulse rate.  My suggestion was
actually based on the idea of burst mode operation, a large reservoir cap
charged up to a high DC potential and then dumped into the tank circuit
through a charging reactor over the space of maybe 100-200 breaks of the
spark gap.

Safe Coiling,
Nick
_______________
Nick Field, HVFX
www.hvfx.co.uk

> I believe that a controlled (continuous and horizontal) spark from the
> secondary terminal to a ground point does pin down the output enough for a
> contest. It should be noted that the continuous type of spark output is
much
> shorter than the typical random spark using the same input. The bps are
> normally very high with this type of operation. The TC Input could also be
> pinned down by specifying a certain VA amount at 50 or 60 cycles per
second.
>
> For example, I believe that most coilers would agree that a coiler with
only
> a 100 VA input at 50 or 60 Hz (or 4/20 NST) who built any kind of TC and
> obtained a controlled 5 ft spark output for 5 minutes would be the winner.
> This may be impossible but the winner could be the coiler who comes
closest
> to the 5 ft for 5 minutes.
>
> John Couture
>
> -----------------------
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Tuesday, October 08, 2002 11:08 AM
> To: tesla-at-pupman-dot-com
> Subject: Re: The Tabletop Tesla Coil Showdown - OFFICIAL RULES and
> WEBSITE
>
>
> Original poster: "Nicholas Field by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> <nick.field-at-hvfx.co.uk>
>
> Hi both Johns, All,
>
> First off I'm greatly enjoying this thread and if I get a spare moment
might
> put up an entry myself.
>
> The question of duty cycle is a difficult one.  I think perhaps the
> qualifying factor should be that the output spark appear 'continuous' to
the
> eye (probably 15-25pps).  Otherwise the competition could get rather
> meaningless.
>
> I _could_ charge up a big reservoir cap from a multiplier driven by a 4/20
> transformer, then dump all zillion joules into Thor's tank circuit in a
> short burst and claim 18 feet from a 4/20 neon.  However I doubt many
people
> would feel that was in the 'spirit' of the contest!  The reservoir cap
> approach also has the effect of taking a lot of the skill out of the
contest
> and handing the trophy to the guy with the biggest cap bank (eg. Greg
Leyh,
> who has more than his fair share of coiling trophies already!).
>
> For those interested in the ultra low duty cycle end of things I think
Dale
> Hall built a solar powered TC that would charge up over a long period then
> let rip with a few long sparks, I used to have his URL but now it comes up
> dead.
>
> Safe Coiling,
> Nick
> _______________
> Nick Field, HVFX
> www.hvfx.co.uk
>
>
> > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <FutureT-at-aol-dot-com>
> >
> > In a message dated 10/7/02 7:23:58 PM Eastern Daylight Time,
> tesla-at-pupman-dot-com
> > writes:
> >
> >
> > >
> > > John F. -
> > >
> > > Let the contestant use any rep rate he desires. Now that would be a
real
> TC
> > > challenge. Low rep rates would give more spark only up to a certain
> point.
> > > When that point is reached the losses would start to be greater than
the
> > > input and the spark length would remain the same or start to decrease
in
> > > length. This happens often with coilers who add input watts to their
> coil
> > > but beyond a certain point the spark length remains the same length
much
> to
> > > the chagrin of the coiler.
> >
> >
> >
> > John C,
> >
> > A very low rep rate coil simply stores energy for a long period
> > of time and releases it quickly.  Such a set up can give terrific
> > spark lengths for a given input power, but not for a given
> > instantaneous input power of course.  Losses are not much of
> > an issue here.  We're probably talking about different kinds of
> > systems.  In one setup which I called the "DC Disruptive Pulsed
> > Compound Storage Tesla Coil", I was able to get 56" sparks using
> > only 460 watts.  It gave about 4 spark trains per second, and the
> > spark did not appear to be continuous.
> >
> >
> > >
> > > A contest with these rules means that a coiler would have to build
> dozens of
> > > coils of different configurations and inputs to find the optimum Tesla
> coil
> > > that would have the greatest spark length percentage over your
equation.
> My
> > > estimate would be that the winner of this type of contest would have a
> coil
> > > that has less than 1000 watts input. I base this on spark data from
the
> > > List. For example many 1000 watt coils give sparks over 4.5 ft,
> >
> >
> >
> > Many coils that are claimed to be 1000 watt coils, actually draw
> > a lot more than 1000 watts.  Folks use a 1000 watt NST, and
> > therefore call it a 1000 watt coil.  But NST's can draw much more than
> > their rated input powers, esp if powered by a 140 V output variac.
> >
> > but there
> >
> > >
> > > are no coils under 10 KW input giving sparks over 14.2 ft. Larger
coils
> are
> > > even less spark efficient.
> >
> >
> >
> > See my comment above....
> >
> > Note that pole type transformers have an output
> >
> > >
> > > capability of over 10 times their nameplate rating when shorted. This
> means
> > > that the watt input for a certain random spark length would have to be
> an
> > > instantaneous type wattage. This type of metering is never done for
pole
> > > type or similar transformers.
> >
> >
> >
> > The watt input for a pole type TC system tends to remain
> > reasonably steady, although there can be surges especially
> > using async gaps.  It's not customary to try to gauge the exact
> > wattage at the time the spark occurs.  An average input wattage
> > is usually considered to be acceptable.  One can eliminate
> > surging by using a sync gap.  Using a sync gap, the wattage
> > stays steady, from spark to spark.  This would satisfy your
> > desire to equate spark length with input wattage.
> >
> > John F.
> >
> >
> > >
> > > John Couture
> >
> >
> >
> >
>
>
>
>
>