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

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

Original poster: "Mccauley, Daniel H by way of Terry Fritz <twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>

>From the referenced web page, comments proceeded by GL>

1.  Must use a Franceformer Model 4020SE 4kV/20mA transformer.  A minimum
of 5 shunts (5 top  / 5 bottom) must be installed and the maximum input
voltage may not exceed 125 VAC (RMS)

GL> 125V?  Looks like I'll have to use a step-up variac so I'm not at a
disadvantage using only 115V ;-)  For the shunts, I think the 5/5 rule is
good as a general guideline, but particularly for folks using a similar but
not identical 4/20 NST, I think the short circuit current needs a specified
maximum value.  For my 4020SE, I use an 8/9 shunt configuration and I'm not
sure I want to use any less for the well-being of my NST.  That results in
a 38mA short circuit current (-at-115VAC).  For a 5/5 configuration, I'm sure
that would result in a significantly higher current, particularly at
125VAC.  If this is a legitimate configuration, the SC current should be
specified as a maximum.  It's an easy measurement to make.  And perhaps
folks with an abnormally high 125V mains should be required to variac-down
to 115 rather than the reverse?  Or would specifying a simple maximum Isc
have the same net effect (not sure)?


DL>>>The 125VAC guideline was introduced to compensate for variations in
home line voltages. Even at my
house, i sometimes read 110-115VAC (particular in summer months) and other
times close to 125VAC.
I think the 125VAC should be a maximum as a lot of people may not have
variacs to control the voltage. 

GL>  I propose these NST requirements, with a consistent after-modification
VA rating:
* Category 1 entries must be a Franceformer Model 4020SE 4kV/20mA
transformer, as above.
* Category 2 entries may be any 4kV NST with short circuit current not
exceeding whatever a 5/5 shunt configuration yields -at- 115VAC.
* Category 3 entries may use any NST whose rated open circuit voltage times
short circuit current does not exceed the above VA rating.  With higher
than 4kV NST, these will enjoy an inherent efficiency advantage over 4kV
users, but it will open the competition up to more people and it will be
instructive to see just how much can be achieved with the same VA.
Observers must simply interpret the results with this in mind.

DL>>>>>This is possible.

2.  Coil must be of a "conventional" type meaning the tank circuit can only
be comprised of the NST, spark gap, capacitor, and primary coil.
Intermediate rectification and voltage multiplier circuits are not
permitted as are the use of additional transformers to step the voltage up.
This includes magnifier type designs.    

GL> It's probably academic since folks are unlikely to bother with a
magnifier configuration on a table-top coil, but I don't see where that
would violate the underlying spirit of the competition - using the same
basic power supply without running it into the danger-zone.  If adding
diodes, 3rd coils, or magic beans between the power supply and top load
improves performance without overstressing anything, then great!  Of
greater concern is governing the gap.  I KNOW that I can get better
performance if I open up my gap.  I would propose setting a .050" maximum
static gap to keep the field safe and level, except that this may hobble
category 3 entries using higher than a 4kV NST.  Maybe just for category 1 &
2?

DM>>>>>>Except how would you regulate rotary gaps??  Also, the voltage
characterics of a gap
are also dependent on the physical characteristics of the gap as well.  A
0.050" wide gap using (2) 3" copper pipes is much different than a 0.050"
point-point gap.



GL> Voltage multipliers and resonant charging schemes don't (I think?)
overstress the underlying NST, so these may be viewed as magic beans.  If
these are used and the modified NST VA rating is not exceeded, it should
fall into category 3.
 
3.  Additional power may be used to provide power for rotary spark gaps,
blower gaps, etc... as long as is does not contribute to the input power to
the primary or secondary.
 
4.  The coil must be able to run for at least five minutes continuously
with no failure prior to making any streamer length measurement.
 
5.  The spark gap may be of any type - static gap, rotary gap, blower gap,
solid state gap, tube gap, etc....
 
GL> A rotary gap with a too-small mains-resonant cap will charge up to much
more than 1.414 * 4kV, and this may be viewed as an unfair efficiency
advantage.  I propose restricting the competition to static gaps in
category 1 & 2.

DM>>>>>>>That sounds good to me.


6.  For the generic category, any 4kV transformer can be used except the
maximum output current must not exceed the measured output current as
measured using the modified Franceformer Model 4020SE above.  Current
output must be measured prior to making any streamer measurements.

GL>  I think verbiage is needed for measuring the output.  Something like:
"Qualifying streamers (apologies to Bert) must connect to a grounded target
at least twice within a chosen 60 second interval.  One-time wonders do not
qualify.  Measurement shall be the straight-line distance from the target
to the nearest point on the top load."  Comments?


Regards, Gary Lau
MA, USA

>Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<dhmccauley-at-spacecatlighting-dot-com>
>
>I finally got around to putting on a page for the Tabletop Tesla Coil
>showdown.
>
>This is the official site where you'll find the rules, results, pictures,
>etc...
>
>Will be updated daily.
>
> http://www.spacecatlighting-dot-com/teslacoil8.htm