Re: dual MOT Tesla coil design is complete (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi Gerry,

Yes, I agree with you here. Since your coil yields
a 7 ft. arc from 2 kW of input power, which is
quite impressive performance, I might add, that
means that it would require 8 kW of input power
for it throw 14 foot arcs, assuming that your coil's
physical parameters would permit this kind of pow-
er processing without "meltdown" ;^) And that would
still be very impressive performance at that power
level. I suppose if you followed this same progession
upward, your power level would "cross" you feet of
spark length around 23 kW so at this particular point,
a coil would yield "1 ft. per kW". My Green Monster
coil: http://www.teslauniverse.com/members/drieben/
draws around 80 to 100 amps at 240 volts input to yield
12 to 14 foot sparks (w/variac @ ~85%), so it's not quite
so efficient. However, I do now have a forced-air cooled
1.25 Ohm power resistor that I can add in combination with
the inductive ballast to further ballast the input to the pole pig
transformer and I've noticed that the additional 1.25 Ohm
resistance really cuts back the current draw to around 55 to
60 amps with the variac turned up all the way to 100% (280 V)
The resistance was added more for the x-ray transformer
that drives my large Jacob's ladder than for the coil, though,
since I designed my control panel to drive seperate compo-
nents from the main Tesla coil circuit. However,
the output sparks tend to be slightly shorter with the
resistance than without, but the dramatic difference is
in the BRIGHTNESS of the output sparks! The sparks
are probably 3x brighter without the resistive ballast than
with it! Also, spark breakout occurs at a lower variac
setting w/out the resistance than with it and this would be
expected. I can hardly turn the variac all the way up to 100%
w/out the resistance ballast because the RSG quenching action
starts failing (choppiness) and the current draw reaches the
110 to 120 amp range!

Anyone else have data from using resistance in combo with
inductance for ballasting their large coils? In my experience,
the resistance does tend to smooth out the choppiness of an
overpowered/poorly quenching RSG (good), but it also
really waste power in the form of heat (bad).

David Rieben


----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, November 01, 2006 11:07 PM
Subject: Re: dual MOT Tesla coil design is complete (fwd)


> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi DC,
>
> What is this 1kw per foot of spark for classical coils???  It has
> always been a sqrt(power) and not a linear relationship, has it not?
>
> BTW, my 2KW (real wall power) classical coil generates over 7 foot
> arcs. So this would make it 285 watts per foot by this reasoning, yes???
>
> Gerry R.
>
>
> >Original poster: "resonance" <resonance@xxxxxxxxxxxx>
> >
> >
> >with IGBTs the rules are changing.  Their much higher switching
> >efficiency and lower losses of heat and light lead to 450 Watts / ft
> >of spark performance as opposed to 1 kW / ft required in classic coils.
> >
> >
> >Dr. Resonance
> >----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
> >To: <tesla@xxxxxxxxxx>
> >Sent: Wednesday, November 01, 2006 5:59 PM
> >Subject: Re: dual MOT Tesla coil design is complete (fwd)
> >
> >
> >>Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> >>
> >>Hi Terry,
> >>
> >>This would be great, but what ever happened to the sqrt(power)
> >>relationship???
> >>
> >>Gerry R
> >>
> >>>Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
> >>>
> >>>At 10:48 PM 10/30/2006, you wrote:
> >>>>Hi DC,
> >>>>
> >>>> From what you say below, it sounds like you have the design but
> >>>> have not built it yet??  If this is true, where did the 7.5 foot
> >>>> arcs come from??
> >>>>
> >>>>Gerry R.
> >>>
> >>>My SISG does about 28 inch arcs at 4800 SISG firing volts with a
> >>>165nF primary cap.  It would do about 42 inches if I let it loose
> >>>with one MOT...  If DC can get 4800 Watts out of two MOTs, then
> >>>the spark length directly doubles to 84 inches or 7 feet.  But he
> >>>is using a bit larger primary cap too...  So 7.54 feet is about
> >>>right.  I am a little concerned about getting 4800 Watts out of
> >>>just two MOTs.  But DC might know tricks I have never dreamed of ;-))
> >>>
> >>>I have not thought much about the dual MOT SISG system...  But
> >>>others are now thinking far faster than me on SISG things ;-)))))
> >>>
> >>>Cheers,
> >>>
> >>>         Terry
> >>
> >>
> >>
> >
> >
> >
>
>
>
>