# Re: Tesla Coil toroid Size

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Greg -

I think you are taking too much for granted by assuming the TC primary
cap energy is not changing when the breaks are changed. This parameter
should actually be measured. However, I agree that the spark length depends
on the number of breaks.

In my TC Construction Guide I show the following equation (modified) -
watts seconds = .5 x Cp x Vp^2 x BKS/EFF
It is obvious from this equation that the total watt seconds will
increase as the breaks increase and the sparks increase.

The calculations to obtain the watts per foot of spark using your data
are as follows -

Your estimated 76 watt seconds is from -
joules = .5 x .225 x 10^-6 x 26000^2 = 76 watt seconds

This gives total watt seconds -
1 Break = 76 x 1 = 76 watt seconds
80 Breaks = 76 x 80 = 6080 watt seconds
350 Breaks = 76 x 350 = 26200 watt seconds

The above does not take losses into account. The losses would approx
double the above -
1 Break = 76 x 2 = 152 watts/2.5 = 60.8 watts per foot of spark
80 Breaks = 6080 x 2 = 12160 watts/4 = 3040 watts per foot of spark
350 Breaks = 26200 x 2 = 53200 watts/25 = 2128 watts per foot of spark

It is my understanding that these were not controlled sparks so they
cannot be compared with that type of spark. However, your data does not
appear to agree with what other coilers have found with their coils using
the data I have collected. I believe this is because you assumed the TC
primary cap energy did not change when the Breaks were changed.

John Couture

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At 02:28 AM 9/16/98 -0600, you wrote:
>Original Poster: Greg Leyh <lod-at-pacbell-dot-net>
>
>John H. Couture wrote:
>
>>   I was hoping that it would be possible to get some idea of the input
>> energy in a certain spark length by this test. For example if the spark
>> increased one foot and it was found that the input energy increased 2 watt
>> seconds we could say the energy in the spark is apparently 2 watt seconds
>> per foot of spark.
>>   This could help verify some of the other methods we are using to find the
>> watt seconds per foot of spark.  -JHC
>
>
>The notion of 'watt seconds per foot of spark' is incomplete at best,
>since the arc length is completely dependent upon the break rate, or
>BPS.
>
>Here's an example:  My primary capacitor is 0.225uF, and operates at
>26kV.
>The Vpri is *not* adjustable in this design, which means that the Ep is
>independent of the break rate, and therefore is always 76 watt-seconds.
>
>At a BPS of   1, the sparks at the toroid are about 2.5 ft long.
>At a BPS of  80, the sparks at the toroid are about 4.0 ft long.
>At a BPS of 350, the sparks at the toroid are about 25. ft long.
>
>The coil gains a factor of 10 in spark length while the energy
>per pulse in the primary remains constant, at 76 Joules!
>The dramatic increase in spark length is due solely to the coil
>exploiting the ion lifetimes at the higher break rates.  The
>coil *DOES NOT* generate higher voltages at higher BPS values.
>--
>
>
>-GL
>www.lod-dot-org

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