# Re: Tesla Coil toroid Size

```John, c'mon:

> Original Poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
>
>
>   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

Above you correctly equate energy with W-s

>   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

And here you are equating power with W-s. They can't both be right.
The reason for the error in this bit is that you have omitted the
"/s" from the "Break" part.

e.g. 80 Breaks/s * 76 W-s = 6080 W

>   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

That is a complete guess at best. In fact I have measured a transfer
efficiency approaching 90% on a small coil. I see no reason why it
should drop so drastically on a large one.

>   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.

It doesn't, period. If anything, Ep would be lower as breaks
increased because of easier gap firing due to heating. I will be the
first to put my hand up and say that Greg's data confirms what I have
found experimentally.

Malcolm

>
>   John Couture
>
> -----------------------------
>
> 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
>
>
>
>

```