# Re: [TCML] confused

```Hi Gary,

```
Javatc has 3 spark length values. The first is the JF equation with some DC Cox efficiencies incorporated based on secondary diameter. The other 2 spark length equations are of my own doing. They are a little more involved and reside in the rotary and static gap sections. For example, the rotary equation is:
```-----------------------------------------------------------
These are for average random free-air spark length.
```
The equation is derived from John Freau's spark length equation (1.7 x sqrt(input watts)).
```
Spark Length (inches) = sqrt(VA) + (sqrt(eJ x BPS x 1.263) x .75)
Where:
VA = input volt amps = transformer effective input power.
eJ = effective cap energy in joules  = 0.5 x C(tank) x eVp^2 = see below.
BPS = break per second.
eVp = effective cap voltage  = x_vp*(1-pow(2.7182818,(-rsg_fr/rsg_t1))).
x_vp = transformer peak output voltage.
rsg_fr = rotary gap firing rate (1/bps).
rsg_t1 = time for cap to charge to one time constant based on cap size and transformer current.
The .75 at the end of the equation is an efficiency factor.
-----------------------------------------------------------

Although I'm looking basically at the energy across the gap (from a numbers standpoint),
gap efficiency is dictated by the tank circuit and the unknown gap itself. It paces well with John's equation,
but it is most helpful when the rotary or static gap is poorly designed. It then shows a big difference and
causes one to look a little closer. That is the basic "reason" for the equation. Gap efficiency is obvious to
most of us, but often, simple parameters or geometry can affect the gap as well and that's really what this
equation is attempting to help with.

So yes, only something to strive for and does not necessarily indicate
that a coil will achieve the spark length predicted. In some cases, coilers do better, but in most cases, the don't.

Take care,
Bart

Lau, Gary wrote:
```
```I think that JavaTC estimates the spark length of a coil only by the power consumed by the transformer, so it would give the same answer for both a 15/30 and 7.5/60 NST.  It is believed that higher voltages may actually result in greater theoretical efficiency for the same power level, due to lower losses in the spark gap, but I don't know that this has ever been experimentally confirmed, as it's impossible to make two coils where the only difference is the NST.  Too many other necessary differences would make it difficult to reach a conclusion.

Regards, Gary Lau
MA, USA

```
```-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of douglas smith
Sent: Wednesday, June 18, 2008 12:54 PM
To: tesla@xxxxxxxxxx
Subject: [TCML] confused

all this talk about hooking  ac transformers in series has got me really confused.
i always thought  that you could connect DC output transformers in series
but not AC.
i know that there is some kind of circuit that allows you to do so but just
putting two nst's in series sounds like trouble to me.
why would you want to anyway?
in designing some 15 different possible coils with javatc it seems to me that
a higher voltage is not always that necessary.
example: i would get the same spark length and power factor with using a
15000 v @ 30 ma as i would with a 7500 v @ 60 ma
of course I'm no expert the math just seems the same (P=I x E) and also with javatc
I'm sure that there is a limit on how low you can go with the voltage vs. current
but it does seem to me that the major rule of thumb is the power factor.

```
```
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