[TCML] MAX SPARK FOR FIXED VOLTAGE

[bartb]

Hi Dex,

Your question is good, but it is based on the assumption that potential 
voltage equals a given spark length. This isn't the case in a Tesla coil 
output spark like it is in the potential required for 2 bodies of some 
size and geometry to arc to one-another. Over and over again it's been 
shown that spark "lengths" in TC service follow a power curve. It 
depends on the power delivered to the streamers and time. The actual 
voltage at the top load cannot be directly linked to spark length 
without the inclusion of the change in current over time. The main 
parameters that supply this are the inductances, capacitances, power 
supply, and top load limit on voltage.

A better question and answerable question is what is the approximate max 
spark length possible for a given power. Then we can easily quote John 
Freau's 1.7 x sqrt(input watts) spark length equation which has held 
well for more than a decade. There are certainly situations which affect 
even this spark length, but it is the most accurate equation for spark 
lengths over the spectrum of variations with systems.

I can accurately say that if you used 100kV, 200kV, 300kV and kept power 
unchanged, then for a 1000W coil, expect the following ideally.
1) 100kV = 53.7"
2) 200kV = 53.7"
3) 300kV = 53.7"

This is not a trick. It states that the terminal voltage is not 
affecting the spark length directly. Maintaining power delivered to the 
spark at 1000W, the current is adjusting (10mA, 5mA, 3.3mA). However, if 
you were to double the power to 2000W, then (ideally):
1) 100kV = 76"
2) 200kV = 76"
3) 300kV = 76"

Note the spark length increased only by a ratio of 76/53.7 for twice the 
power. This is the reality of Tesla Coils. BTW, by "ideally" I'm 
referring to the fact that not all coils will achieve the spark lengths 
for the power given. Most will be below this length, some at this 
length, and a select few a little better (John's system during these 
tests were quite efficient).

Another reality not thought about is that you will be hard-pressed to 
keep the top terminal below 100kV and above 400kV. The top terminal 
limits voltage but can also break out at peak voltages which are far 
from average voltages. From a completely academic standpoint, it's fine 
to contemplate the top terminal voltage, but for breakout, consider the 
peak voltage the top terminal will see (punching out). However, after 
the initial breakout, the current delivered to the streamer is what will 
dictate to some degree the spark lengths achievable. The power is what 
pumps the current into the spark channel (and the more power, the longer 
and higher the current is available).

I can probably speak for a lot of coilers when I say that reducing gap 
losses (more power delivered in the emf at the primary and thus the 
secondary) and more power in the supply itself is what has increased 
spark lengths on any given coil. There is of course secondary 
inductances better equipped than others at delivering the power to the 
top terminal and the terminal C itself determining when breakdown 
occurs, but it is "power" that ultimately delivers short or long sparks 
(power is the predominant player with spark lengths).

Take care,
Bart



Dex Dexter wrote:
> I have a good question I don't know answer to.
> QUESTION:
> What is aproximately maximum spark lenght possible for a given output voltage Tesla system generates?
>  
> Regardless of the efficiency,how long spark can be produced by a Tesla-type impulsive devices with voltage levels:
> 1) 100 kV
> 2) 200 kV
> 3) 300 kV
>  
> Can a high power impulse source,like a Tesla transformer,put out a 10 feet long spark with 'only' 100 kV voltage peaks?
> To accomplish that it is free to use any power input level,any size and shape of  a terminal capacity,any firing rate wanted,andthe best high frequency excitation waves mix.DRSSTC,VTTC,etc.
> The only limiting thing is not to exceed 100 000 V terminal potential.
> Supposing a normal atmosphere enviroment is that possible?
> I know that in no circumstance 50 kV can close 5' wide gap unless directly conducting path is formed somehow,or a
> strong external ionization occurs ,like exposure to a flame,extremely powerful lasers,but Tesla transformers are the 
> champs of 'spark pumping' and I was wondering what could be done with 100 kV.
> Thanks for  your answers and explanations.
>  
> Dex  
>
>
>
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