Re: Spark length equation and pri. program

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 6/27/01 1:26:58 PM Central Daylight Time, tesla-at-pupman-dot-com 
writes: 



>
> I have been thinking lately about the relationship between spark length and 
> voltage. current isn't a factor is it? for example, 12kV can jump about 
> half and inch, and 1MV can jump, (guessing here) two yards? I was trying to 
> figure out an equation to find max. spark distance by voltage, but haven't 
> been able to do so. Someone had to already find it, and I'm probably just 
> re-inventing something, but hey, its worth a shot... 


Jonathon, 

I'm certainly no expert on this, but it is my understanding that there 
are a number of variables that affect spark length besides voltage. 
Factors such as frequency, electrode surface(s), atmosphreic con- 
ditions, ect. also play an important role in spark length. So, that 
makes it next to impossible to make a truely accurate linear spark 
length vs voltage chart that would apply in all circumsances :-( 
One of the best logarithmic graphs showing the relationship of 
spark length vs voltage is the graphs in John Couture's Tesla Coil 
Construction Guide, page 14-9, and Tesla Coil Design Manual, page 
12-2. However, you must remember that these are graphs of 
voltages from Van de Graf type DC power supplies from large dia- 
meter spherical electrodes. The higher frequency AC from a Tesla 
Coil would jump further at a given voltage than these graphs would 
show. The question is, 'how much further?'   

Also, Tesla coils are able to take advantage of spark propagation 
at higher break rate rotary spark gaps. This allows for even longer 
spark formation at a given voltage, assuming that the Tesla primary 
circuit is capable of supplying sufficient power to continue feeding 
the spark. I don't fully understand all of this myself, but this is pret- 
ty much the jist of it in a nutshell. Other more knowledgeable list 
members could probably explain all of this better and I'll leave fur- 
ther explaination to them :-) but the bottom line is that spark length 
is not a very accurate and reliable way to determine voltage in Tesla 
coils. Formulae like (SQRT {2eJ/Ctotal}) are sometimes used to give 
an approximation of the peak output voltage. Hope this helps some. 

Sparkin' in Memphis, 
David Rieben