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Re: Arc length equation (fwd)

---------- Forwarded message ----------
Date: Mon, 09 Jul 2007 09:00:43 -0500
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Arc length equation (fwd)


You actually need both for longest sparks. High voltage is necessary to 
create the electrical fields which support initial breakdown and further 
spark growth, while high peak currents are necessary to produce channel 
heating and charge replenishment during spark growth. A low power coil 
with a low capacitance topload will generate high voltages but can only 
source relatively low current. It will produce only numerous thin, 
reedy-looking purple colored streamers. Current is required to form the 
hotter, blue-white leaders that are necessary for longer sparks. Without 
forming hot leaders, the individual small spark channels cool down 
between bangs, and you can not get the bang-to-bang growth necessary to 
form long sparks. Forming and maintaining long, hot leaders simply takes 
power. This is not completely unexpected since the same is true for the 
behavior of AC and DC arcs - leaders and arcs share many characteristics.

John's empirically derived formula encompasses the experimental results 
from a large number of Tesla coils made by him and many others on this 
list. You could actually view it as a form of "empirical optimization", 
since it is based on the results of the best performing coils at various 
power levels spanning watts to huge systems operating at over 100 kVA. 
And, because the equation is based on a parameter that is easily 
measurable (input power), it is actually considerably more useful than 
one based on output voltage or current, neither of which is easily 

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Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Mon, 09 Jul 2007 03:59:03 +0000
> From: Langer Giv'r <transworldsnowboarding19@xxxxxxxxxxx>
> To: mod1@xxxxxxxxxx
> Subject: Re: Arc length equation
> Hi again
> That equation for spark length does show the relation between power output 
> and arc length, but I was looking more for what makes more of a difference 
> in arc length, voltage or current?
> Thanks for the help!
> Daniel.
>> From: List moderator <mod1@xxxxxxxxxx>
>> To: Langer Giv'r <transworldsnowboarding19@xxxxxxxxxxx>
>> Subject: Re: Arc length equation
>> Date: Thu, 5 Jul 2007 22:39:46 -0600 (MDT)
>> Hi Daniel.
>> There was just such an equation posted.  Check out the archives, june
>> 2007, the thread is Jonathon's 6" Coil.
>> Let me know if this doesn't do the trick.
>> Chip
>> On Fri, 6 Jul 2007, Langer Giv'r wrote:
>>> Hey, I am currently in my second year of Engineering at the University 
>> of
>>> Alberta.  I am just wondering if it is possible to derive an equation 
>> for
>>> arc length as a function of voltage and current, given temperature, 
>> density,
>>> dielectric strength, frequency, and any other variables that might come 
>> into
>>> play and make the equation uncontrolled for anything except voltage and
>>> current.  The purpose of this is to create a data set, and plot it onto 
>> a
>>> graph in 3 space to find out what creates the most breakdown, voltage or
>>> current (for a given quantity, as you obviously cannot match current 
>> with
>>> voltage number wise, typically).  Although I might be goin about this 
>> all
>>> wrong and there is a simple answer that I have not yet read.  Oh well, 
>> doing
>>> this is good experience anyways.  I was thinking something along the 
>> lines
>>> of:
>>>     L(E,I) = unknown variables and given quantities.
>>> This multivariable equation will then be partially differentiable 
>> because
>>> there are only two variables as everything else in the equation must be
>>> known.
>>> If the equation is then plotted on a 3D graph with z = L, x = E, y = I, 
>> the
>>> surface graphed should show peaks showing which variable adds to the arc
>>> length the most.
>>> I havent quite thought that far into the fact that voltage and current 
>> are
>>> related (which is probably huge).
>>> Thanks a lot,
>>> Daniel