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Re: An Interesting Problem





---------- Forwarded message ----------
Date: Tue, 14 Oct 1997 22:40:35 +0000
From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: An Interesting Problem 

At 10:06 PM 10/13/97 +0000, you wrote:
>
>
>---------- Forwarded message ----------
>Date: Tue, 14 Oct 1997 09:43:45 +1200
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: tesla-at-pupman-dot-com
>Subject: An Interesting Problem
>
>Hello All,
>            I've some up against an interesting conundrum that I 
>expect others have struck at odd times (no, I haven't scoped it).
>I recently fitted more top C to my largest coil, added a turn to the 
>primary and removed about 20% of the primary capacitance to tune it 
>back up. With the radius of curvature at the top it is now having 
>trouble breaking out at the energy level the primary is running at
>(around 2.7J). When it does, it throws a few hot ones, stops dead and 
>either continues to burp in this fashion or needs to be switched off 
>and on again at the wall to get the gap to fire again. The primary 
>voltage is rather low, *but*, it does run reliably and steadily if I 
>add a bump or small point to the terminal in which case it now throws 
>a steady streamer (which waxes and wanes in length as usual).
>    The question: if the gap can clearly fire at this setting, what 
>is stopping it in its tracks when the thing does break out on 
>occasions? Any answers?
>
>Malcolm
>
>------------------------------------------------------

  Malcolm -

  This is an illustration of what I have mentioned in the past about
charging up the capacitance of the toroid. In this case the watt second
input and the source voltage has to be increased to obtain a continuous
spark. The source voltage is the secondary voltage and not easy to determine
during toroid charging operation. What would you estimate the secondary
voltage to be at the primary  2.7 joule operating point? 

         watt seconds = .5 C V^2   

 The rare long spark you are getting is an indication the secondary source
voltage that is charging the toroid is on occasion (after several breaks?)
what is needed for breakout at the toroid. Note that the charging voltage is
a funtion of the watt seconds available. The whole operation of charging the
toroid is complex and one of the reasons that engineering texts state that
the design of Tesla coils is empirical. 
  
  The bump allows the system to operate at a lower source voltage. The
controlled spark measurement can now be used. Note that this measurement
requires a time period of several seconds to be reasonably accurate. In the
CSNotes Tesla found that only about 4 to 10 watt seconds were required per
foot of spark depending on the losses (overall efficiency). 

  It appears you are researching the secrets of those rare long sparks. To
my knowledge none of the present writings on high voltage or Tesla coils has
covered this part of TC operation. The main reason is no one has done the
necessary research to obtain the applicable empirical data. 

 John Couture