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Re: An Interesting Problem





---------- Forwarded message ----------
Date: Wed, 15 Oct 1997 13:03:35 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: An Interesting Problem  

Hi John,

> 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.

I'm not sure exactly what you mean here. If you mean that it is 
taking several breaks to charge the terminal up to some humungous 
voltage, I can categorically say that is not happening. Never has on 
any of my systems.

 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? 

Around 300 - 350kV based on an estimated transfer efficiency of 70 - 
80%. It won't be far off and I now have a means of measuring this 
efficiency pretty accurately.

>          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. 

I really must reiterate that that scenario just isn't happening. I 
can buy that some succesive breaks are building an ion cloud in the 
vicinity of the terminal but that is the extent of it. There is no 
way oscillations are summing themselves with successive breaks and 
there is no way the terminal can charge up to some DC value.  
    I saw a very similar thing happening with those single shot 
experiments in the weekend. Give it one alone at a slightly reduced 
energy and no pop from the top. Give it several per second and 
streamers start appearing but there is no way I have ever or ever 
will build a system capable of ringing for a millisecond or more. In 
the case of the coil in question, it would throw hot fat ones for 
maybe half a second (50 breaks or so) and then stop dead. I do have a 
possible reason for its behaviour but I am listening to others first.

>   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). 

I am doing far better than that. I note that in many writings Tesla 
was somewhat loose in his terminology. Richard Hull can correct me if 
I'm wrong but Tesla often used Watts when he was really talking 
Joules. The system in question has thrown sparks around 5 feet with a 
primary energy of no more than 3J pumped 100BPS. Well worth noting 
that I have yet to obtain that efficiency in smaller coils but all 
that leads me to strongly suspect that the impact of low frequency 
operation on streamer formation speed has more to do with it than 
coil size as such. I have obtained sparks around 2 feet long on one 
system on a single shot basis with 10J. But I think this is all 
getting off the track anyway.

>   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 

Hmmmm...   Well, I don't really think that has a bearing on this 
particular problem but thanks for airing your thoughts anyhow.

Cheers,
Malcolm