Re: Coil Efficiency (quenching)

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Tuesday, July 29, 1997 3:11 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Coil Efficiency (quenching)

Hi John,
            Thanks for the reply. I know you too know the answers to 
the questions I posed :)  I really meant (and should have made clear) 
that I was trying to encourage others (and particularly the 
speculators) on the list to actually get a scope onto it and see for 
themselves what happens. I hope as many as have access to 
instrumentation do.
     I'd just like to say that we are incredibly lucky in this day 
and age to have access to tools and instruments that Nikola could 
only have dreamed about. IMHO, full advantage should be taken of 
those tools to really understand how coils operate. Greg is not 
designing his new coil on pure but using a combination of measurement 
and advance in theory (hope you don't mind me speaking on your behalf 

     Thanks to my own experiments and an excellent post earlier this 
year by Gary Weaver ("The Best Primary"), I am now designing some 
experiments to examine coupling from a new angle. I have noticed that 
for resonators with an H/D significantly above 2, some height is 
required in the primary (i.e. a helix or saucer can work better than 
a properly tuned flat spiral). I came up with a guideline for good 
results that the height of a primary whose bottom turn starts at the 
same height as the bottom turn of the secondary  should be between
5 to 10% of the height of the secondary with a mean diameter around 
2 to 3 times that of the secondary. That was the experimental result.

    The theory: Using easily accessible mechanical analogy of the 
steel ruler in the vise and varying "coupling" height and noting 
effects on ruler movement, and looking at the concept of link 
coupling into a transmission line, it seems to me that what in effect 
we are doing is _tapping_ into the line at some way along its length
(this applies to 2 coil systems only). Now if you do this in a 
transmission line, you are tapping into a particular impedance (with
a particular impedance) since this is different along all portions of 
the line.

    Up to now, effects of coupling on coil behaviour have been rather 
difficult to determine. I think this is because when we normally vary 
k, we are varying at least two quantities at once! k can be varied in 
many different ways. For example, varying the height of the primary 
relative to the secondary is not only altering flux coupling but also 
the tap point. To alter k alone while leaving the tap point intact 
means increasing primary diameter while holding both primary height
and vertical position constant relative to the secondary. k can also 
be altered by reducing primary height and knocking a turn or two off 
to keep inductance constant. Another is to reduce turns and keep 
height constant while increasing Cp value to maintain tune.
    There is a good reason why this possibility has not been explored 
(as far as I know). Primaries are normally set in concrete as far as 
physical construction goes which makes it fiendishly difficult to 
change the diameter or the height at will.

   The experiments: I want to explore the possibility that altering k 
in different ways but just one parameter at a time will give 
credence to or refute the above ideas. It seems like a nightmare at 
first glance but I regard it as absolutely necessary to advance the 
art. If anyone has ideas on a construction method that might allow 
altering as few parameters as possible I would love to hear them. I 
am lucky to get use of the lab as such opportunites are fast 
disappearing here.

    Any other thoughts on the above most welcome. I regard tables as 
useful guidelines to building a coil, but nailing things down in 
mathematical formulae gives a much deeper understanding of how it 
works and in my opinion, puts design on an engineering platform.


> > (a) see whether you can quench a primary alone under single shot 
> > conditions (best of luck). Does your airblast noticeably affect the 
> > number of rings up to quench?
> Macolm,
> the quenching of my gaps also depend on successfully "draining" the
> energy from the system quuickly.  I suspect that my quenching would
> be miserable using a primary alone.  In general, I haven't had any luck
> with air blasts in conjunction with my sync-gap, but I still have to try
> the high volume method suggested by Dave Sharpe.
> > (b) set a system up to quench first notch under single shot conditions
> > and then progressively tighten coupling to the point where the quench 
> > no longer works to first notch. Compare this setting with that which 
> > you obtain with the air blower switched off. Is it the same for an 
> > attached spark as for an air streamer? What do the results say about
> > quenching affectiveness (yes, I think I already know the answers :)
> I've done the test for free air vs. attached streamers some time ago; the 
> quench moves from 1st notch to 2nd notch.  I can't remember if I used 
> a hard ground.  The gap can only accomplish so much, good quenching 
> depends greatly on obtaining reasonable impedance matching.  (I know
> you know all this   :)
> John Freau
> > Malcolm
>   >>