Re: Primary coil idea

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi all,
        A note on this "splitting" issue:

On 13 Jul 01, at 12:35, Tesla list wrote:

> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Hollmike-at-aol-dot-com>
> 
> Hi Pete,
>     What you are saying would be workable, but you must keep a couple of 
> things in mind.  First, the coupling between the coils needs to be 
> loose(around 0.2 for the coupling coefficient).  What you are suggesting 
> could easily lead to overcoupling which will cause two frequencies to be 
> generated on the secondary(which are equally displaced on either side of the 
> actual resonant frequency of the coil).  The problem with this is that 
> constructive/destructive intereference will occur and cause spots of high 
> voltage to appear at locations below the top of the coil.  I think the hot 
> spots will actually travel up and down the secondary at a rate equal to the 
> difference between the two frequencies assuming it doesn't burn up the 
> windings on the first pass.  This is why most people simply use a flat
spiral 
> primary.  

*All* disruptive coils produce "frequency splitting", guaranteed. It 
is an inevitable consequence of the act of running the primary down 
while running the secondary up. The sidebands exist because the 
amplitude of the waveforms is changing continuously. You can see 
whether a coil is going to do this or not by feeding a *high* 
impedance sig gen across the primary *with the gap shorted* and 
monitoring the secondary e-field with an aerial scope probe. You will 
find there are *two* resonant peaks, not one and  neither is the 
resonant frequency of your primary or secondary as measured on its 
own. If it doesn't do this, then you will not get the system to 
produce sparks.

Regards,
Malcolm



>     Another problem to consider is that if you use a small clearance between 
> the primary and secondary, is that you will have to provide adequate 
> insulation between the coils to prevent flashovers.  This can pose quite a 
> challenge.  Again,  this is a good reason to stick with a flat spiral
primary.
> Mike
> 
>    
> 
> 
> << Imagine two series helical primary coils.  An inner coil wound on 6" PVC
>  using #12 THHN insulated wire(about 7 turns per inch).  An outer coil wound
>  on 8" PVC using #12 bare wire with enough spacing between winds to allow
>  tapping and air insulation.
>  
>  Or an inner tight wound helical with an outer spiral wound part for
>  adjustability.
>  
>  Wouldn't some variation of this work and be a lot more compact than the
>  usual spiral primary?
>  
>  Is the magnetic field more compact with a smaller coil (same inductance with
>  smaller area)?
>  
>  Is there any advantage or disadvantage to larger or smaller (in area)
>  primary coils?
>  
>  Regards,
>  
>  Pete Komen
>  
>  I have lots of ideas and things to try, I just need more time...more
>  money...more space...
>  
>  
>  
>  
>   >>
> 
> 
> 
>