Re: Primary coil idea

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

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.  
    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...
 
 
 
 
  >>