Re: primary field

To: tesla-at-pupman-dot-com
Subject: Re: primary field
From: Bert Hickman <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Thu, 03 Sep 1998 19:26:55 -0600
Approved: terryf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: "chris.swinson" <chris.swinson-at-zetnet.co.uk>
> 
> I'm still confused about the fieled for the primary.
> 
> Someone said that only the first few inches of the secondary are coupled to
> the primary.  This seams to me not to be true as the field is 40" high and
> my secondary is 36" high, so it does not seam right.  By that, I could build
> a coil twice as high and just have half the coil coupled.
> 
> Can anyone tell me how "big" the fieled is and the coupling strength from
> primary to secondary ?
> 
> All the beST,
> Chris.
> 
> chris.swinson-at-zetnet.co.uk
> www.users.globalnet.co.uk/~mega01/    <--- moved site to...
> www.users.zetnet.co.uk/mega.disczine/

Chris,

There's really no sharp boundary where the IS or ISN'T a field. The
important relationship is that portion of the total primary magnetic
field lines that are _shared_ (or common) between the primary and the
secondary. This factor is called the coefficient of coupling or "k". Now
"k" can have any value from 0 (no coupling) to 1.00 (perfect coupling),
and it's purely a function of the primary and secondary coil geometries
and the distance between them. 

For a variety of theoretical and practical reasons, spark-gap driven
Tesla Coils perform best with a "k" in the range of 10-25%. A post
yesterday by Terry Fritz [coupling coefficient - Best Method] covered
how to measure the "k" quite accurately. 

-- Bert --