Re: More Coupling...

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <paul-at-abelian.demon.co.uk>

Concerning Bart Anderson's coupling coefficient, I wrote:

>> p-s
>> (cm)    k
>> -3     0.156
>> -2     0.163
>> -1     0.171
>>  0     0.178
>>  1     0.186
>>  2     0.194
>>  3     0.201
>>  4     0.208
>>  5     0.215
>>
>> Bart, I'd like to know the height of your primary wrt the secondary
>> base (p-s) at which your measurement was made.

Barton B. Anderson wrote:
 
> My secondary was elevated 1.5" above the primary as measured from
> the primary inner turn to the first secondary turn. That's about
> 4cm, isn't it.

Yes, unfortunately 4cm the wrong way. Thats possibly bad news for
acmi, although with the primary sitting below the secondary like that
I have to share Ed Phillips' surprise that the k is so high. The
predicted k of 0.208 occurs when the primary is 4cm above the start
of the secondary, a point 8 cm higher up than your given position.

> I find the graph and above data interesting in that as the distance
> (height of s to p) is increased, the k value increases?

I'm taking p-s as the height of the plane of the primary above the
start of the secondary winding. Your secondary at 1.5" above the
primary corresponds to a p-s of -4 cm in my data. Positive values of
p-s occur when the secondary is lowered inside the primary.

> I've always thought that lowering the secondary decreases
> coupling?

Lowering the secondary into the primary must increase the coupling
since the fields of the two coils overlap to a greater extent.

> From your data, it appears just the opposite. If this is true,
> then we need to invert our ideas about coupling and racing sparks
> phenomenon.

I doubt anything radical is emerging here. We just need to clarify our
definitions of winding separation I think.

      |         |
      |         |
      |         |
      |         |
      |         |
----  |         | ----        <--   
      |         |               |  My positive p-s distance.
      |         |             <--


      |         |
      |         |
      |         |
      |         |
      |         |
      |         |
      |         |             <--
                                |  My negative p-s distance.
----              ----        <--   

Your primary is below the start of the secondary, ie a negative 4cm
p-s, corresponding to a predicted k of 0.149, against your reported
0.205, quite a large discrepancy which I'd like to try to resolve.

Bart, could you check that my predicted 80.3 mH and 109 uH for
secondary and primary respectively match your inductance measurements?

Cheers,
--
Paul Nicholson,
Manchester, UK.
--