Re: Primary Thoughts

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

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

Hi Ray,

On 3 Apr 01, at 17:46, Tesla list wrote:

> Original poster: "Ray Robidoux by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <robidoux-at-basystems-dot-com>
> 
> Hi All,
> 
> I was musing about primaries on my long commute
> home one day. My current TC is a 2.5" x 13" with
> a 45 degree conical primary using 1/4" refer pipe.
> The Primary is tapped at turn 10 out of 13 turns.
> So I got to wondering just what those extra turns
> are doing electrically to the TC circuit. They
> would seem to resemble an auto-transformer if
> looked at schematically:
> 
>  To the CapPrim______
>                      )
>                      )
>                      )   Lprim
>                      )
>  To the Spark G______)
>                      )
>                      )   Lextra
>                      )
>  Floating_end   -----
> 
> But because the "Floating_end" 'floats' there is "no"
> current flow in Lextra so maybe it does not contribute
> to the circuit of the TC. But wait, it is an inductor
> immersed in a magnetic field, just like the secondary,
> so it must have some effect. So the question is not does
> it have an effect, but rather is this effect positive or
> negative with regard to spark length. So I thought about
> an experiment to find if Lextra can be used to help in a TC.
> What would happen if I were to put a Cap in parallel with
> Lextra (CapExtra) such that:
> 
>                   CapPrim x Lprim  ==  CapExtra x Lextra
> 
> Then I would have another tank circuit at the same resonance
> as the Primary tank, that might increase energy delivered to
> the secondary.

Good expts. Adding the extra capacitance detunes the primary. It is 
an autotransformer and if left open circuit, shouldn't have any 
effect. 

> So when I got home I tried it right away. But what I found
> was that I suddenly had NO output from my secondary. :(
> Obviously the Lextra part of this arrangement is directly
> opposite in phase as the Lprim tank. To further verify what
> is going on, I tried a different Cap value that would not
> be at the same resonance. And when I powered up I was getting
> sparks of about the same length as my TC would normally give. :)
> 
> So I concluded that the Lextra CAN effect the output of a TC.

It will if you load it with something of course.

> But the question remains as to how much does it detract from
> spark length (if at all). One thought to test this would be
> to design a primary that can be added to in stages. Then one
> could make the primary just the exact length for proper tuning
> and no longer, measure the spark length. And then add several
> extra turns on the primary and measure again. This sounds like
> a job for a flat spiral, because the form to hold this primary
> would accommodate such a modular primary without too much trouble.
> 
> Like all of us I am busy and would have to add this to the bottom of a
> very long to-do list. If anyone out there is willing to spend some
> time and would be able to go on with this idea, I for one would be
> curious as to the outcome. After all we all put extra turns on our
> primaries "just in case". Well if they are detracting from our main
> goal (BIG SPARKS) then lets rethink this a little.
> 
> Looking forward to all comments:
> Ray.

I've run a number of coils both with and without extra primary turns. 
I don't see any effects detrimental or otherwise.

Regards,
malcolm