Re: 5 Turn Primary?

["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>

I must have brainlocked:

On 21 Mar 01, at 19:05, Tesla list wrote:

> Original poster: "Malcolm Watts by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> Hi Nate (and any beginners):
> 
> On 21 Mar 01, at 8:11, Tesla list wrote:
> 
> > Original poster: "Nathan Morris by way of Terry Fritz
> > <twftesla-at-uswest-dot-net>" <themfam-at-home-dot-com>
> > 
> > Question,
> > 
> > If the cap value can be changed so that the number of primary turns
> > is reduced, then my question is, how do you know when to stop?  With
> > the right cap value the primary could be limited to just a few
> > turns. There has to be some loss of efficiency as some point.  What
> > is a good rule of thumb for knowing where to plan ones primary tap? 
> > I currently have over twenty turns and I am planning on cutting that
> > back to about 16 turns.  I have 40 good HV (10-30 KV ) caps on the
> > way so I am flexible with my cap configuration.  I would like to
> > reduce the physical size of my primary as much as possible without
> > jeopardizing performance.  
> 
> It is not the turns that count - it is the inductance. There is an
> infinite number of coils that can be wound with 16 turns, 5 turns,
> whatever, all with different inductances. There is no ideal number of
> turns. Any reduction in primary inductance is accompanied by a
> progressive loss of efficiency if the primary capacitor is kept the
> same. Doing this implies a reduction in either secondary C or L or
> both to maintain tune.

This bit:

 You can usefully boost the efficiency of your
> coil by decreasing primary inductance (Lp) and increasing primary
> capacitance (Cp) but you must also increase primary voltage (gap
> spacing - Vp) to maintain the same primary bang energy (Ep). 

..... by *increasing* primary inductance and *decreasing* primary 
capacitance........

Hopefully I've forestalled getting jumped on. Sorry.

Malcolm

>       Note also that reducing primary inductance (turns
if you really
> must) is _generally_ accompanied by a reduction in the coupling
> constant (k) so the primary must be brought closer to the secondary 
> if k is to be maintained. 
>       The upshot is: you cannot reduce Lp and maintain the same 
> efficiency if nothing about your secondary coil changes. You may find
> that lopping a couple of turns off the primary and reducing Ctop
> doesn't affect performance to a huge degree but only you can know
> whether the degradation is acceptable to you or not.
>       Finally, I think some of the questions many people ask are best
> answered by a good ol' bit of DIY experimenting. That is exactly how
> most people on the list who are capable of answering your questions
> learnt it for themselves. To the world in general: it doesn't take
> much imagination to figure out how to wind a coil.
> 
> Malcolm
> 
> 
> 
>