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Re: Re: Big Primaries, Small Caps

You know, I am curious about something, since you are on this subject
about big primaries.  I have my 3/8" copper refrig. tube primary tuned at
the 7th loop from the center, and it has a total of 14 turns in all.  It
seems the more doorknob caps I add to the tank circuit, that the less
primary coil I need to tune my 8" secondary for maximum spark.  But what
I am trying to get at is this,  do I really need the unused outer turns
of the primary as I increase the efficiency of my coil.  Do the unused
outer turns contribute anything to the circuit?  A small thick primary
would take less space.  But before I cut it off, say at about nine turns
I would like to know if anyone has removed unused turns from their
primaries with any ill effects?  I do remember when I first started
coiling and used bottle caps, that I needed  as much primary coil as I
could get.  I even added on a length of tube just to get the coil to fire
and ran the coil  tapped at the very last outermost turn.  But as I added
bottle caps, it seemed I needed less primary winding, and the doorknob
caps needed even less primary tubing.  So, do we really need all that
unused tube once we get our coils tuned and running? I am looking for a
smaller, lighter package with max spark in a yet to be built future coil.

On Sun, 03 Sep 2000 16:58:28 -0600 "Tesla list" <tesla-at-pupman-dot-com>
> Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> 
> Hi Greg, 
> Tesla list wrote: 
> >
> > Original poster: "Gregory R. Hunter" <ghunter-at-accucomm-dot-net> 
> >
> > Dear List, 
> >
> > I'm curious about Tesla coils with large primaries and small tank 
> caps. 
> > John Freau and others have articulated numerous times over the 
> years that 
> > coils so designed have lower gap losses and longer sparks relative 
> to coils 
> > using big tank caps and few primary turns.  I'm curious as to why 
> this is 
> > so.  It seems to me that the bigger bang size delivered by a 
> larger cap 
> > would thump the secondary harder, yielding longer sparks.
> With a static cap value (regardless of value), more turns on the 
> primary
> reduces losses because more turns equates to a higher impedance (due 
> to the
> added inductance). The higher impedance reduces the current. Reduced 
> current
> (at gap conduction) reduces I^2R losses. Reduced losses equates to 
> better
> efficiency. Better efficiency equates to longer spark lengths for 
> the power
> input. 
> With larger cap values (regardless of pirmary turns): due to the 
> increased
> joules, there will be higher losses at the gap due to the increased 
> current.
> The inductance at the primary will either reduce or increase the 
> losses for the
> cap energy depending on how much inductance is used, but still, a 
> larger cap
> value will probably have higher losses than a smaller cap value 
> used. I've run
> 20nF, 40nF, and 60nF with the same coil. Spark length did not 
> increase
> linearly. It did increase with increased cap energy, but at a 
> fraction of the
> spark length, and with less efficiency. 
> A couple years ago, I added 12" of length to my secondary (was 34"L, 
> now 45"L).
> This caused more turns for the secondary and more turns on the 
> primary. I
> gained about 15" of spark length simply due to this change. Still, 
> there are
> gap losses. I later built a G10/tungsten RSG. This gap was much 
> better than the
> previous versions "because" I gained approximately 10" of spark! The 
> gap was
> more efficient and it was very clear to me that the gap itself made 
> a
> tremendous difference regardless of cap size or primary turns. To 
> this day, I
> realize that gap losses are significant and more primary turns helps 
> reduce
> these losses. 
> But still, there are losses and the losses can increase with cap 
> size. I think
> it is possible to build a coil that can run a large cap size and be 
> efficient,
> but the coil must be designed to reduce losses at the gap. This 
> means gap
> design, primary turns high, low Fo, properely sized toroid, etc.. 
> John Freau and Malcolm Watts are two coilers that have helped 
> identify "why" my
> coil reacted to the changes with the increased turns on the 
> secondary. Ed
> Wingate believed in pure tungsten electrodes and G10 for a rotary 
> gap which I
> built and I was amazed at the efficiency of the gap compared to the 
> copper
> electrodes or spinning pipes (remember that one?) I tried previous 
> to this. The
> previous gaps were poorly designed. Now, if I used copper electrodes 
> with the
> G-10 I would probably run just as efficient as I am now, but the 
> tungsten life
> is far superior. My previous copper electrode RSG used an alluminum 
> flywheel
> (crap-gap). 
> I've also run variable RSG speed (DC RSG), non-sync, and sync gaps. 
> They all
> have their good and bad points with the non-sync being the worse 
> (IMHO). I use
> a sync gap currently simply due to the ability to keep the gap at a 
> steady
> state for whatever test I am running at the time (it helps remove a 
> variable).
> I really liked the DC gap because it's easy to find a break rate 
> that the
> system enjoys, but for testing purposes, it throws in a factor that 
> prevents
> comparisons between setups. 
> Take care, (sorry to ramble) 
> Bart 
> >
> >   
> > Can someone in the know provide an explanation?  I'm not an 
> engineer, but I 
> > am an experienced comm/nav technician, so I can grasp pretty deep 
> concepts. 
> >  However, a side trip into Calculus land will lose me pretty 
> quickly. 
> >
> > Best Regards, 
> >
> > Gregory R. Hunter