Re: [TCML] New 3.5" Coil - A kick in the right direction please!

[G Hunter <dogbrain_39560@xxxxxxxxx>]

Hmmm...sounds like information overload syndrome complicated by excessive advice.

Spark gap Tesla coils are not very complicated.  Almost any screwed-up piece of junk will make sparks--I should know!  An "optimized" coil requires a bit more care, of course, but there's still plenty of wiggle room in the design specs.

Start with the secondary.  H:D ratio should be approximately 4.5-to-1, but that's only a guideline.  For your 3.5" diameter form, Any length from 12" to 18" will do.  Choose a wire diameter that will give you about 1000 turns on your coil form.  Again, anything from 800 to 1600 turns will do.  Don't worry about the operating frequency.  There's no "best" frequency that I'm aware of.  I've run coils at over 500kHz before.  They worked pretty good.  There's nothing magical about 220KHz.

Never mind the 1/4 wave jazz.  Your finished secondary coil will have a fundamental resonant frequency based on it's lumped inductance and distributed capacitance.  Top-load capacitance will push that frequency downward a bit.  The exact length of the wire is immaterial.  The correct length of wire is that length of wire which will fill up your coil form.

For NST-powered systems, slightly larger-than-resonant tank caps work well.  Aim for 1.2 to 1.5 times the resonant cap value.  Now calculate the number of primary turns required to get in tune with said cap.  Give yourself a safety margin of at least 2 or 3 extra turns.  Don't worry about the relationship between primary coil diameter and secondary coil length.  It isn't that critical.  If you want to stress over detail, then worry about primary/secondary coefficient of coupling--a parameter that actually matters!

Likewise, there's no "correct" number of primary turns.  The "best" number of turns is however many it takes to make your coil work.  I've never heard of a 9 to 12 turn boundary.  If your coil tunes up at 3 turns, or at 23 turns, then so be it.

Cheers,

Greg

--- On Fri, 9/19/08, Grant Visser <freeekyg@xxxxxxxxx> wrote:

> From: Grant Visser <freeekyg@xxxxxxxxx>
> Subject: [TCML] New 3.5" Coil - A kick in the right direction please!
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Friday, September 19, 2008, 2:48 AM
> Hi there,
> 
> Suffering from sleep deprivation or 18 hour research / calc
> / sim /
> research .... info overload at the moment, or BOTH! lol
> 
> With my limited budget I am on a mission to get a solid
> base design
> into my head before I begin throwing things together as I
> did last
> time! *grin*
> 
> The problem is that I have now done so much reading of
> content from so
> many different viewpoints (over the years) that I have
> confused myself
> COMPLETELY! Thus, I humbly beg your assistance ... or at
> least just a
> darn good kick in the right direction!
> 
> I have in front of me 26.06" of 3.543" Plexiglass
> tubing with 3mm
> (0.1181") wall thickness (and don't want to waste
> a single mm of it!)
> lol
> Assuming 220V 50Hz mains and 2x 9KV/40mA NST's to power
> my new
> coil(/s) (could add another 2 very soon!!!)
> 3Kg of Double insulated magnet wire about to be ordered, ex
> works in
> either 0.335mm (0.013188"), 0.355mm (0.013976"),
> 0.375mm (0.014763"),
> or 0.4mm (0.015748") OD
> Have tried my best but am not going to be able to afford
> the (less
> than ideal) caps for a solid MMC so have decided that I
> will build a
> quality bank of vertical plate caps for this coil.
> They'll never go to
> waste!
> I have also decided (I think) to go for a balanced split
> cap tank design.
> Until I can find a decent blower I'll be using my
> current suction
> quenched adjustable 2 gap design.
> 1/4" copper tubing for the flat pancake primary coil
> Oh, and yes I do now have a SOLID and dedicated RF Ground.
> I do also have 3phase at my disposal .......
> 
> Although it didn't even cross my mind initially, one of
> my biggest
> stumbling blocks at this point is at what frequency I am
> going to run
> this coil. This quandry started when I read a few posts
> from awhile
> back regarding the primary winding and that it should have
> no less
> than 12 to 15 turns and tuned at no less than 9 turns, and
> ensuring
> that the final diameter or the primary is the same or close
> to the
> winding height of the secondary! Apart from the fact that
> it actually
> made sense to me from a coupling point of view, it also
> meant that I'd
> be able to use a smaller main cap, so I was very happy
> right up until
> I started doing the math / sims and it meant that I was
> going to have
> to use a "SMALLER THAN RESONATE" capacitor which,
> seems to be an
> absolute no no if I have understood the numerous other
> posts and
> articles I have been reading!
> 
> A further brainmangler that has crept in now is the other
> concept that
> I had forgotten about ..... and that is that I would want
> to design my
> secondary to have the length of wire I need to resonate
> with my
> primary at a 1/4 wave! ie. At 220KHz the 1/4 wave is at
> 1118.1818ft
> and I should thus use exactly that length of wire to coil
> my
> secondary. Again this all makes perfect sense ....... right
> up until I
> start doing the math and the sims ....... at which point,
> depending on
> which program I use to model my coil, either the program
> yells insults
> at me, or I simply cannot find a workable solution which
> allows me to
> use all of the data above AND have a resonate coil with a
> decent hd
> ratio! Going much below 220KHz means that I would have to
> increase the
> length of my coiling wire to seemingly crazy HD
> ratio's!
> 
> Now I do absolutely want to achieve the longest possible
> sparks from
> this coil and I would like it to be an unstressed system
> allowing long
> run times. I would also however like to use this coil to
> begin
> demonstrating and researching the concepts of powering up
> light bulbs
> etc from the ground waves for which I am going to have to
> construct a
> top load with no breakout! With this in mind I was hoping
> to either
> split the 26" form in half allowing me to coil two
> seperate identical
> secondaries and use the second in a magnifier
> configuration. OR .... I
> was even considering (but had not yet begun much research)
> using the
> form for a BIPOLAR coil!
> 
> I do realise that 3.5" is not exactly a MEGA COIL but
> it did seem to
> me that it could be a nice little testbed to get me started
> with some
> of the more interesting experiments! ???
> 
> SO! Thats where I stand at this point! More confused than
> ever and
> really hoping that you will be able to help me back onto
> the straight
> and SPARKY!
> 
> Grant Visser
> Randburg, South Africa
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla


      
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla