Re: [TCML] Secondary Coil: Wire Gauge and Number of Turns

[Atomic <atomicrox@xxxxxxxxx>]

How can the current be larger on the bottom of the secondary if it's just a
continuous wire? Shouldn't the amps flowing on the bottom be the the same
amps going to the topload?

On Tue, Jul 2, 2013 at 12:51 PM, David Thomson <
tcbuilder@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hi Brandon, you may want to change your strategy in your search for coil
> efficiency.  I have had very good results by using a combination flat
> spiral and solenoid secondary.  I suspect the best geometry would be a horn
> shape with the large diameter of the horn in mutual inductance with the
> primary and the tall skinny solenoid end approaching the top load.
>
> The theory behind this design of a secondary is that the primary side of
> the secondary coil has a greater current running through it whereas the top
> load side of the secondary has a greater potential running through it.  The
> current side of the secondary works best when the windings are nearly flat
> and wound inside each other and the potential side of the secondary throws
> the greatest potential when the secondary windings are stacked on top of
> each other. The horn geometry allows for the morphing from a flat spiral
> coil to a tall skinny solenoid coil.
>
> Since the horn geometry has maximized current in the ground side and
> maximized potential in the top load side, the coil form will then hold the
> maximum amount of power for a given amount of copper.
>
> To further maximize the coil design, a larger gauge of wire should be used
> in the large diameter windings and a finer gauge wire should be used in the
> smaller diameter windings.  Tesla used this general concept in his
> Wardenclyffe oscillator.  He further found that the top load can be
> suspended a great distance above the secondary and connected by a solid
> metal shaft.  The reason for this is because as potential rises near the
> top of the secondary the windings behave as a solid pipe, rather than
> separate windings.
>
> I can post more information on the specifics of the coil form if you are
> interested.
>
> Dave
>
>
> On Tue, Jul 2, 2013 at 7:00 AM, Scott Bogard <sdbogard@xxxxxxxxx> wrote:
>
> > Hi Brandon,
> >      I'm curious where you heard that a higher inductance is better?  It
> > blatantly isn't, any more than blue is better than red, as the single
> most
> > important thing is balance of the components.  With that said, to answer
> > your question, what do you hope to achieve out of this coil?  Big sparks?
> >  Power handling capability?  Highest possible voltage?  Aesthetically
> > pleasing?  Wireless power?  These are what is going to dictate your
> design,
> > not "biggest inductance".  For the biggest sparks, we have found about
> 1200
> > turns and 4.5/1 height to diameter to be optimal.  This is based largely
> > off of experimentation, higher turns have been used quite successfully,
> but
> > 1200 is enough to make you rip your hair out, why go higher?  If your
> > purpose is to experiment, and try something new, by all means, use your
> > design, as long as it is tunable from a frequency and power draw
> > standpoint, I see no reason not to (my first coil had only 400 turns, and
> > it worked pretty decently.)  As a point of interest, if you are trying to
> > maximize inductance for a given piece of wire there are posts about this
> in
> > the archives, if memory serves (which it may not) a very short 0.3/1 H
> to D
> > ratio was best from that standpoint (wider than tall).  The problem with
> > that obviously is that primary strikes will almost certainly be
> > uncontrollable, this doesn't mean you cannot play with it though!
> >      Given you are still in the design phase let me tell you how I would
> > approach it, assuming you were going for maximum spark length and
> > aesthetically pleasing as primary design motivators.  You know you will
> be
> > using 1,825 watts, so we back calc for spark length and get 72 inches, so
> > we pick our secondary length at 72/2.5= 28 in (a good size from a power
> > handling standpoint, but optimally nice and compact (pretty) and easy to
> > build.)  From there plug into Tesla map and find your wire gauge for 1200
> > turns, try not to fall in love with a gauge before hand, it is just
> > arbitrary, one is not better than the other except that it fits your
> > design.  Then go from there, size the cap to suit your gap BPS, and size
> > your primary to suite your cap.  It is just how I go about choosing
> > variables, as you pick them in an order so you don't have to go back and
> > re-size anything.  At any rate, let us know how your project turns out,
> and
> > what you decide to do, if you go the higher inductance route it will be
> > interesting to see what it does to the spark behavior!
> >
> > Scott Bogard.
> >
> >
> > On Mon, Jul 1, 2013 at 5:12 PM, Brandon Hendershot <
> > brandonhendershot@xxxxxxxxx> wrote:
> >
> > > I've been punching numbers into TeslaMap for a while trying to design
> my
> > > next secondary coil. I know the idea is to get the Inductance as high
> as
> > > possible, but the conflict with that is ending up with more and more
> > turns
> > > as you raise the inductance. I know that the AC resistance of the wire
> is
> > > going to be a bigger issue with more turns. Acceptable values I've
> heard
> > > are 1000-1500 turns.
> > >
> > > How critical is this range? My designs tend to come out with 1650-1800
> > > turns.
> > >
> > > Another factor in design is the wire gauge. The thinner the wire, the
> > more
> > > energy is lost to resistance according to Ohm's law. The thinner wire
> > also
> > > allows the inductance to be higher given a limited winding height. I'm
> > > really not sure which way to lean in balancing that out... More
> > inductance
> > > vs more resistance (I suppose the power put into the coil helps
> > determine a
> > > minimum).
> > >
> > > I'm hoping to build with 27 or 28 gauge magnet wire
> > >
> > > Coil is running 1825 Watts (15/120 NSTs), 120 BPS SRSG, 0.25 x 0.25 x
> 14
> > > turn primary (7.5" Hole), 55nf Tank Cap
> > >
> > > (Some of my design parameters: Stick close to a 4:1 ratio, 6.1-6.6"
> > Width,
> > > 24-29" Height, while keeping the required primary inductance to about
> 90%
> > > of the primary coil's capacity.)
> > >
> > > Hope you can help. Thanks!
> > >
> > > - Brandon H.
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