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Re: [TCML] Secondary Coil: Wire Gauge and Number of Turns
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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> > Tesla@xxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
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