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

[Scott Bogard <sdbogard@xxxxxxxxx>]

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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