RE: Designing Primary Coil - Which resonant frequency??

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

Good question, I think I asked pretty much the same thing when I was
starting out.  It's almost a chicken or egg situation.

I think the best methodology is to start with the power supply size.  From
this one would determine the top load size and secondary size, based upon
what seems to work for others (there is unfortunately no formula for this),
and then work backwards to the primary.  Let's say a 6" x 24" toroid and a
6" x 28" secondary winding.

Now look at what kind of wire you have available for the secondary.
Calculate the secondary inductance and use Etesla-6 to calculate the
top-loaded secondary resonant frequency.  A variety of good programs
including Etesla-6 may be found on Terry's site at
http://hot-streamer-dot-com/TeslaCoils/Programs/Programs.htm.

Now consider the primary.  

A .01uF cap would be mains-resonant for a 15/60 NST, but this is not at all
a requirement.  With my 15/60 and a static gap, I've found that a .02uF cap
gives much better performance.  But a .01uF cap is OK if that's what you have.

Calculate the primary coil parameters needed to resonate with the loaded
secondary and your cap.  There are any number of programs that will do
this.  You need to make sure that you have a couple of turns left over for
tuning adjustments, and that the required number or turns is not too small
(say less than 6), or various inefficiencies will result, or too large that
it's physically impractical.  If the required number of turns is too small
or too great, you may need to adjust the secondary coil wire size to change
the frequency to something more appropriate for the primary to resonate
with.  As you can see, this may be an iterative process.

Regards, Gary Lau
MA, USA


 -----Original Message-----
From: 	Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent:	Sunday, July 07, 2002 12:13 AM
To:	tesla-at-pupman-dot-com
Subject:	Designing Primary Coil - Which resonant frequency??

Original poster: "Daniel McCauley by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

Another quick question regarding the design of the Primary Coil.

I've chosen my power supply and am using a 15kV, 60mA NST with calculated
output impedance of 250k ohms.
>From this my tank cap should be 0.0106uF.

My question is from everyone's experience, how should i go about designing
my primary coil?  Do i choose some arbitrary resonant frequency say between
100-200kHz from the tank circuit and then design the secondary coil to match
it or is there some "magic" resonant frequency i should try to meet.

Thanks again for the help!!!

BTW, my second-gen SSTC passed the first test with 360VAC input and the
results are spectacular.  Maybe tomorrow we'll move up to 480VAC,
half-rectified and see what happens.  See if those 1000V FETs can take
it!!!!

Dan