Re: Help!!!, Building my first Coil Recomondations

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ArcStarter3-at-aol-dot-com>

Hey Raven, 

Welcome! I have a fairly good knowledge of Tesla Coils, so I may be able to 
help. 

>1. what safety chokes size do I need and where to order them from. 

By safety chokes, I assume you mean some sort of inductor, such as a coil, 
used to protect the NST from the RF in the primary circuit. When used in 
series with the outputs of the NST, the parasitic capacitance in the NST's 
windings will create oscillations that may actually be more harmful than the 
RF energy from the tank circuit. I would recommend using at least a safety 
gap across the outputs, and if possible, Terry Fritz's excellent RC filter, 
which can be found at 

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg 

Others will probably recommend this to you as well. 

>2. Now I need to know what size Commercial caps should I use, or if I go MMC 
>what size do I need. and how many? 
>and do I need to put a resister across each one. 

I would highly recommend using an MMC, or even an EMMC (Enhanced Multi Mini 
Cap), which just pushs the ratings of the cap a little to save money. You 
should probably talk to Terry Fritz about buying some 0.056 µF (microfarad) 
1600 VDC metallized polypropylene capacitors. These are perfect for Tesla 
Coil MMC's, as they are very low loss at high frequencies and can withstand a 
ton of abuse (for example, a test he ran indicated that these little 1600 
volt can withstand around 4000 volts before breaking down). 

As for the value of the capacitor, I would configure many of them in a 
series-parallel arrangement to vary the voltage ratings and capacitance. The 
resonant value of a tank capacitor for a 12/30 NST is 6.6 nF (nanofarad, or 
billionths of a farad), or 0.0066 µF (microfarad, millionths of a farad). I 
would suggest using a Larger Than Resonant (LTR) capacitor, as it keeps the 
caps from going over-voltage and causing damage to the NST, caps, etc. For a 
static gap, the LTR value is about 1.5x the resonant value, or 9.9 nF (0.0099 
µF). 

As for resistors across the caps, it is preferable as it balances out the 
voltage between caps and bleeds off any residual charge in less than 10 
seconds. A typical value for these resistors is 1/4 watt, 10 megohms (these 
are cheap, ~ 1 cent apiece). 

A capacitance of 11.2 nF (fairly close to 9.9 nF, and it wouldn't really do 
any harm, as it would just keep the voltage across the caps and NST lower) 
can be obtained by putting 2 strings of 10 caps in parallel (20 caps total). 
This would be pretty inexpensive. 

>3. How fare apart to I leave my spark gap? 

I wouldn't open up the gap any further than the maximum sparking distance for 
the NST alone (without cap, primary, etc.). To do would probably kill your 
NST and/or caps. To be on the safe side, I would leave the gap a little 
closer than that distance. 

>4. what size copper tube should I use for my Primary coil and how many turns. 

1/4" diameter soft copper refrigeration tubing is a typical conductor used 
for primary coils. This can be bought from a hardware store such as Home 
Depot in 50' lengths for about $15. As for how many turns, it really depends 
on the secondary coil parameters (mainly frequency). In general though, I 
would leave 1/4" or more between turns to reduce the risk of turn-turn 
flashover. The inner diameter of the primary coil should probably be around 
2" greater than the diameter of the secondary coil (ie, around 1" spacing 
from inner turn of primary to secondary). You should probably design the 
system around the secondary coil, IMO. How many turns is just what determines 
the frequency of the system, and you'd want the primary and secondary to be 
resonating at the same frequency for best results. There are several programs 
floating around on the internet that can be very helpful in designing a TC 
(WinTesla, for example). 

>5. What size PVC should I get and how tall should I go, recommendations 
please. 
& 
>6. What awg magnet wire should I get, and how many raps on the secondary and 
>how is it fastened to the PVC. 

I would recommend 4" - 6" diameter PVC for the coil form. In general, you 
probably want ~ 1600 turns on the secondary (John Freau's efficiency theory, 
he has a 12/30 system that throws 42" streamers) to allow for a higher 
primary inductance (more secondary turns = more primary turns), which would 
increase surge impedance (basically what determines how much current flows 
through the primary & spark gap), which, in turn, would reduce current 
through the spark gap and decrease losses. A height to diameter ratio of 4 - 
5:1 should work fairly well (ie, for a 4" diameter form, 16" - 20" winding 
height). BTW, the diameter of PVC is measured by the inner diameter, so a 4" 
dia. pipe may actually be 4.5" or more in dia. Find an AWG chart (I believe 
Terry Fritz has one on his website) and determine what wire size will give 
you the number of turns you want for the given coil height. 

>7. How large should I make the toroide? 

I just make the tube diameter about the same as the coil form diameter, and 
the outer diameter 3 - 4 times larger. 

>??On connections,  If some one wouldn't mind a phone call, so I can get some 
of 
>my more in-depth questions answered.  When I first started thinking  about a 
>Telsla Coil I thought oh just a little simple thing slap some wires together 
a 
>little transformer how hard can it be, What the Heck was I thinking. 
  
>I am just getting into this and I have been reading on this for about 3 
weeks, 
>I am still working all the math and terminology, kinda overwhelming at first. 

I know what you mean ;-) When I got into this about a year ago (i'm now 14), 
I had no idea it would be such a committment, and so far i've spent over $500 
(TC'ing isn't cheap!) and countless hours, and my parents are constantly 
thinking i'm going to blow up the house or something :-P BTW, should I 
mention that I don't even have a working Tesla Coil yet? :-) (broke my last 
7.5/30 NST and haven't gotten around to getting a new one, and my 15/60 is 
WAY too powerful for this system) 

>Thanks all the help I can get will be appreciated. 

I hope this was of some help. I find that this list is an excellent source of 
information, and has answered many of my questions throughout my time here. 
If you can find someone that lives near you that has a Tesla Coil and may be 
of some help, that would probably help you a lot. I wouldn't mind answering 
some Q's over the phone, just got to get my parents to let me call 
long-distance ;-). Or if you live in or near Denver, it wouldn't be a 
problem. Good luck! 

Regards, 

Josh Hunsaker 
---------------------- 
Denver, Colorado 
ArcStarter3-at-aol-dot-com