Re: My First Tesla Coil

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

Original poster: Esondrmn-at-aol-dot-com 

In a message dated 5/13/04 3:51:49 PM Pacific Daylight Time, 
tesla-at-pupman-dot-com writes:

Chris,

These are my opinions, you will probably get several.  Approximately 1200 
turns on the secondary is what you want.  If you have # 27 wire, you should 
measure the diameter and calculate the winding length required.  My wire 
chart says # 27 is nominal .0152" in dia. up to .0164" for heavy build 
insulation.  That is a range of 65.8 to 61 turns per inch.  For 1200 turns 
this would be a winding length of about 19".  Using a 4" diameter secondary 
would yield a 4.75:1 ratio which is good.   You want to be in the range of 
4.5:1 to 5.0:1.  For a coil of this size, I would suggest a flat primary of 
.25" copper tubing with an inside diameter of 6.0" to 6.5", .375" between 
turns and 12 to 15 turns total.  There is no special turns ratio you are 
looking for here.  The self resonant frequency of the secondary coil with 
toroid and the self resonant frequency of the primary coil with primary cap 
must match.  A capacitor value is selected so the coils will be in tune 
when tapped at about 80% of full turns on the primary.

Mylar caps are very lossy and usuall fail quickly in Tesla coil use.  You 
want to build a cap with individual caps (mmc), or buy a good commercial 
pulse cap (expensive), or build you own with aluminum plates and LDPE (low 
density polyethylene) or make some salt water caps.

Have fun.

Ed Sonderman


>Original poster: "Chris Fanjoy" <zappyman-at-hotmail-dot-com>
>
>    I've wanted to build one of these for several years now, but just never
>got around to it. But finally, I'm now ready to build my first coil!
>Although I have spent years in electronics (mostly repairing TV's etc), the
>principles involved in Tesla coils are still not completely within my
>grasp. That's why I'm asking for your help.
>    I received the main ingredient in the mail today - a 10 lb spool of #27
>AWG magnet wire. Upon seeing the immense size of the spool, I now realize
>that I have more wire than I'll probably ever need! Not a problem though,
>since an associate of mine also wishes to build a coil, and I'll probably
>just share some with him. As for the other materials - high voltage
>transformers, capacitors, large-diameter copper wire, etc - I have a large
>stock of these items that I've collected, from the years I've spent
>repairing consumer electronics.
>    I've got quite a mouthful of questions, but I'll try to summarize them
>as briefly as possible:
>
>Consideration #1 : Number of coil turns / turns ratio
>
>    Most info I've collected from the web, suggests winding about 2-4
>thousand turns of 20-24 AWG magnet wire, for the secondary of the coil. The
>primary should be about 20-25 turns of heavier (<14 AWG) copper wire. Is it
>theoretically possible, to use a turns radio of 1:100 (say, primary=10
>turns and secondary =1000 turns), to multiply the input voltage by 100x?
>(assuming 100% efficiency, obviously it will be much lower in real life).
>Secondly, how does one determine the proper number of turns? And finally,
>can the primary and secondary windings be isolated from each other by
>putting a larger-diameter piece of PVC pipe between them? (to prevent arcing)
>
>Consideration #2 : High Voltage Transformer
>
>    Since I have literally dozens of old MOT's in my parts pile, it goes
>without saying that this will be what I use. My first question is, are the
>older (bigger) ones better? Size might be a consideration depending on the
>enclosure I built this stuff into. And also, is it possible to use two
>transformers (primaries wired in parallel, secondaries in series) in order
>to get twice as much voltage to feed to the spark gap/capacitor? Since two
>MOT's would draw more than 15 amps from the wall, some kind of current
>limiting would be needed (custom-wound inductor?)
>
>Consideration #3 : Tank Capacitor
>
>    It seems that everyone uses a tank cap comprised of dozens, or hundreds,
>of small HV caps to get the required value and voltage. I have a fair
>number of mylar caps (mostly from 70's and 80's color TV's) which may do
>the job, but I'm wondering if microwave oven capacitors would work. I have
>dozens of em', and most have values of 0.7 - 1.0 uF at up to 2400VAC -
>each! Only thing is, they have bleeder resistors (typically 10meg-ohms
>each) and might not withstand high operationg frequencies. And what about
>high-voltage ceramic capacitors, are these any good?
>
>    Maybe that's enough questions for now. It will take some time to
>assemble all the components, and work out the design. I look forward to any
>advice you may have.