Re: 1st Tesla Coil

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

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

In a message dated 8/8/02 7:10:13 AM Pacific Daylight Time, tesla-at-pupman-dot-com
writes:


>
> Original poster: "quezacotl GF by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <quezacotl_14000000000000-at-yahoo-dot-com>
>
>
> Hi Everybody,
>
>          This is my first post to the mailing list and one of my buddies and
> I
> finished our first coil about a month ago. It took quite a while and with a
> bit
> of help (thanks Greg) we got it completed. The problem is that we can't draw
> anything from the coil without a grounding wire, and with it, we get all of
> the
> corona we want but actual sparks are thin, weak, 6-7" sparks. I'm asking the
> great and infinite wisdom of the tesla coil mailing list whether or not this
> is
> the best our coil can put out, or if there's something we can do. Here are
> the
> specs for the coil:
>
> Transformer: 12kV/30mA NST rated for 120 Volts. I am using the NST protection
> filter seen at
> <http://hot-streamer-dot-com/greg/filter.htm>http://hot-streamer-dot-com/greg/filter
> .htm
>
> Capacitor: 7 - 16oz saltwater bottles. We've tried 8 bottles but it didn't
> make
> much of a diffrence. ( I know MMTs are better, but I'm too poor to afford
> them.) 
>
> Spark gap: 7 - 3/4" copper pipes spaced about 1/16" apart. Gap can be widened
> or shortened if necessary.
>
> Primary coil: 15 turns of 1/4" copper refridgeration tubing spaced 1/4"
> apart.
>
> Secondary coil: approx 1080 turns of #26 gauge magnet wire. Coil is wrapped
> for
> 18.75" around a 3" diameter ABS pipe. Bottom of coil is connected to ground
> via
> a piece of rebar drove into the ground.
>
> Toroid: 4" cross section aluminum flex duct. Outer diameter is 15.25".
>
> If you have any questions, advice, comments, or just want to make fun of me
> for
> the fact that I can't build a Tesla Coil properly ( everybody else does )
> then
> just email me at
> <mailto:quezacotl_14000000000000-at-yahoo-dot-com>quezacotl_14000000000000-at-yahoo-dot-com
>
> Thanks, Chris




Chris,

I have some comments about your coil.  First off, you are correct, the coil
should be capable of generating sparks on the order of 12 to 20" in length. 
Your spark gap is a little wide.  My static gaps are usually set to about .020"
or .030" each and then I use 5 or 6 gaps.  If each of your gaps is .0625 and
you use all of them, your total gap would be .375" which I think might allow
the voltage to rise high enough to damage either your caps or the transformer. 
I did some calculations on your coil, making a few assumptions (one being that
the bottle caps would average about 900 pf each - this may be incorrect - for a
total primary cap of about .006 ufd) it should tune with the tap lead clear out
at the end of the primary, i.e. using all 14 turns.  I beleive the toroid is
quite a bit too big for the power level that you are running.  I would try
something smaller like 8" or 10" in diameter maybe by 2 or 3 inches high.  Then
you will ne! ed to move the primary tap in to account for the higher resonant
frequency.

Good luck, Ed Sonderman