Re: 1st Tesla Coil

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Chris,

Just a couple comments.
First, I don't think there's anything wrong with your gap spacing.
The total gap spacing is 0.375" and the OD of the pipes are 0.75". If you are
applying 120V at the transformer input, your output is 21.2kVp. The gap should
conduct at near 21kVp (and is where you want to be). I'd say the gap
"distance" is
fine for now.

The tuning is probably the area to doublecheck at this point. Unless you have
measured the caps, the tuning could be outside the primary turns (or in).
So, find a
meter and measure those caps. If a meter is hard to come by, you can still do a
couple things:

1) Get some scrap wire and wind a few more turns to the primary (just for test
purposes) to see if it tunes further out. If so, you can easily replace it.
Once you
**know** it's tuned the best it can be, you can easily back calculate the
cap size
for future reference. If the caps are 0.006uF, the tune point should be
around 12 or
13 turns which accounts for about 20% resonator capacitance decrease due to the
toroid size.

2) Another approach is to make up a couple more bottles and add one at a
time to
look for a difference and adjust for max arc length (more capacitance will
reduce
the number of turns required to meet the secondary resonant frequency).
Leave the
tap at the full primary turns.

3) Simply tune "in" to check the other end of the spectrum (you've most likely
already gone this route).

When you check tuning, add a breakout point on the toroid (punch a nail
through a
piece of tape and stick it to the outer edge of the toroid about 1/2" above
horizontal center). You might also want to attract the spark with an RF
grounded
wire near the nail. Find out the distance it will arc, then increase the
distance an
inch or so and try the above tuning techniques to reach the nail. Continue
moving
the RFgnd wire further away until your sure you are acheiving max distance.
This
isn't necessarily max arc distance, but it "will" get you tuned.

Take care,
Bart

Tesla list wrote:

> 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