Re: My second coil attempt, advice?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Mddeming@xxxxxxx 

Hi Scott,

Comments interspersed.

In a message dated 3/14/07 12:15:06 A.M. Eastern Standard Time, 
tesla@xxxxxxxxxx writes:
Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx>

Hello all,
     I am a relative newbie to the list, and I have recently finished
my second Tesla coil (60Hz AC system), and the output is Ok (strikes
38 in, and streamers about 5 ft tops) but I have seen very similar
coils put out as much as 8 ft or more.
     Here are the specs,
     Power supply:  6 MOT stack, center tapped ground (~12kV out 120V
in ?? amps, I don't have the tools to actually measure this) no
variac, full power or nothing.


On/Off is a little rough on the caps, but OK for now.


     Ballast: 1 MOT (shorted of course).


OK


     Tank capacitor:  75nf Maxwell, tested at 81nf (so the label says anyway).

     RF filter:  ohmite resister 50 ohm "chokes" filled with 4
welding rods for "inductance" and some ceramic capacitors about 600pf

Can cause HF ringing

(I don't know if it works or not, but there isn't much interferance
on our TV unlike my old (smaller) coil) and safty gaps to ground (I
don't use a mains ground at all, I use a seperate peg in the ground
from the RF ground for the MOTs and safety gaps).

     Secondary: 6in PVC 22AWG wound 31 in (+-1160 turns) three super
thick (uneven) coats of polyurethane.

     RF ground: copper pipe pounded in about 1.5 ft (the ground may
still be frozen down there).

Could be deeper. I use 6-ft. rod 5.75 feet down.


     Top load:  2 aluminum flex duct toroids covered in foil tape,
3in*15 and 7in*21 (I tried a large 11.75*42, but got no streamers
breakout with it connected).

     Primary:  1/4in copper (refridgerator) tubing, spaced .75in
apart with an 8in hole in the middle for the secondary.  Tapped
between turns 7 and 8, and sits just a hair below the first secondary
winding (no racing arcs yet, moving it downward  lowers the
performance, moving it up changes nothing).


OK


     Wiring: tank circuit-14AWG rated at 15kV, other wire-whatever I
had lying around (18AWG 20kV, some house wire, and some 22AWG magnet
wire, run through polyethylene tubing for insulation).


Probably OK if kept very short. Check for heating.


     Spark gap: (probably my performance killer) single blower static
gap, two brass bolts filed roughly to points (I use pointed contacts,
because smooth rounded contacts on my first smaller coil, instantly
gave me terrible (really, really bad) racing sparks, and the pointed
ones gave fairly smooth nice operation,) currently .75cm or just
between 1/4 and 1/2 in. seems to give best results.  My safety gaps
are set much narrower than this, but they have rounded contacts and never fire.


BINGO!!!   This is your killer. Pointed gap encourages corona 
formation and breaks down at much lower voltage. This is what makes 
it sound smoother. Ball type or cylindrical pipe gaps set 6 mm or 
less total will allow much higher charging potential before firing.

     I am building a synch rotary, but it will be some time until it
is ready, I do however have a much stronger blower on the way (the
currant one is lousey compared to the one that is coming).  The
output is Ok but somwhat inconsistant (I am running it outside, and
it is very moist here right now with snow melt and rain) sometimes it
will strike the strike rail 38in away while two additional long
streamers fly out in the air, and then a second later all you will
see is one tiny streamer 2.5 feet long or so, and it does everything
in between totally randomly.  Aside from building my rotary gap, is
there anything I can do to tweak just a little more output out of the
thing (a breakout point reduces the output, but makes it easier to
see as it doesn't move around the toroids).


Gap needs to be dry and clean. Towel dry everything and polish gap
faces with "crocus cloth"before each run. High humidity/dampness
in the air lowers the gap breakdown voltage.

Hope this helps,

Matt D.
Thank you much
Scott Bogard.








----------
AOL now offers free email to everyone. Find out more about what's 
free from AOL at <http://www.aol.com?ncid=AOLAOF00020000000339>AOL.com.