Re: First light...Mixed Emotions

["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 11/18/02 6:23:51 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:


>Hi everyone,
>
>Well, tonight we fired up our second coil after many sleepless nights
>building it. It worked, but this coil right now is really bad-tempered. We
>got sparks almost EVERYWHERE. It comes off the wire that goes to the
>primary and hits the secondary, sparks along connections between wires,
>saftey gaps, primary to secondary, the secondary along itself, and oh yeah
>- a little off the toroid =P. We were able to clean it up a littlle and got
>rid of most of the unwanted sparks, but we are still getting hits from the
>primary to the secondary and along the secondary itself. Sigh - We are now
>putting a few more coats of polyurathane along the secondary which should
>insulate it better and will hopefully get it running again by tomorrow
>night. I'll try and get some pictures posted soon. (once it works)
>
>Dimensions are here if anyone cares.
>
>Power supply: 9kv 120ma NST. This is a BIG NST. Only RF protection is
>saftey gaps.
>
>Spark Gap: RQ spark gap w/ vaccum motor to pull air through it.
>
>Capacitor: LTR that has 2 strings of 6 geek caps with a total of .05mfd
>
>Primary: 13 turns of 1/4 inch refridgerator tubing spaced 1/4 inch apart
>and tapped at about turn 8. The inner turn of the primary may be too close
>to the secondary (1.5 inches) but we don't want to be cutting off inner
>turns yet untill we're sure.
>
>Secondary: 6.25 inch outer diameter PVC wound for 24.5 inches with 22 gauge
>magnet wire. We are triple coating the coil again to try and get rid of
>those sparks.
>
>Toroid: 28 inch outer diameter with 4 inch flex duct. This probably needs
>to be covered in aluminium tape and smoothed out as we are getting lots of
>very tiny (10 inch) sparks all around the perimeter of the coil but no
>actual streamers.
>
>Sorry if this post is a little long. I hope we can get this one to work
>better than the last one. (12 inches at most, it was really sad)
>
>
>-Chris


Chris,

Some comments.  Free advice:)
Your coil is similar in size to mine.    Are you sure this coil is in 
tune?  I ran some calculations and found that it should tune at or near 
turn 7 on the primary.  I have found best results by selecting a primary 
cap that allows the use of the largest number of primary turns.  A larger 
primary will produce lower gap losses and be easier on the primary 
cap.  Are you using a variac to bring up the primary voltage slowly?  I 
would not do it any other way.  After making some major adjustments to my 
coil (like new primary cap or toroid), or with a new coil, I calculate the 
required number of primary turns that should result in the primary and 
secondary systems running at the same frequency and start there.  I place a 
breakout wire on the toroid with a ground wire maybe 6" away to start.  I 
turn on the gap blower, wait for it to come up to speed then slowly crank 
up the variac.  As the spark gap starts to fire, after yo! u gain some 
experience, you will know how close you are to being correctly tuned.  If 
it sounds weak and tinny the primary tap is probably at least one turn 
off.  Move it one turn up or down and try again.  You want a hot, lower 
frequency, sound from the main spark gap.  Once you get here, slowly 
increase the variac.  Pay particular attention to the secondary.  You want 
no sparks coming from the top few windings of the secondary and of course 
no sparks breaking out in the middle of the coil.  If you have either of 
these, first lower the toroid to provide more protection for the top of the 
coil.  If this fixes the breakout on the top windings but you still have 
breakout in the middle of the coil, you are either still not well tuned or 
you have too much coupling from the primary to the secondary.  Try raising 
the secondary up in .50" increments until this stops.  Now slowly increase 
the variac up to full power, again watching t! he secondary for 
problems.  After destroying one secondary! , I pay real close attention 
until I get everything adjusted just right.  There are a lot of variables 
that need attended to.  I do the final tuning adjustments by slowly 
increasing the gap distance on the breakout wire and just tuning for 
maximum spark.  Finally, remove the breakout wire and slowly crank up the 
variac again.  If no sparks breakout from the toroid, the toroid it is too 
large for the amount of input power.  For that situation, you either need 
to leave a breakout wire (or bump) on the toroid, go to a smaller toroid or 
apply more power - add another transformer in parallel, etc.

Good luck, Ed Sonderman