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Re: Ross-O's 1st Run - secondary arcing
Tesla List wrote:
>
> Original Poster: "Ross W. Overstreet" <ross-o-at-mindspring-dot-com>
>
> I made my 1st run of Friday night. I managed 31" arcs to a grounded rod
> before secondary arcing convinced me shut down. Here are the specs for
> my coil along with my Tesla URL. Please forgive the large pictures and
> slow loading of the page, I'm working on it...
>
> Primary: 15 turns of 1/4" copper tube with 3/8" spacing on a 45 degree
> angle
> Secondary: 6.275" SDR wound to 25.1" with #22 magnet wire
> Capacitors: .060" LDPE rolled cap, used .027uF for this run
> NST Bank: 12 kV -at- 106 ma
> Torroid: 7" aluminum dryer ducting, total OD is 29.5"
>
> See the page for pics and more details
> http://www.geocities-dot-com/CapeCanaveral/Cockpit/3377/
>
> I only managed to tune to the nearest turn before secondary arcing
> forced me to shut down. I had a heavy blue cone of corona from the top
> turn of the secondary down to the strike rail. It looked neat, but I'm
> afraid that the excessive ionization around the secondary may have
> facilitated the arcing problems. The 1st arcs originated from a
> "fisheye" in the varnish about 6" from the top of the secondary and shot
> straight down the coil to the ground connection. I put a couple layers
> of electrical tape on top of the bad spot and kept running. I noticed a
> few more of these coming from other locations. I raised the secondary
> about .75" and got a different sort of arc. This one came from the top
> turn of the secondary and only went down about 6". It formed a large
> brush shape almost as large as your hand. I quickly surrendered for the
> night.
>
> The good news is the 31" arcs while still somewhat out of tune. I was
> able to light a neon "R" at about 10' and could make a 4' fluorescent
> tube glow over 20' away! It's a beautiful thing - the sound, the light,
> the smell, all of it! Guess you could say that I'm thoroughly addicted.
>
> I had a hard time getting breakout without using a sharp point. I
> managed it twice before I shut down, and both times it came from the
> rough seam of the torroid. It seemed to prefer to break out on the
> secondary instead of the torroid!
>
> I fear that I may be overcoupled with the 45 angle on my primary. I can
> raise the secondary if I need to. Maybe I need to lower the torroid or
> make it smaller? I could get rid of several turns of primary and drop
> the ground rail several inches to help reduce the corona cone. I am
> really excited about running this thing again and could use some advice
> from you experts on how to solve this problem :-)
>
> I really want to thank all of the people who contribute to this list,
> especially the moderator (Hi, Terry) and the TCML webmaster (Hi, Chip).
> I have learned tons from this list and the archives. You all have also
> provided much needed inspiration during the sparkless months. The
> internet is a truly beautiful thing!
>
> Feel free to respond off list to <ross-o-at-mindspring-dot-com>
> Constructive criticism always welcome.
>
> Ross Overstreet
> Huntington Beach, CA
Ross,
Very nice looking system, Ross! I see you were able to get some help in
making your system - my spouse helped cut many of the LDPE and aluminum
foil sheets that went into the flat-plate caps in my system. The pride
of ownership helps... :^)
>From the looks of the system, with the secondary winding starting at the
base of the primary and a 45 degree primary, you're definately
overcoupled. This can be corrected by raising the secondary relative to
the primary (by several inches, most likely!). The "Christmas tree" of
corona between the top of the winging and the strikerail is a classic
symptom of excessive e-field or insufficient "shielding" by the toroid.
Raising the secondary to reduce coupling should help reduce this.
Once you've decreased the coupling, run the system in a dark room, again
looking for any signs of unwanted corona. If you're still seeing the
"Christmas tree", you may also want to lower the toroid relative to the
secondary. For best sheilding, the bottom-most part of the toroid should
be roughly level with the top of your secondary winding. This should
have the effect of increasing the e-field between the toroid and
strikerail, and reducing the electrostatic stress from the top of the
secondary to the strikerail. This tends to "throw" streamers outward,
and away from the secondary and strikerail. You've got a relatively
large toroid, which should be fairly effective at this. Adjusting for
best performance here is a bit of a balancing act. You may also need to
do a bit of retuning, since lowering the toroid will also lower your top
terminal capacitance a bit.
Finally, as you indicate on your website, you may also want to consider
migrating to a flat primary eventually, since an inverse conical primary
will not provide adequate clearance between the top of your coil and the
strikerail at higher power levels. This will ultimately limit the full
potential (NPI) of your system.
Safe coilin' to you!
-- Bert --