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Re: A few problems..



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Matt,

Thanks for sharing the basic specs at the bottom of your post. Don't be depressed if you don't reach the 28" spark length. Feel real good if you get close 20" to 22"! Your coil is large enough to run a 12/60 NST if you feel up to it. The specs indicate your coupling is too high (which explains your periodic racing sparks). Adjust your secondary so the bottom turn is 1.5" below the center line of the primary's top turn (due to your particular . This should result in a coupling of 0.12. I would probably do that before winding a new primary.

Your max sparklength expected is 24" with your particular NST (not 28"). Yes, only 4", but calc's I use don't show 28", even on a good day. Once you adjust the secondary, you will likely only notice that racing sparks are not occurring and no change to spark length. This is normal. Now, work on you spark gap. Rebuild it if necessary. This is the obvious component for losses and is where the best increase in sparklength is to be realized. Much "power" is lost in the gap. Minimize the power lost at the gap and you will increase the power available for output sparks. This is not always easy, but it is definitely a very important arena to do battle in (up to 50% losses in the gap on average). Any increase there in efficiency goes a long way with spark lengths. Anyone who has coiled long enough realizes the importance of a "good" spark gap. It can make or break a coil.

Take care,
Bart


Tesla list wrote:

Original poster: "M G" <gt4awd@xxxxxxxxx>

Hi everyone,

I finished my first coil a little more than a week ago. A 4" spark gap coil, using a 9kv 30ma NST, and eleven 2kv .15mfd CD capacitors in series. For past week or so I have been adjusting certain parts of the coil to get better output. My recent changes include making a tap for capacitor eleven, which helped increase secondary streamer output by some. Raising the secondary coil up more to prevent overcoupling racing arc's. Still seems to happen on full power runs.

The secondary appears have not received any damage from the problems, but I will probably add more polyurethane coats just in case. Some may remember that my primary is at too high an angle, 55 degree's. Is it time to just scrap the primary and make a flat spiral or can I get good coupling just by raising the secondary up more? So far the best output of the coil is only around 12-14", which is no where near the 28" that should be possible using a 9kv 30ma PSU. The coil uses a "Terry filter" setup as shown in the standard filter schematics. I was wondering if the filter degrades overall performance some in trade for less stress on the NST?

The toroidal topload, 4"x8.5", is made from aluminum ducting, and covered in aluminum tape in an attempt to smooth out the sharp points some. Secondary end is connected to topload by end of the wire. I have yet to make the secondary top end cap. Secondary bottom ground, with end cap, is made with end wire wrapped around solid brass bolt. I would appriciate ANY suggestions for improving the coil output. Max output is around 10" with occasional 12-14" air stramers.

All of the images I have taken so far of the coil can be viewed on my imageshack public page.
Link: http://profile.imageshack.us/user/gt4awd/
I would just put links if there was not so many images.

Here are some coil specs I did not mention.

Secondary: 4.20"x20.25" using 26AWG single build magnet wire on thin wall pvc.

Primary: 55 degree angle using 10AWG non-insulated solid copper wire. Tapped at turn 9.7 with a total of 11 turns. Inside diameter is nearly 7", outside diameter 13", height of 4.5", and primary turn spacing of about 1/2". Both connections leading to primary are nearly 2' long.

Wire: Primary circuit wire and ground wire using 12AWG insulated solid copper wire.

Filtering: Standard "Terry Filter" for high voltage end, and a 2x10 amp CD RFI filter for mains line.

Ground length: Coil support stands about 2' above ground level. Ground wire has a total length of around 15'.

I might be missing some important information. Let me know if I am.

Thanks,
Matt G.

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