Re: larger than resonant (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 04 Jun 2007 17:49:43 -0400
From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: larger than resonant (fwd)

Bart,
     The glass jars are very thick, .2 sound about right (I assumed they 
were thinner for the rest of the jar, but they are about .25 in thick at the 
neck).  Thanks for doing all the calculations for me, perhaps I'll rewind a 
new secondary when I get some time, I have a bigger better coil already, but 
it would be nice to have my small one working better (the OBITs have been a 
very reliable power supply for me, unlike my MOT powered six inch coil, 
which has been somewhat stubborn).  As for the capacitors, if I don't feel 
like buying some, I have a gazillion feet of green house plastic 
(polyethylene) that would be at least a step up from the jars, and it 
wouldn't be too hard to make one for 12.5 nf and about 20 kV (assuming 
correct dielectric constant and breakdown voltage).  Thanks again.
Scott Bogard,


>From: "Tesla list" <tesla@xxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: larger than resonant (fwd)
>Date: Sun, 3 Jun 2007 17:11:30 -0600 (MDT)
>
>Original poster: List moderator <mod1@xxxxxxxxxx>
>
>
>
>---------- Forwarded message ----------
>Date: Sun, 03 Jun 2007 11:38:05 -0700
>From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: larger than resonant (fwd)
>
>Hi Scott,
>
>As you already know, the coil needs more turns (only 340). But, I looked
>at the coil "as is". I modeled the coil at your tune point of 6 turns
>and inserted a strike ring as a grounded object and 3 other rings to
>represent the 3 unused outer turns (they have a slight effect as an extC
>to the overall frequency). Here is the graphic representation from Javatc.
>http://www.classictesla.com/temp/sb340.gif
>
>The reason I took the time to throw the grounded objects in there was to
>back calc the bottle caps. The system frequency is about 710 kHz. For a
>6 turn tap position, the tank cap needs to be 6.28nF, so if your using 3
>caps wired in parallel, then each jar is about 2.1nF, which is not what
>I expected. This indicates a wall thickness abut 0.2" (assuming
>dielectric constant of 7). I expected something nearer to 3.2nF per jar.
>But, it is what it is. "If" your 6 turn tap position is near resonance,
>then 3 caps in parallel are 6.28nF.
>
>BTW, the difference in the 3 extra turns from an extC component is 2.5
>kHz and the strike ring is 10 kHz. So not much affect at all (like I
>said, I just wanted to back calc the tank cap as close as possible).
>
>I tuned the coil for 2 caps (4.2nF) and the primary would tap at about
>7.25 turns. For 1 cap (2.1nF) at 10 turns. So, you could get 2 or 3 jars
>to work, but not 1. I think your running STR anyway, so the 3 jars would
>probably do better. You don't gain much between 6 turns and 7.25 turns.
>
>Well, how to make it better? Wind a new secondary: Example 3.5" x 17.5"
>using #28 for 1200 turns. You would want to rebuild the primary also 4"
>x 16" using 0.25" tubing. This coil would require a 0.0125uF tank cap.
>So, you could probably get away with a single string of 12 caps using
>0.15uF CD type (considering the OBIT's are only 10kVrms). About $40 or
>so for the caps.
>
>See, a whole new coil (but you get to keep the topload).
>
>For the coil at hand, the I see that might be of benefit is to replace
>the needle gap for a nice airblown pipe gap of some type. With the power
>your running, you really should be seeing between 40" and 50" sparks. I
>built a large coil once which was short in the h/d category (about 700
>turns). What really helped that coil out was to add length. Because it
>was sonotube, I literally added 12" to the length (took some work to
>do). This helped in more ways than just h/d and secondary inductance, it
>also allowed me to use more primary turns for the same capacitance which
>helped increase surge impedance and allowed finer tuning. A new rsg also
>helped a great deal.
>
>Take care,
>Bart
>
>Tesla list wrote:
>
> >Original poster: List moderator <mod1@xxxxxxxxxx>
> >
> >---------- Forwarded message ----------
> >Date: Sun, 03 Jun 2007 01:10:54 -0400
> >From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
> >To: tesla@xxxxxxxxxx
> >Subject: Re: larger than resonant (fwd)
> >
> >Ok,
> >Toroid, Od 14.5 inches, chord, 3.5 inches, height from floor 46.75 in.
> >Secondary 20 AWG, 3.5 in PVC form, wound 12 inches, height from floor 
>28.75
> >inches.
> >Primary, .25 in cu tubing, 4 in ID 16 in OD (turns aren't spaced very
> >evenly, the average space is .3 in, the last turn is spaced wide but not
> >used anyway, it tunes best at 6 turns, and has a total of 9) height from
> >floor 28 inches.
> >Capacitors, jar dimensions, 3 in radius filled 12 inches, glass thickness
> >unsure but believed to be .125 in.  I think they probably put out about 
>3.5
> >nf put together.  (one gallon pickle jars)
> >spark gap, single air blown gap "static" (to bolts filed to points) I 
>once
> >tried a asynch, and got good results the faster I turned it, but the SG 
>blew
> >up before I cranked it very fast.
> >RF ground, metal floor support (not good enough! but very convenient).
> >Power supply, 4 OBITs in parallel, 10 kV at 92 mA current limited total.
> >All wiring is 14 AWG high voltage wire.
> >
> >I don't have any tools to measure capacitance, but I could probably 
>borrow
> >one and find out for sure.  Let me know if you need additional specs.  I 
>get
> >about 12 inch arcs to a grounded object, and the free fliers are about 
>20ish
> >inches.  It was my first coil, so naturally it was made rather sloppily,
> >hence the unevenness of the primary.
> >Scott Bogard.
> >
> >
>
>
>

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