Hi Ron,Welcome to the TCML. Well, this is certainly a "hobby" and may end up "a lot more" if you really get into it. I don't use bottle caps except for other (non Tesla coil stuff). Your capacitance sounds reasonable. I wouldn't waste my time with bleeders on bottle caps as they are lossy to begin with. But, a discharge mechanism certainly would not hurt from a safety standpoint.
Regarding the arc voltage. You do want it as close as possible to the peak cap voltage. Javatc will let you know if the gap is too wide. This doesn't mean it won't arc, only that opening the gap exceeds the peak voltage of the cap. However, if the transformer has enough "umph", it can cause the cap to charge to a higher voltage which eventually arcs the wider gap. The higher voltage however risk cap and transformer death (usually the transformer, especially if it's an NST).
The arc voltage is based on a "smooth" and perfect spherical radius. Some gap electrodes don't quite meet this perfection. So, consider the gap spacing as a ball park value from a design standpoint. It's actually better if you connect the spark gap directly across the NST (like at a work bench) without anything else connected. Then adjust the spark gap distance as wide as possible where the NST output voltage arcs consistently. Leave your gap at this distance for your coil and you will have a "safe" and "properly" adjusted spark gap.
Also, for the secondary, consider 22 awg magnet wire. This will put about 1075 turns on the secondary for single build (which is fine for this coil) which is perfect. The existing primary is a bit wide for the secondary. So to get coupling up to par, the secondary bottom turn will need to be approximately 2.5" to 3" below the primary. This can be problematic at times. The only way to lower this differential is to add another turn on the inside of the primary. At that point, the secondary coil could be raised up. Right now, you have 4.36" between primary and secondary. A coil this size would ideally have about 1.5" distance.
Take care, Bart Ron Slack wrote:
Hello All, I'm an EE Student looking for a unique hobby, and coiling seems to fit me perfectly. I've been reading all I can find online for the last few weeks, including many of the posts to this list. I'm starting to come up with designs for my first coil using a 15/30 NST I got used from a local sign shop. Javatc says I need a LTR cap of 8nF for my tank. My plan is to use 5 wine bottle caps at a value of 1.55 - 1.62 nF each. Is there a good way to put a bleeder across caps like this? Also, I'm a little fuzzy on the design of my spark gap. playing with javatc for a bit, I came up with this: ---------------------------------------------------- Static Spark Gap Inputs: ---------------------------------------------------- 8 = Number of Electrodes 1 [inch] = Electrode Diameter 0.28 [inch] = Total Gap Spacing ---------------------------------------------------- Static Spark Gap Outputs: ---------------------------------------------------- 0.04 [inch] = Gap Spacing Between Each Electrode 21213 [peak volts] = Charging Voltage 20390 [peak volts] = Arc Voltage 34333 [volts] = Voltage Gradient at Electrode 72822 [volts/inch] = Arc Voltage per unit 96.1 [%] = Percent Cp Charged When Gap Fires 10.312 [ms] = Time To Arc Voltage 97 [BPS] = Breaks Per Second 1.66 [joules] = Effective Cap Energy 0 [peak volts] = Terminal Voltage 161 [power] = Energy Across Gap 31.9 [inch] = Static Gap Spark Length (using energy equation) is it a good idea to have my arc voltage this close to Vpeak or should I close the gap a bit more? I figure if I set my safty gap just a little higher than .28"/2 for each side to ground I should be good. for my primary I plan to use Primary Coil Inputs: ---------------------------------------------------- 7.5 = Radius 1 13.5 = Radius 2 0 = Height 1 0 = Height 2 12.5 = Turns 0.25 = Wire Diameter 0.008 = Primary Cap (uF) with a 6" by 30" secondary winding, altough I have yet to get some magnet wire. Thanks, Ron _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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