Hi Ben,The small coil causes a few strait forward problems. First, it's obvious the frequency is high. By itself, about 1.4 Mhz. This affects penetration depth to 2.73 mils (under 3 thousands of an inch of the wire is conducting the majority of the current). This results in AC losses near 80 ohms.
Second, the small diameter results in a very small inductance about 2.2mH. The inductance stores energy charging your top terminal to some capacity. The top terminal is small and can only store a feeble charge and the secondary is just not capable of charging a large top load. So a small coil is limited and also has higher AC losses due to the frequency. In the end, you get about a 2" or 3" spark (or maybe slightly more if you figure out how to optimize the coil).
A larger secondary can store more energy and thus transfer a greater charge to a larger top load storing more energy available at the point of breakout. What DC said is true. I hope this helps explain why. The most I've got out of a 2" coil is about 4". It started at 2" in which I increased toroid size to about 2" x 8". Just like any other coil, the larger the top load, the longer the sparks, but there is of course a limit of both time to charge and charge voltage (this is true for any coil).
Due to difficulty at guessing at toroid sizes, we often use dimensions we "think" is good and do the best we can with it. Top terminal sizing can be difficult to find the "best" size for the situation. There are numerous dimensions and we can't build them all. Think of it: the same tube size, but increase the horizontal dimensions. Or, keep the horizontal dimension and change the tube size. Or, do both. After all of that, change the height of the top terminal above the secondary. In otherwords, the number of possibilities and it's relationship with the application are endless. Toroids are difficult to make and expensive to buy. And so I say again, we do the best we can with determining a good toroid size for our coil and hopefully it will perform well. This is one area where experience helps, but experience is not vast simply due to the number of possibilities. However, there are some obvious limitations that help put a window around the possibilities.
Take care, Bart Ben Sneath wrote:
The 1.75 inch dia sec is going to severely limit your output spark. My estimate is 3-4 inches max. Going to a larger dia sec will improve output. Resonance Research Corp. www.resonanceresearch.comExactly how does this small diameter prevent long sparks? does it not have enough inductance? would you please explain how diameter limits spark length... it is wound with 434 turns of 30 gauge wire from a degaussing coil from a computer moniter, winding length = 6" toped with a 1.5x4.7" toroid Ben _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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