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Registered Member #611
Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79
I'm making good progress on my coil. I have finished the main spark gap as well as a "terry filter" and the toroid. I picked up some oak to make the stand, and a sheet of polycarbonate to make the primary standoffs.
The issue I've ran into is how to space the primary and secondary. Is there a good ballpark figure? How close is too close? I've spent hours plugging in different dimensions into javatc and noticing how it effects the K value. I've come to the conclusion that these numbers will mean little to me until I can get my hands dirty, so to speak.
I have so many questions on this subject that it is making it hard to write this post. I guess I need to know how close could arc over and how far would energy transfer become inefficient / ineffective? My mental vision of how this works is showing me about 1 to 2 inches is where I want to be.
The dimensions of the secondary are 30" of 6" diameter wound with 22 gage. I have a 50' coil of 1/4" od copper tube to make the primary. I've left very little room in the planned design for vertical adjustment of the secondary, 1/2" maybe. I can go back to the drawing board on this aspect if need be.
Please respond to this post, and please try not to eat my noob ass alive. I am very humbled and embarrassed that I have to post such questions in the first place.
Registered Member #611
Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79
Sulaiman, how were those figures determined?
To achieve 0.18, the design calc keeps putting the bottom turn of secondary several inches below the first turn of the primary. This doesn't seem normal from what I have seen in other peoples coils.
The starting point dimensions I'm using for the primary are 15 turns of .25" with .25" spacing between turns and the first turn spaced 1.5" from the secondary. The bottom turn of the secondary is level with the primary. From there I plugged in .18 as the desired coupling and the results were that the bottom turn of the secondary is placed more than 2" below the primary.
I've tried tweeking the spacing between turns of the primary and the spacing between pri and sec, both with and without topload, all with similar results. Where am I going wrong?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I didn't work out the figures, they're (I believe) generally reccomended. The coupling coefficient affects many things, one of the most important being the number of cycles to the first 'notch' (the point at which all energy stored in the primary is transfered to the secondary) some figures that I have (forgotten source) are
#cycles k 1.0 0.600 1.5 0.385 2.0 0.280 2.5 0.220 3.0 0.180 3.5 0.153 4.0 0.133 4.5 0.117 5.0 0.105 5.5 0.095 . . The general idea is that the more cycles that energy remains in the primary, the more energy is lost (in the spark gap) If you try for a very tight coupling you will probably get pri-sec flashover or 'racing-sparks' on the secondary also tighter coupling splits the pri-sec resonances farther apart in frequency. So it's a compromise.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
you shouldn't get stuck on figures and numbers, especially if you are a beginner coiler. Best to simply build your coil, and experimentally determine the operation of your coil by raising and lowering your secondary.
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Stuck on coupling issue
