Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi James,With the primary, you'll have to see what will mechanically work for you. I would probably select the house wiring from the list given but may also consider the 1/4" tubing. From a current and voltage standpoint, the copper tubing is superior, however, with a small coil the size of yours, the mechanics are difficult and limited. The primary and topload greatly affect the external capacitance on the secondary as they are the nearest external objects. The larger the primary, the larger the primary's external C influence. Imagine the primary as a round flat plate (if a flat coil) or as a cylinder if a helical coil. Actually, from an external C influence, there is not much difference between a cylinder or a helical primary coil. The reason I note this is because the wire size on a tiny coil like this using 1/4" tubing as an example will only allow x-number of turns before the entire secondary is completely overtaken by the primary. If the helical is too tall, you'll only achieve hitting the primary with secondary strikes (unwanted). These are the common difficulties balancing electrical behavior and mechanical limitations (especially when one affects the other).
To raise your capacitance you must reduce your primary inductance because you want to keep the coil in resonance. It's the capacitive and inductance reactances which are inversely proportional. Now, if you keep the primary turns low (say about 5), then you can increase your capacitance proportionally. Because the turns are only 5 or so, the primary may still be low enough to not cause issues with primary strikes. It will however cover a considerable lower portion of the secondary. A side benefit is resonant frequency for the secondary lowering due to the external C influence on the primary is larger. This will also allow you to gain a little more C because you need a larger capacitance to lower the primary frequency in response to the secondary's frequency lowering.
This won't tell you what to do, but hopefully open up some avenues that maybe you haven't thought about. You may just want to experiment a little with different L and C values keeping in mind what is stated above.
Take care, Bart Tesla list wrote:
Original poster: "James Howells" <james@xxxxxxxxxxxxxxxxxxxxxxx>Thanks very much for your reply - I really appreciate it , and the others on the webI do have a 5Kv 100mA supply but wanted to start with something NOT attached to the main 240 Ac supplyIF I did want to pursue this secondary coil and ignition coil power supply which of the following materials I have would get it to workfor the primary.................... a) 0.127 dia. insulated house wire with solid core of 0.078 dia wire - b) 0.240 " dia copper tubec) copper strip ( some sort of ballast from an electric fork lift truck) rectangular section 0.1" x 0.3" wide.AND how should I wind it?I could build a RQ spark gap and a new capacitor bank - if you suggest that I need toYOU CAN SEE PICTURES OF THE SPARK GAP AND THE REST OF THE BUILD SO FAR AT http://photos.yahoo.com/jmshwlls www.SpamJab.com {UgzndUInruKjv2Cy9r} ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx> To: <tesla@xxxxxxxxxx> Sent: Wednesday, January 31, 2007 6:09 AM Subject: *** SPAM *** Re: Help required - ignition coil TeslaOriginal poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi James,The coil is really small and you have a lot of oddities (hv supply, primary, gap, etc..) and all that adds up to difficulty (for anyone).The primary is just like 18 awg magnet wire? Might work, but you will probably want to "not" make this closewound as you would a secondary. The small wire size has a much smaller radius of curvature and the breakdown voltage (turn to turn) would be greatly reduced. The small wire can also only handle a small current. When the gap conducts, heavy currents will try to make their way through that primary. Small wire will limit the amount of power (thermal losses).The cap also is super small. Your only 0.39nF (way down there). I know you likely sized it for resonance, but cap energy is another qualification to consider for spark lengths. I think your primary is close to resonance, there is just either too many losses or just now enough "umph" to do larger spark lengths.I suspect your basically seeing a brushy pink 1" corona looking spark off the end. If you "really" want sparks, find an NST about 12kV at 30mA. Install a fitting topload and build the primary and cap to suit the resonant frequency.I feel for you. Large coils are much easier to get working decently than those really small coils.Take care, Bart Tesla list wrote:Original poster: "James Howells" <james@xxxxxxxxxxxxxxxxxxxxxxx>I have spent every day since Jan1 working on my tesla and can not get more than a 1" spark no matter what I doTo save my sanity - some help is requested - I WANT TO GET BIGGER SPARKS!Power supply:- Twin Auto Ignition coils - 555 interrupter through two power transistors. A separate oscillator supply to main 12v battery-ball point pen case chokes - works wellSpark gap :- 6 mm copper tube fixed end to end but gap adjustable - best setting seems to be 0.1" Primary : 4 series 390 pF 15kv caps , and 3 in series 390pf 15kv caps ( should be 4 of each, but leg fell off one cap and no replacement yet) the three strings are in parallel{4 x 390} {4 x390} {3x 390}Primary coil wound on 4.3" plastic soil pipe ( sewer pipe) with .048" enamelled wire Turns 18 at present but was 30 and reduced it and tested one turn at a time down to 18 turnsSecondary: wound on 2.64" dia white ( abs?) plumbing waste pipe approx 450 turns of .019" enamelled wire to a height of 10.25 "Various toroid top loads have been tried ... and non , which works best!The present spark at the Tesla is about 1" which is about 20% of what I expectedI have not been able to improve on this - PLEASE HELP!I built a Tesla Coil Tester to match the resonant frequency of the coils ( it's a 555 and two LED job, and I think it works like the grid dip oscillator Thank one needed to have here for compliance with our Ham licence).The coils do show oscillation at the same point on this home made instrumentOriginally the tester had a range too high for my coils so, I had to double the oscillator capacitor inside the tester - and as a consequence lost even the crude calibration that was there to give me a quantative reading. This said, I think both coils resonate at about 800 kHz, and this is about the area my calculation show also.How close do I have to be with the frequency match ? Is it exact or nothing or is some mismatch possible but with reduced spark length?Thanks in anticipation of your replies James Howells <http://www.SpamJab.com>www.SpamJab.com {UgzndUInruKjv2Cy9r}