[TCML] LTR/STR and spark length

[bartb]

Hi Neal,

Something else I wanted to say about the gap your using now. I believe 
these are the drawer pulls with a slight radius to it's facing surface 
and yes, it's mostly flat. This gap will require you to keep a somewhat 
narrow gap, but in doing so, it does allow a small bang size and 
probably small enough to keep the gap running. My brass gap was brass 
rod stock 1/2" diameter. It was built in an RQ style. The gap width was 
quite a bit larger. Due to that, it did take a decent voltage to arc the 
gap. What I found was that the sparks started out nice and long, but 
after a few seconds, the sparks started diminishing greatly. This 
occurred due to the heat buildup over the few seconds of running. I 
couldn't keep this gap cool even with a great deal of air flow. Now, if 
the gap had been very narrow, then the arc voltage would have been very 
low resulting in a small bang energy across the gap, and probably would 
have run similar to your gap. Tubing was much easier to keep cool and 
resulted in much better performance.

With your gap, I would recommend not going any larger than 0.2" total 
gap width. This is based on a relatively cool gap. In reality, as the 
gap temp drops due to heat, the numbers for gap spacing get wider and 
coilers thus do get away with a larger gap space. But, this is all 
dependent on gap temperature, geometry, and their associated arc voltage 
and bang energy. Those at least are what I personally consider important 
in a static gap.

The physics are simple. It's easy to realize how electrode geometry and 
distance affects the arc voltage, how temperature affects the arc 
voltage, what type of electrode makes a good heat sink to "stabilize" 
the arc voltage to something near the desired cap charge, how air 
greatly aids this process, how keeping the arc voltage stable and at the 
desired value correlates to bang energy, and how bang energy affects 
spark length. It's then not hard to design a gap that works well with 
the system. In the same respect, it's easy to see why some gaps are not 
a good design for a particular system, and with your power, the gap 
appears to be the main area for improvement. In every coil I've built, 
the gap improvements I made had the greatest impact on performance 
beyond anything else done for the same power used.

Take care,
Bart


> Neal Namowicz wrote:
>> Hi, and thank you to everyone for your responses-
>>
>> Bart, it's very interesting that our coils are so very similar.....   
>> except for that whole, underperforming thing on my part. Let me give 
>> you a little more info on my specs before we go on.
>> My first topload was a dryer-duct, covered with foil tape, type, 19 
>> 3/4" X 3"
>> I had arcs off of it, but from all over the place, even with a 
>> screw/breakout point taped to it.
>> So for the moment, at least for consistency purposes, I'm sticking 
>> with a 10" ss sphere with a 12 5/16" steel rod inserted into it. All 
>> the arcs are headed relatively straight up now.
>> My gap is single static, quenched with a blower/motor from a 
>> microwave. The electrodes are round, "almost flat" surfaces, 1" 
>> across, made out of brass (old drawer pulls). I'd like to stick with 
>> a ssg for now, but, if I feel ambitious, I do have a couple little 
>> motors around that could probably give me at least an asrg.
>> Since my last email I tweaked a couple things, and I'm getting easy 
>> 24+" arcs now. I opened up the gap a little bit, but still backed off 
>> if I got any arc on the safety gap. I also ground a mild point on the 
>> rod sticking out of the sphere. Racing arcs were mentioned earlier, 
>> but the only time I experienced them was very briefly while adjusting 
>> the primary tap.
>> *Could you explain how one goes about determining the resonance for a 
>> given system, so that they could know (within the proverbial 
>> ballpark's range) as to whether they are str/ltr/R? Thanks everyone,
>>
>> Neal.
>