# [TCML] JAVATC - Question

Sun Mar 15 09:00:47 MST 2009

```Thanks Bart.? I think I got it now.? I try playing with the variations as you suggest to get a feel for the differet size-geometry relationships.

One other question, you mentioned the drawer knobs tend to heat up and are tough to cool.? I will be using air blast for cooling & quenching.? I removed the motor/fan from a vac from an old vacuum cleaner which seems to put out a pretty intense airflow out of a 1" X 2" opening.? Do you think this would?be sufficient to?handle the cooling need?? I hear of a lot of guys using brass bar stock in these gaps which I would think have similar heat issues.?

Dennis

-----Original Message-----
From: bartb <bartb at classictesla.com>
To: Tesla Coil Mailing List <tesla at pupman.com>
Sent: Sat, 14 Mar 2009 5:35 pm
Subject: Re: [TCML] JAVATC - Question

Hi Dennis,?
?
I think I know the knob style your referring to. It's radius of curvature at the face is much larger than that at the edges. Well, I would select "round" for the input and use the face curvature (not the edge). When the curvature is much larger than the gap distance, it will function very near to a flat surface anyway.?
?
You can test this in Javatc. Just set for 2 electrodes, 5" diameter, 0.1" gap spacing. Use say a 12/60 or whatever in the transformer area (and a cap up in the primary section). Then calculate the static gap section with "round" selected. Look at the arc voltage and note it's value. Then select "flat" and recalculate. You'll find the arc voltage changes very little. Then change the electrode diameter to 1". Redo both round and flat selections. You'll find the arc voltage is still very similar, but a greater degree of variation. Finally, begin increasing the gap distance and redo both round and flat selections. You will now find an even greater degree of variation between the two equations.?
?
As I mentioned, I would use the "round" selection for the geometry and attempt to use the face curvature for diameter. As the gap is increased, the curvature begins to affect the arc voltage. But if the curvature is very large (say your face curvature diameter is 5"), then the gap will still appear very flat even with moderate gap distances. The only time I would use the "flat" selection is if say I had solid stock that was cut flat on the ends, otherwise, I'll always use the round selection and call out the curvature diameter (as if the curvature were a sphere and whatever diameter that would be).?
?
Good luck with the drawer knobs. They do come in handy for safety gaps, but for the main gap, they can heat up quickly and are difficult to cool.?
?
Take care,?
Bart?
?
> Bart or anyone, I have a question on the Static Gap Design input.? I am considering a single gap design using 2 knobs from cabinet doors or drawers.? The diameter accross the face of the knobs is 1.25".?
>?
> First, should I input "round" or?"flat" for Electrode Geometry?? I always assumed round was used for copper pipe electrodes only, but now I'm not sure.? The face?of the knobs where the spark would?occure is rounded/convex - seems like I should input 'round.'? >?
> Second, how should I determine the Electrode Diameter I need to input?? Is is the diameter measured?across the face of the knob?? Or is it some calculation of diameter based on the radius of curvature of the rounded face of the knob?? The former would be 1.25", but the latter would be considerably larger.?
>?
> Thanks for your help - Dennis Hopkinton MA?
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