[TCML] Climbing Arcs

[Bert Hickman]

Hi Tony,

Some suggestions:

1. Use a wide "V" to more rapidly spread the arc. The higher the current 
the wider the end gap should be
2. Use inductive ballasting for best performance
3. Use smooth rails to avoid incandescent "hot spots" that will cause 
the arc roots to temporarily hang in one spot. I'd recommend using 3/4" 
hard copper pipe or non-magnetic stainless steel tubing. Periodically 
remove any oxide buildup. I suspect the oxidation of the galvanizing may 
a major part of the problem you're seeing.
4. Enclose on 4 sides to reduce disruption by air currents. Leave top 
AND bottom portion open to permit vertical air flow. Be sure to leave 
plenty of clearance on either side of the gap, especially for a higher 
current ladder.
5. For grins, try connecting a small (500 - 1000 pF) HV doorknob cap 
across the gap to make for "snappier" performance at start and at long 
arc lengths.

Good luck,

Bert

Sfxneon at aol.com wrote:
> Hi Ken,
>  
> You're right, the arc climbs because it's hotter and less dense than the  
> surrounding air. I've had no problem making the small NST powered ones work, but  
> at higher currents the middle of the arc tends to rise faster than the ends. 
> It  grows in length but hardly ever makes it to the top of the rails, even 
> when set  close. It seems to get stuck along the way and doesn't want to climb 
> smoothly. 
>  
> Does anyone know if the smoothness of the rail's surface or the zinc  coating 
> would have anything to do with it? 
>  
> Thanks, 
>  
> Tony G
> 
> In a message dated 5/27/2008 8:47:52 A.M. Central Daylight  Time, 
> kwillison2 at cox.net writes:
> 
> I never built a really large one. I have however observed that any  air
> movement across the ladder will disrupt the arc. Conducted some  experiments
> tilting the electrodes from vertical it would not work beyond 30  degrees.
> The curve of the arc remained vertical while the electrodes were  tilted. I
> surmised that heat causes the arc to rise and heat raises  vertically so
> won't work when it passes about 30  degrees.
> Ken
> 
> -----Original Message-----
> From:  tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On Behalf
> Of  Sfxneon at aol.com
> Sent: Tuesday, May 27, 2008 12:10 AM
> To:  tesla at pupman.com
> Subject: [TCML] Climbing Arcs
> 
> Hi All,
> 
> I have a  spare 12.5 kVA/20 kV bombarding transformer and sliding choke   with
> 
> which I'm building a large Jacob's ladder using 3/4" x 10' EMT  conduit. It  
> works reasonably well, but the arc tends to rise up the  rails too slowly and
> the 
> middle of the arc outruns the ends, resulting in  a restart before it
> reaches 
> the  top. I've adjusted the angle of the  rails from near parallel to about 
> 18" apart  at the top, without much  success.
> 
> Does anyone know how to tweak the performance of a big climbing  arc so that
> 
> it will climb to the top of the rails more often? I'm  guessing that
> increasing 
> the air convection around the arc would help it  to climb, so will
> inclosing 
> it in a tall clear tube or box make a  difference? Does the material  that
> the 
> rails are made of have any  effect? How about the ballasting  of the 
> transformer, as far as  inductive or resistive, etc? 
> 
> Thanks,
> 
> Tony Greer
>  
> 
> 
> 
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