Jacob’s Ladder

 

 

Of the many Hi-Voltage projects, I never quite seem to tire of watching a Jacob’s Ladder device in operation.  This simple device is nothing more than an elongated vertical spark gap connected to an HV source, yet can be fascinating in its beauty, sound, and behavior.  If constructed properly, the Ladder may be allowed to run for quite some time without negative effect (CAUTION: never leave such a device energized and unattended or operate it unshielded around children or animals). It is arguably the simplest to construct of common HV projects and highly recommended as a starting point for beginners by most experts. Since many of us are also new to this interesting avocation, this is where we have begun our experimentation. 

 

The Hi-Voltage source may be as diverse as a car ignition coil, a neon sign power supply (NST), a utility distribution transformer (pole pig), or other even greater potential sources with striking differences between the sound and visual effects of each.

 

 

 

COIL	NST	POLEPIG

 

 Any source other than the first two will require current limiting ballast to prevent damage to the power source or the household electrical system.  The gap electrodes may be constructed from almost any rigid conductive heat resistant material.  Popular favorites include heavy gauge bare copper wire (e.g. #4) and copper tubing, though I have even seen a coat hangar used on a very small unit.  The two upright electrodes are constructed and secured at the bottom in a ‘V’ shaped formation, with the lower ends relatively close together (~1/4” for NST powered ladders is usually a good approximation) and the upper ends diverging from each other to a greater or lesser degree depending on how great a potential difference will exist between them.  The HV potential is connected at the bottom near the point of closest proximity for the most consistent results.

 

It usually takes a little ‘tweaking’ of the UNENERGIZED device to set the spacing exactly right.  When energized, a Hi-Voltage plasma arc forms initially at the point of closest proximity.  Then, because of the high temperature of the plasma, convection currents set up in the surrounding air cause the arc to rise up the spreading ‘V’ of the upright electrodes until the arc is drawn out to its maximum sustainable length, at which time the arc is extinguished and another forms at the base to repeat the process endlessly.  If this sounds like something you remember seeing in some ancient Sci-Fi flick, you would be correct in your association.   JL devices were used quite extensively during the early days of filmmaking as props to convey the feeling that science, especially of the dark, wild, and unrestrained type, was being done.

 

In my own recent experiments, I have been studying the use of aluminum bar and tube.  1-inch square aluminum tube has proven to be my favorite for several reasons.  The way the rising plasma weaves and crawls across the surface, slowing its ascent and this coupled with the sort of crackling sound this produces gives an especially pleasing effect.  Also, the extreme rigidity of the material in contrast to copper tube or wire allows the practical use very tall designs.  My current incarnation may be used with either a Very High Voltage source (I have been successful with 0.1 to 0.2 Megavolt) outside or with a low power HV source indoors (I use both: 16,600 Volts at 60 ma. and 14,300 Volts @ 120 ma. from  ~ 10% overdriven NST sources) and it is just short of 8 feet tall. 

 

The sound and the way the surface reflects the colorful glow of the plasma makes it a striking attention getter in the entryway.  My simple base design allows movement in 2 planes to either increase the gap at the bottom or rotate the uprights to open or close the ‘V’ and eliminates the need for direct connection to the power source or bending/bowing of the conductors.

 

Of the 4 that I have set up about the house, the smallest is less than 18 inches tall and powered by an automoblie ignition coil.  It is constructed based upon a design scheme I found at the remarkable website of Greg Hunter (Greg's Garage) using only a standard light dimmer and a 24 uF 370 Volt motor run capacitor to control the coil.  Gap uprights are out of #6 bare copper attached to a PVC base.  50 kV television flyback wire is used to conduct the HV from the coil (do not use automotive coil or sparkplug wire – most types are resistive in nature).  The transitions are rapid and the sound is startling, reminiscent of an angry swarm of hornets (on steroids with a loudspeaker!).

 

Medium sized units were constructed with gap electrodes of #4 AWG bare copper wire (up to 2.5 feet or so) or ½” copper tube (up to about 5 feet tall) and powered by pairs of NST’s with both of their inputs and outputs wired in parallel.  To perform this type of connection, it is best to use a pair of identical NST’s.  The inputs are wired: Line to Line, Neutral to Neutral, and Ground to Ground and the outer metal cases are connected together.  The output terminals are then connected in pairs and IN PHASE with each other (to give zero voltage between them).  To determine the proper connection, the parallel wired inputs are energized with an HV rated wire attached to one output terminal of one transformer.  With a properly insulated or non-conductive rod, the free end of the wire is brought near one of the output terminals of the other transformer.  If little or no electrical activity is seen, the system should be de-energized and those 2 terminals connected to each other (the same for the other pair of terminals).  If, on the other hand, a high voltage arc is produced, those 2 terminals are not in phase and SHOULD NOT be connected to each other, but rather, each should be connected to the OPPOSITE side of its respective partner transformer.

 

I have also found that a specially constructed adjustable, cooled, and filtered power supply between the NST’s and the mains is helpful with large Ladders:

And speaking of LARGE ladders, here is a not-so-good PowerPoint show of our 200,000 Volt Ladder running at about 175 kV and 0.15 Amp. CLICK HERE (Power supply is a little large than the one pictured above - it weighs about 1000 lbs!)