JACOB'S LADDER
Bill Beaty 1995

WARNING TO PARENTS: A "Jacob's Ladder" involves a transformer which produces between 5,000 and 30,000 volts AC. There is a serious electrocution hazard! Also, the electric arc produced is as hot as a flame, so there is a fire hazard. The projects described below should only be performed under strict supervision by an adult who accepts the safety risks.

"Jacob's ladders" are extremly easy to build. All you need is a neon-sign transformer and a couple of solid rods (coat hangers or heavy copper wires). Mount them on some kind of plastic insulating base, with the rods bent so one point near the bottom of the wires is very close (1/4" to 1/2"). The arc will strike at the closest part, then the heat will make it rise.

ADJUST THE ANGLE OF THE WIRES TO OBTAIN
THE LONGEST TRAVEL OF THE ARC

 \         /
  \       /
  \       /
   \     / 
   \     /
    \   /
_____| |_____<--- narrowest
  HH     HH <--__
                 -- insulating
                    supports

As with Tesla Coils, its easy to get a bad shock or even kill yourself. I treat the whole device with extreme fear, and always work on it by plugging it in while staying well away, watching, unplugging and making changes, etc. If you always make changes while holding the AC plug in your hand, it's hard to have an accident. If you add a fuseholder to your design, you can remove the fuse and reduce the temptation for kids to operate it without supervision.

While it's possible to build these devices with wooden supports, you run the risk of starting a fire should the spark decide to jump through the wood instead of through the air. Also, the arc/flame tends to make the metal hot, even though the current is pretty low in the vertical rods. Ceramic insulators and fireproof glass/metal construction materials are best.

Select a proper transformer. Output voltage must be several thousand volts, preferably more than 10,000v. The arc is low resistance, so when it appears, it shorts out the transformer. Neon sign transformers have a built-in series inductance, which limits the current when they are shorted so there is no problem in using them for Jacob's Ladders. Oil furnace ignition transformers are similar, although of much lower wattage. Other HV transformers will burn out or blow fuses when used to make arcs, since they have no short circuit protection. These types can still be used, simply put a 200W light bulb in series with the 120V line, so when the arc shorts the transformer, the voltage to the transformer drops and the bulb lights up.

The vertical rods need to be smooth, or else the arc will tend to get "stuck" in one place and jump upwards intermittently. Rusty, or plastic coated coathangers will make the arc act funny.

As with tesla coils, it's the wattage that gives the long arc. A 2000V transformer might only be able to START a spark over a tiny fraction of an inch gap, but once the spark has "lit", the bent wire electrodes can draw it out into a long flame. A 9,000v transformer might work better than a 30,000V transformer, if the 9,000V unit has a much higher wattage capability. Also, wattage is usually proportional to transformer size, so the more iron in the transformer, the longer an arc you'll be able to make. Power-pole transformers (if wired backwards to 120V and limited with a large AC heater in series!) can generate discharges several feet long.

One neat jacob's ladder: two long thin wires stretched between insulating plates mounted on floor and ceiling. The little flame starts at the bottom, where the wires are held close, and slowly rises along the wires all the way to the top. The arc really is a flame, so you need to use some sort of insulator panel at the top so the arc won't set the ceiling on fire!

NEON CHASELIGHT: one solid wire, with the second "wire" made of many small segments with curved ends, then many small neon bulbs connected to bridge the gaps between segments. As the flame rises, the neon bulbs turn on in sequence. Can't run this one for too long, since the little neon bulbs are overdriven and get extremely hot!

DNA LIGHTNING: spiral the solid wires like DNA, so the flame rotates as it rises. This is a bit hard to do if you spiral them too tight, since the arc will try to jump to the wire above or below, instead of across.

ELECTRIC BRANCH: support some wires bent in a V-shape, between the main rods of the device. As the flame/arc rises, it gets divided into TWO separate rising arcs. I managed to do this repeatedly and make six separate arcs, but they weren't too stable, since if one goes out, all will stop.

      \  \     /   /
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         \  |  /
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      _____| |_____ <--- narrowest
        HH     HH  <--__
                        -- insulating 
                            supports

PLASMA SNAKE: I built a J.L. inside a 6" glass pipe 2' tall, with glass plates closing the ends, then filled the pipe with argon from a welding supply. This converts the arc from a short flame into a very long writhing white snake. I could bend the wires to triple the arc length on the same transformer. I had to keep a slow flow of argon going into the pipe, since the tiniest bit of air acts to "poison" the effect. Helium is supposed to give pink discharge, and neon a red discharge, but I haven't tried these gases.