Jacob's Ladder

In Genesis, there is a story about Jacob having a dream about a ladder from earth to heaven.  This is also the name used to describe a high voltage traveling arc that rises over and over.  To get a decent spark through air you need around 10,000 volts to get started (it takes 30,000 volts to jump a centimeter).  However, once the spark is established it ionizes the air and makes it more conductive. 

Finally, some high voltage to play with!

Over the last few months I collected two old CRT TVs and a computer monitor.  These are easy to get for free because everyone is replacing them with flat screens.  They are on the curbs everywhere on junk pickup days.  What I wanted was the flyback transformer, you can see one on the near left corner of the table (it is all that is left of the CRT monitor I took apart).  I tried wrapping my own wire and hooking up a driver with a transistor (one can be seen next to the flyback transformer) but they tend to overheat.  I also tried hooking up the high voltage output directly from the TVs in the background using the built in board as a driver, they worked for a few minutes then burned out (I found out later it was because I had a bad ground connection; I hooked up another ground to use).  One was very dramatic and a capacitor started smoking and burned in two.  (I hooked up the highly insulated wire from the suction cups that were attached to the tube to one side and a ground to the other.)  It should go without saying that everything has to be discharged and grounded before messing with it.  I used a fiberglass « chicken » stick with a grounded wire connected to the end.

All I was trying to do was set up a Jacob's Ladder.  It is two vertical, uninsulated wires (in this case I cut them from coat-hangers) with a high voltage potential across them.  They spark across but the spark rises from heated air.  The wires are angled so that they slowly spread apart as the spark rises.  Eventually it breaks and a new one forms at the bottom.  They are commonly seen in old science fiction movie.  Here is a clip from the 1931 Frankenstein classic where there are several in the background.



Anyway, in the end a different approach worked best.  I hooked up the wires to a transformer from a neon sign.  M was indignant, she said I wasted some perfectly good TVs.  (I don't allow TV watching in our house despite the kids protests.)  While taking the monitor apart into a many little pieces, sometimes with a hammer, to salvage some parts T told V, "wow, dad really hates TVs doesn't he."  While the larger of the TVs worked it gave some very nice long sparks, but it buzzed very loudly before burning out.  This neon sign transformer can output up to 12,000 volts so it will do for now.

Here is a top view of the setup with a nice arc. 

By now the wires are very rusty (I've tinkered around to try to get this to work for several months now).  I suspect some of the yellow color is the rust burning off.  And by the way, don't read this and try to set one up if you don't know anything about electricity--this can be dangerous if you don't know what you are doing. Umm, also don't use anything flammable as a base, like the cork board I used; the arc can start a fire. 

Even though the kids complained about their « ruined » TV (I say it's an improvement) they still got a kick out of the sparks.