wolit (04/17/83)
As a follow-up: which is the best choice, AC or DC? I would guess DC because it would not try to extinguish itself by going to zero volts as AC does. Any thoughts. Good luck getting DC through a transformer! I suggest you consult an introductory physics text. Jan Wolitzky, BTL Murray Hill, rabbit!wolit
lagasse@biomed.UUCP (Robert C. Lagasse) (05/31/85)
I have tried building a Jacob's Ladder using a high voltage supply of several thousand volts (using a flyback transformer from a T.V. set) to produce an arc between two metal rods that are placed in in "v" shape but do not touch at the bottom. One of the problems I have been having is that the high voltage arc wants to stay small in lenght. That is, it does not want to climb up the rods and lengthen and then break away unless I blow on the arc with an airstream (really!). What am I doing wrong? How do they do it in the movies?.... Any help greatly appreciated. Bob Lagasse @ MGH Boston
jp@lanl.ARPA (05/31/85)
I think that the flyback transformer is too low in power and does not heat the air sufficiently. I built a Jacob's ladder many years ago with an old neon sign transformer (15Kv @ 1KVA!!). Nearly scared my mother to death whenever I turned it on. For good reason too. Such a system is very lethal. Proceed with extreme caution. For an interesting effect I added, part way up the electrodes, miniature electrodes made of solder. The spark would reach this area and proceed up the solder electrodes to their end. The resulting heat from the stationary spark would then begin to melt the solder and the spark would climb back down to the regular electrodes and continue on its way. Neon sign transformers should be readily obtainable from old signs. Big signs tend to have big transformers, but the 15KV, 1 KVA was the biggest I could find in 1958. All of the transformers I found were made with a grounded center tap to limit the maximum potential to ground. It is not possible to connect two in series. Even if you insulated the cases the insulation from primary to secondary will not handle the voltage. Good luck, be safe, and don't scare your mother. Jim Potter jp@lanl.arpa
trebor@cuuxa.UUCP (gardner) (06/11/85)
In answer to the Jacobs Ladder puzzle, your problem is an inadequate power supply for the length of arc your trying to achieve. A television flyback for a color television set produces from 20 to 30K volts which will arc less than one inch with normal humidity. The reason the arc's length increases when you blow on it is the humidity of your breath increases the conductivity of the air through which the arc must travel thus increasing the maximum arc length. Trebor Rendrag.
JMSK@MIT-MC.ARPA (10/06/85)
From: Jacob Moskowitz <JMSK@MIT-MC.ARPA> You don't get enough current with the flyback to generate enough heat to make it rise. That's why they usually use neon sign transformers, which tyupically produce about 15-30 milliamps. Probably the Flyback puts out microamps (my guess) Good Luck.