Original poster: David Speck <dave@xxxxxxxxxxxxxxxx> Jim,It's my understanding that the arc length of a JL is primarily dependent upon the current available, not the voltage. Once the arc is established, the voltage drop across it is only a few hundred volts, if that much. Supplying it with more voltage doesn't do anything to increase the arc length. Other list members have reported that X-Ray transformers have made disappointing JLs, because they can supply relatively little current.
How much current is your current pole transformer rated for? If you go for a higher rated transformer, and can supply it with enough current, then you should be able to get longer arcs. However, JLs are hungry beasts, and you do need a lot of current to drive them. Ed Wingate's JL draws a maximum of nearly 100 amps at 240 VAC. I'm not completely certain, but I think he was driving it with at least a 10 or 15 KVA transformer to get about 24 - 36" arcs at the final break.
I'll have to dig through my reference books about the GE flaming 20 foot three phase arc display at the 1939 NY world's Fair. Although they were billed as "Million volt" transformers, the leakage inductance of the transformers made them function like giant self ballasting NSTs, according to the retired GE employee I once talked to about them. They were driven by big motor gensets onsite, rated for a great many horsepower. It was the high current available to them that made the spectacular continuous arcs.
Dave Tesla list wrote:
Original poster: "Jim Mora" <jmora@xxxxxxxxxxx> Hello List,I am considering purchasing a Big box x-ray transformer, somewhere near 100kv at >150ma single phase 240v 60hz for a large Jacob?s ladder. What has been anybodies? experience with these? It is presently DC out but I would remove the diodes and filters and put a flat plate on top with (2) 14,400v horns on it. Evidently others are doing this without arcing to the grounded case.Here?s the question: how big of arc could I expect to draw on a dry, windless night. I have not been able to get much more the 12-14? with our usual 14400 driven hard.?A bit off topic, but hopefully of interest. Thanks, Jim Mora