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As soon as the testing was finished and I got the idea to try to make a Jacobs Ladder. I put some small wires on the coils and set the coils to parallel configuration. The wires were about 1/4" apart at the base of the V shaped ladder. They were about 2" apart at the top and the length was about 5". I set the setting selector to 4.5 and powered it up. There was no spark. I increased the setting to 6.0. Still no spark. I began to wonder if I had burned the coils out during testing.
I raised the setting to 7.5 and it began to operate. A bright yellow spark that looked like the flame from a butane cigarette lighter set wide open on a hot day began to climb the ladder. It was exciting! The arc climbed the ladder at the rate of about once per second. It had a soft sound much like the sound of alternator whine in a car radio. The arc was about 1/4" in diameter and took on an upside down V shape as it reached the top of the ladder. It was perfect!
It worked so good that I decided to try to make a bigger one. I got a 3' piece of piano wire, broke it in half and made the ladder of it. The ladder was now 12 ½" tall. It was 1/4" apart at the base and 1 ½" apart at the top. I set it up as before and powered it up. It did not work. I raised the setting up to 9.0 and it still did not work. Again I wondered if I had burned out the coils.
I then closed the gap at the base to slightly less that 1/4" and tried again. It began working at the 9.0 setting. The arc flame was still as big and bright as before but it could not start across a 1/4" gap. This seemed rather strange because that was the same setting that had jumped across a ½" gap. It was possible to see tiny blue coronas discharge from the upper tips of the wires when there was no arc. The coils and the motor were getting hot by that time so I shut it down and thought about it a while.
A 3 foot Jacobs ladder in operation
The conclusion that I reached was that the long wires of the ladder were capacitive. As a capacitor they were absorbing the charge from the coils and thereby preventing the peak voltage from being developed. That is why a gap slightly smaller than 1/4" was the biggest gap that the ladder could start with even at the higher settings. Once the arc started is was a low conductance path that allowed the arc to have a high amperage.
The high amperage heats the air extremely hot. The air begins to rise immediately and takes the arc with it. A slight breeze is all it takes to move the arc around as it is rising. The key to making a good Jacobs Ladder is not the voltage available. It is the power available to make the heat. The maximum power that this power supply can deliver before the motor overloads is roughly 200 Watts.
The high capacitance of the Jacobs Ladder suggests that the long wire rhombic antenna will also be a highly capacitive load as an antenna. It has a similar angle between its elements. The antenna is not supposed to have an arc between its elements as the ladder does. It would be little more than an RF noise maker that would scan all radio bands as the arc climbed the ladder if it did.
The operation was still erratic. Sometimes the arc would start but it would not rise. The cause was that the wires where the arc started at became so hot so fast that it was a lower conductance path than the hot air rising from it. They got red hot and probably would have melted if they were copper. The solution was to make the bottom ½" of the ladder parallel with only a slight spread. That served as a launching point for the arc.
Having set the ladder up this way it worked well consistently. When it starts up and is cold it is necessary to set the regulator to the 12.0 setting to get it started. As soon as it starts the setting may be lowered to 7.5 for continuous operation. If you try to do this yourself do it outdoors. I found that the ladder and the alternator cause ozone poisoning very quickly. It takes a lot of ventilation, not just a little, to prevent that.
The Jacobs ladder is somewhat difficult to photograph. The arc travels up the wire at about 1 pas per second. That is about the same speed that the computer camera scans frames at. The result of computer photography appears to jump back and forth erratically instead of the nice smooth passes that it actually makes. The sound is a soft zing vyiiiing sound that sounds much like alternator whine in a car radio.
A regular camera was used to make the photos seen here. In the third shot you can see the illumination level from the arc was affecting the cameras automatic light adjustment. In the fourth picture the arc went behind the spreader instead of in front of it. Of course this was not known until the pictures were developed and the ladder disassembled. The spreader is merely a piece of electrical tape folded in half. Without it the wires are attracted to each other. Without the spreader the wires wobble more with each arc until they hit each other. The gap between the wires at the spreader is 1 9/16".
