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Registered Member #498
Joined: Sun Nov 19 2006, 06:00PM
Location: Bay Area
Posts: 19
Yesterday, I finished my first Jacob's Ladder! It's made out of two coathangers, an NST, some nails, and a blovk of wood. It has two sets of electrdes, so incase I can't get the main "ladder" working, I can just have a normal arc.
so far, I've fried several thin wire sections from a stranded wire (makes nice aluminum globs on the end), a bay leaf, and part of a tofu dog. My only problem is that a lot of the time, the arc from the ladder section doesn't "catch" even though they're about a quarter inch apart. This is a US transformer, so it's 15kv and not 10kv like the UK ones.
(PS: How long can an NST run shorted (with no load) before it becomes irreversably damaged? )
Registered Member #192
Joined: Fri Feb 17 2006, 03:08AM
Location: Canada
Posts: 44
I've experimented with JL's too. See a post I started (link below), further down the thread is a post about a Gabriel Electrode. This is a third electrode or point inbetween the two JL rods, this helps start the arc.
At 15 Kv you shouldn't have too many problems starting an arc. Make sure there is a sharp bend in the rods where the arc should start, a 1/4 inch gap should be good.
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
You just need a little breakout point at the bottom to start things. Sparks jump further to sharp points. Set this by experimentation and have it adjustable preferably. Just be super careful not to adjust it while it is live. Always unplug it if you are going close, don't just rely on a swich. Have a bright light to indicate the on state and work with one hand in your pocket when you can. Make a point of checking with a screwdriver that it is not live. This is not as important for a JL but is for capacitor devices.
"A Gabriel electrode used to make the gap at the bottom of the vee less critical. In a normal Jacobs ladder there is no third electrode and it can sometimes be difficult to balance the shape of the vee for the best results.
"If the base is too close then the arc won't rise all the way to the top of the ladder because it's easier just to jump the gap at the bottom again. If the base is too far apart then there is the serious risk of the arc not striking at all meaning that the unit will look as if it's switched off when in fact the full voltage is across it. With the limitation of a 10kV transformer I found that the gap was too critical and I designed the Gabriel electrode to solve the problem.
"It allows the gap to be much wider than normal, but allows the ionisation of the air via two 1 Megohm resistors that make the middle electrode into a semi desireable path for the arc. When the unit is starting an arc it initially jumps over between the middle electrode and the opposing electrode which ionises the air and then pulls the current limited voltage down on the middle electrode. The arc then jumps across the remainder of the gap. It works very well."
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:D My first HV experiment (Jacob's Ladder)
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