There is an electric device I’ve always known as a “Jacob’s Ladder” though some googling reveals it’s more correctly known as a ‘climbing arc.’ It has two metal prongs and electricity arcs between the two, the arc rising up and new ones appearing lower down and climbing in turn. It’s looks neat-o and makes lovely buzzy zappy noises.
Now it seemed to me their major ‘function’ was to provide movie set dressers of the past with a shorthand icon that said “Mad Scientist at Work.” You see a Jacob’s Ladder, there is a mad scientist at hand. You see a mad scientist, there’s a Jacob’s Ladder in the background. They were nearly as closely linked as Siamese Twins.
What we got to wondering was, did the device ever have a real purpose? What would you use one for, other than a) the already mention movie set decoration and (possibly) b) to try to impress a classroom full of students that ‘Science is Really Neat’.
But it seems rather elaborate for a device that really doesn’t have a ‘genuine’ use. Was it a part used in larger machines to accomplish whatever? Like, oh, some sort of switch or timing control?
I put genuine in quotes, because one of the group suggested maybe it was used in some electric quack therapy, back when electricity was the latest thing and there were lots of people being ‘treated’ by giving them electric shocks.
(Hey, don’t laugh too hard, people are still buying magnetic-therapy devices.)
I don’t think so.
They are “scientific novelty” devices, which can be used to illustrate certain principles (like the breakdown voltage of air, and the characteristics of electrical arcs), but other than that, they don’t have a specific use.
There are other devices like this - the radiometer (the glass bulb with the spinning vanes) is one that comes to mind.
OK, I can think of one possible use - they can be used to create self-extinguishing over-voltage arcs. I seem top recall that some power substations used this principle to create a spark-gap which would strike an arc to protect from overvoltage (like a lightning strike), then self-extinguish once the overvoltage was removed. Circuit breakers now use magnetic and compressed-air arc extinguishers. It’s possible they used Jacob’s ladders in the past.
I have to post to this thread considering that I built one too.
To use someone else’s terminology, I used a “bigass” neon sign transformer.
When I’m not pursuing my “Mad Scientist™” profession, I set mine up (out of everyone’s reach) on Halloween to impress the kids (and adults).
Steve Martin in “The Man With Two Brains” references the climbing arc, when a scientist is displaying his laboratory. He says, where’s the test tubes? the beakers ? the bzzzz thing?
Like I said before, I think I have a 12K one at home (not sure, probably smaller). I just stepped out into my store to take a look at the transformer for another neor sign we’ll be getting rid of soon, 15K. I’ve always wondered what would happen if I put the secondary from the 12K into the primary from the 15K.
Lots of destructive arcing in the primary of the second transformer. It was designed with 120 V in mind; applying 12 kV to it will undoubtedly overwhelm the insulation. At the same time, the comparatively low impedance of the second transformer’s primary will overload the first transformer likely resulting in burning out the windings.
In ideal textbook world, you’d step up the voltage (and correspondingly step down the current) by the same ratio as it did normally. So if it’s normally turning 120 volts into 12000 volts, then it’d turn 15000 volts into 1.5 million volts.
In the real world, you’d probably burn something out. Lots of things can’t handle megavolts.
Just out of curiosity, what would I need to build a Jacob’s Ladder? I’m guessing a power source (like an outlet), a transformer, two metal rods and what else?
I think once I give a twenty minute speech to everybody on not touching the arc or the rods or anything else, I could really impress my family with one of these.
Oh, I would also keep an extinguisher on hand just in case.
That’s pretty much it. It does depend on how large you want it to be - a neon sign transformer or similar is typical, but you can make a small one with a solid-state inverter circuit. There are some good web pages for making your own that can be found easily enough.
