# Need Help Building a Jacob's Ladder (Electric Arc)



## ActionJax (Dec 21, 2011)

Hello everyone. I'm starting my first project for the year. A "Jacob's Ladder." (electric arc)
I'm planning a Frankenstein Lab and as you all know, this is a MUST have. So I contacted a local neon sign maker and was able to pick this transformer. 








But I'm not sure its what I need. It was only $40.00. So I'm not out much cash. Can anyone let me know if I made a bad purchase?








I've seen other designs but nothing that have used this particular unit. So any help would be appreciated.








Thanks everyone.


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## Hippofeet (Nov 26, 2012)

Well. It's a bit gnarly looking, but it has a grounded secondary, so that's good news. The 30ma current is also good news. This may not instantly kill you, lol.

So get some 1/16th-ish steel wire (I have used brass no problems) and attach them to the two posts. You can wind them around, or clamp them, as long as they are secure. 

Have two straight sections of wire, keep them about 1/2 apart at the bottom, and then they should widen toward the top. If the top of the wires curl back down a bit, it can prevent a "pop" when the arc reaches the top, but it usually isn't an issue. Some Jacobs Ladders use a small fan pointing up to help gently start the arc moving up the wires.

Wire it up to a plug, on a 15 amp circuit, and see how it goes. Honestly, 15KV isn't going to make a monster arc, you may get a 10 or 12 inch ladder, past that, the arc will sort of fade out, in my experience.

Some things to NEVER DO :

Don't touch the wires with it plugged in. Even with the 30ma rating. It's bad juju. And a bad habit. I have shocked myself with an 18kv transformer, and luckily the current moved across my skin and not through,but it was still a funky feeling. 

Don't let the wires touch. Plugged in or otherwise. 

That's pretty much it. I think you should be good to go.


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## ActionJax (Dec 21, 2011)

Thanks Hippofeet. I appreciate all the advice. I've got to pick up some wire and copper and then we'll have a go. Wish me luck.


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## Hippofeet (Nov 26, 2012)

Good luck, man! 

Forgot to say, you may have to mess with that bottom distance between the wire where the arc will start. Not having done anything with your particular transformer, it's hard to say what distance will allow the arc to form. Maybe start closer, then widen out.

Have and fun and stay sort of safe! lol, I may make that my sig line.


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## deanhunt (May 27, 2008)

It's also a good idea to enclose the wires in a glass or plastic cylinder to prevent people from touching it.


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## corey872 (Jan 10, 2010)

I think you did OK. Neon sign transformers (NST) come in a couple of flavors. There are some around 9 kilovolt (kV) which run very small tubes and sometimes old cold cathode fluorescent lamps. An 'average' neon transformer is 12KV, but it looks like you have a 15KV unit - so a little higher voltage still.

The 30 milliamps (mA) is a bit on the low side, a 'standard' transformer might be around 60mA. For JL, the amperage will generally control how bright / fat the arc is.

For the wall plug anything standard should do. 15,000 volts x .030 amps = 450 watts on the output side. Figure maybe 500 or so on the input side to account for transformer losses, then go backward... 500watts / 120volts at the wall ~ 4.2 amps from the wall plug.

If you happen to get a later model transformer, sometimes they have electronic protection and/or control circuits...they would actually see the JL as a short circuit and may shut down, but this appears to be a big heavy older unit...stamped 1998, so should be OK.

So for construction, it's pretty simple, two wires in a "V" shape, insulated from each other and with a small gap at the bottom. I've actually used a couple sticks of copper water pipe before to make it a bit more 'showy' and they were...5-6 feet tall. Once the arc gets going, 15KV could probably span 4-5 inches pretty easily. Depends a lot on how much air current, humidity, etc there is when in operation. So the 'ladder' part can be most any length/height you want, but the overall span between the wires would likely be somewhere in that 4-6 inch range.

The 'tuning' consists of varying the gap between the wires, usually by bending the wires slightly. If the arc gets hung at the top, you want a wider gap. If the arc snuffs out half way up, you want it a bit narrower. If it arcs at the bottom, but refuses to climb, the "V" angle is too wide or if it refuses to arc at all, the bottom points are too far apart.

Safety - obviously make sure the thing is unplugged before making adjustments, or going near it, really. Don't touch while in operation,etc.

If you were looking to make a big project out of a small one, you could consider 'depotting' the transformer. Which means getting the actual windings and core out of that block of material. I've done a few which were potted in tar, yours has a brownish compound, so some additional experimentation might be in order to see if it can be melted away or if it's an epoxy type material. But if you were to extract the goodies, then you could do things like modify the voltage and current to give more power.

Lastly, if you're looking for 'the next step up' for the Frankenstein lab, you could use this NST as the cornerstone for a Tesla Coil (google). While the NST alone would be good for 4-6 inch arcs, the TC built from that transformer should easily do 4 foot arcs...so definitely a little more spark.

My Tesla Coil 'reanimating' pumpkin head scarecrow from ~13 years ago.










Either way, good luck and stay safe!


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## kentuckyspecialfxdotcom (Oct 20, 2008)

*Jacobs Ladder Safety*

I do like the neon sign transformers for safety reasons myself so I agree with cory872 but like deanhunt stated enclose the hot sections of live wires in something, plexi glass sheets, glass just something, anything.
While you will probably never make the ultimate mistake humans are unpredictable and not always educated.
We get stuck all the time making multiple Jacobs ladders with MOT's Microwave Oven Transformers because of tight budgets and need multiple ladders going for xyz desired effect and since the MOT's are extremely high amps and lethal we have to encase ours 100 percent in plexiglass boxes so no matter what happens, it's impossible for someone to get killed unless they bust through our plexiglass box while the unit is running.
Another good point about encasing in plexi glass is it also prevents a fire hazard as well so nothing can fall against it while in operation.
If there's one thing I believe firmly in is going over board on safety, you can never over do safety.


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## screaminscott (Oct 13, 2006)

Make sure you leave a gap or opening at the bottom of the enclosure to allow air in. The arc ionizes the air between the wires, then the heated air rises, carrying the ionized gas with it. It's this ionized gas that creates the lowered resistance and allows the arc to continue as the gap widens.

But if you don't let air in at the bottom, the heated air might not rise as easily and the arc won't travel up the wires.


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## HomeyDaClown (Oct 3, 2009)

15KV @ 30ma is fine for a power source. That's what's been powering mine for over 15 years now. I just built a wooden frame around the outside and added plexiglass sheets to the font and back to keep little fingers away. Used some sparkplug wire for connections & 1/2" copper tubing for the rods with short lengths of 1/2" pvc inserted from the sides to allow fine tuning for the rod spacing for the best arc and arc travel. The rods are 42 Inches which gives a nice long travel time for the arc. Often I get multiple arcs traveling up at different intervals.


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