Jacob’s Ladder Using A 10kV Oil Transformer

Jacob's ladder using an Oil Furnace Transformer

Jacob’s Ladders are a staple experiment in any self-respecting mad scientist’s lair — err, a hacker’s workshop. And why not? High voltage, arcing electricity, likely more than enough to kill you even — brilliant! But in all their awesomeness, Jacob’s ladders really aren’t that complex.

In [Kevin Darrah’s] latest tutorial he shows us how to make one out of a transformer taken from an oil furnace. Why exactly does an oil furnace even have a high voltage transformer in the first place? They’re actually used as the ignition source, like a pilot light!

The one [Kevin] has is a 110VAC to 10,000VAC transformer, which puts out about 20mA (probably enough to kill you). And to turn it into a Jacob’s Ladder, you’ll just need a two long stiff wires (copper is a good candidate). The wires are closest at the bottom where the transformer can easily arc — this arc then ionizes and heats the air causing it to rise, carrying the arc with it. As the arc continues up the ladder it gets longer and longer as the wires become farther apart, becoming more and more unstable until it breaks. When this happens the arc forms again at the lowest point of resistance — the bottom.


It’s certainly a fun experiment when done properly, just make sure you are being safe when working with any high voltage equipment — not like this guy who used a similar transformer to electrify some home-made wolverine claws.

21 thoughts on “Jacob’s Ladder Using A 10kV Oil Transformer

  1. I’m working on one of these right now. The enclosure is really what makes it. I have an ancient western electric box mine is going into. A friend suggested a safety screen since this will be a prop for halloween. I think stainless steel may be a better material. I envision the copper oxidizing over time.

  2. They are so fun to make and play with. I’ve made one out of the newer oil furnaces also,they have a solid state high voltage power supply(17000v at 20 cycles) and the sound they make are a deeper sound. Years ago I took a 1 ma panel meter and made a volt meter to measure voltage out of the 10000 volt transformer. It worked so well my company had me make one for them.


  3. I did the exact same thing in my college apartment in ’98. My drunk friends would take turns smacking it bare handed to see who could do it the most. Later that night I rigged it with a switch to my bedroom door and used it as the ignition source to a small propane charge (plastic lemonade container filled with propane and air) which alerted me to the approaching shaving cream attack.. Dodged that one and scared the crap out of everyone at the same time. :) 16 years later and I still use the same transformer (or a similar one from a neon sign) whenever I need a quick 10,000 volts.

  4. I built one too in 6th grade for a science fair. The oil burner transformer was in a wooden box with the electrodes sticking through the side. Then two 1/4″ brass rods were made connect to the studs.

    These things create a lot of ozone, NO, and NO2. None of which are good to breathe. Mine had the electrode area enclosed in a glass box.

    No, there is no emp and no significant emf. This is line frequency so there is not much to worry about. 20ma can kill you if you are pretty unlucky, but these are shunt current limited transformers.

        1. So I am not sure how well it approximated a spark gap transmitter. They are very interesting but we all know the FCC would frown upon their operation. I havea a feeling they are noisier since there is a discontinuous arc.

      1. Not really. Typical spark gap transmitter use some sort of capacitor circuit to create a tank circuit. Just a 60hz arc does not create much. If so you would have all sorts of problems with neon signs and any place with an oil furnace.

          1. None of which has ever fried a computer. If you have an AM radio you might hear something. The EMI is not significant enough to effect anything else. It is not until you get into stuff like the high-freq units like you find in TIG machine where you need to start worrying, those things crash computers and cnc machines all the time.

          2. I can’t reply to yours macona because the thread has gone too deep. I am a licensed amateur radio operator, and all of those devices cause enough noise as to violate FCC regulations for unintentional radiators. I’m unsure where you’re making the leap to frying a computer as that was never mentioned by more, nor is it my concern. I am however concerned with being unable to use licensed portion of the RF spectrum because some kid followed the directions he found on this website and is wiping out the HF bands for his entire community. That bothers me, and articles like this need to educate readers that this is a real issue that they need to be cognizant of, less they find themselves facing FCC inspectors and a notice of apparent liability.

  5. Did this a few years ago with a neon sign transformer, 35kV @ 20mA. Was doing some crude noise immunity testing on a pair of AES audio chips (tx on one end, rx on other) by wrapping 50 feet of 3-conductor cable (terminated by XLRs plugged into the tx/rx sides) around the ladder and flipped the switch. Got one chip to explode, and got a few others to latch up and die.

    I had some thin metal rods, slightly thicker than coat hangers, mounted to a couple of 2×4″ planks so that I could adjust the gap. Did the initial setup, flipped the switch and nothing happened. Wasn’t thinking (it was late) and tapped one of the planks with my foot. Got zapped HARD. That AC went from the rod, through 2 feet of wood, through my shoe and sock, up my leg, down my other leg, through my other shoe and sock, and into the 1 inch concrete floor, and into the earth. 35kV aint no joke. Scared the SH!T out of me.

  6. Companies which sell oil furnaces are always getting the old ones back. I have had very good luck calling them up, and if they have one or two, getting there pronto before others beat you to it. In a short time, you can collect all of the ignition transformers and air blowers that you can want.

    10 KV, even supposedly current limited, is truly DEADLY! Just grab a wire in each hand, and the current path is straight through your heart. You can stop your heart in just a few seconds. The best protection I have found is to put Jacob’s Ladders way the hell out of reach, with skull and crossbones signs on all sides.

    Not to mention the obvious, but these things are called IGNITION transformers and they can make anything flammable CATCH FIRE!

  7. Way back in school, we made one out of a 65 kV sign transformer. We were afraid the voltage would be dangerously high, especially considering we were drinking and we figured we’d bump into it. Instead of powering it with line current, we hooked the primary to a 1.5V “D” cell in series with a mechanical buzzer. It made sparks over a short distance, but wouldn’t carry up the ladder. So we plugged it into 110VAC anyway. Nobody died.

    1. That seems pretty selfish of you: Nobody is allowed to experiment – to learn – anywhere – so that you can can have all HAM frequencies available to you for YOUR social-networking hobby? Hrrrrrmmmmph! Will you stop broadcasting when the law prohibits it?

  8. “Exposure to an arc-producing device can pose health hazards. In a closed space such as a classroom or home, the continuous arc formation of an open-air Jacob’s ladder will ionize oxygen and nitrogen, which then re-form into reactive molecules such as ozone and nitric oxide. These free radicals can be damaging to the mucous membranes of people near the spark gap. Plants are also susceptible to ozone poisoning.”

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