Helical Jacob's Ladder





Introduction: Helical Jacob's Ladder

Helical Jacob's Ladder Project:

  • experience level: beginner
  • parts needed include: transformer, power cord, bare wire, wire nuts, wood block, wood screws, wooded dowel and a nail
  • tools needed: screwdriver, wire stripper, wire cutter, and drill
  • Safety notice: Always unplug or isolate a device from its power source when servicing!
  • Perform these tasks under the direct supervision of a parent or a trained adult!

Step 1: Step 1: the Transformer

All transformers run on ac current. The transformer has three leads coming from the primary coil and two from the secondary. Of the primary: one is the hot lead, the others are neutral and ground. Strip the wire ends about three fourths back from the tip. Connect the hot and neutral wire to the power cord using wire nuts connect the ground to the base of the transformer. Strip the bare ends of the secondary wires and connect them to the bare wire (we used electric fence wire).

Step 2: Step 2: Wood Block

Mark and drill pilot holes into the wood block to mount the transformer to one side. Screw the transformer down to the wood block. Then drill two holes approximately one inch apart on smaller piece of wood and run the bare wires through the holes. Mount to the open side of the block. Connect the hot lead from the secondary to a bare wire and Mount the wire to the block with a screw. Take the other bare wire and connect one end to the common ground. From the ground post, run the wire to the second hole and mount with a screw.

Step 3: Step 3: the "Jesus Stick"

Take a small to medium size nail and push or pound it into end of a dry wood dowel. The transformer used above is relatively small and wont be able to create the arch without a little encouragement. With a larger transformer, the arch will jump between the two bare wires without any assistance.

Step 4: Step 4: Powering Up

Plug in the transformer to any standard 120 volt outlet. Use the nail end of the "Jesus stick" to cross the between and touch the bare wire leads at their base to create an initial arch. The arch creates heat and ionizes the air around it. The heat will rise pushing the arch up to the top of the wires.

Step 5: Step 5: Experimentation With a Helix Design

Unplug the transformer from the outlet. Take a piece of small diameter pvc and place it between the two bare wires. Twist the bare wires around the pvc maintaining an equal distance between them. Then remove the pvc. Plug in the transformer and use the "Jesus stick" to cross the leads again to create the arch. Notice the way the helix slows down the travel time up the wires. This is caused as a result of having less heat directly underneath the arch.

Step 6: Step 6: Additional Modification

Unplug the transformer once again and remove the current leads. Take additional bare wire twice the length of the original wires. Fold the center of one length and place it into the chuck of an electric drill, place the two free ends into a vice. Twist the wires until they are tight. Repeat this again with a second length of wire. Mount the new twisted wires in place of the original helix wires. These heavier duty wires can be modified to a helix or left upright as shown above. Plug in the transformer again and enjoy.



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    Beginners please read this:

    Jacob's ladders are great fun. But microwave oven transformers are not current limited and can easily deliver a lethal amount of electricity. And for extra fun you don't even need to touch them to kill you.

    The voltage is high enough that it can "jump" / arc off the wire onto any nearby conductor, such as your skin, and down to ground via your heart and muscles. Arcing is more likely to happen on a sharp edge such as you might find at the very top of the ladder which may be close to your groin or the head of a nearby child.

    This may result in A Bad Day.

    This project is easy to construct but if you don't know what you're doing you or someone near you can die instantly. If you want to play with high voltage, then start with a project that makes nice sparks but with very very low current

    For anyone that wants to know how an MOT works, check out this link

    " http://www.microtechfactoryservice.com/doubler.htm... "

    With that beefy diode in the sercut it becomes effectively a voltage doubler,

    after the voltage transformation. It's so cool how it works.

    The tut. I used to build my JL called it a chicken stick.

    Been there done that. I built one 4 feet high using a 15KV 60mA "neon-sign" transformer. I use #12 solid bare copper wire. The helix is about one turn per 6", with 1 inch spacing between the wires throughout most of the length. (Your helix is a bit steep, that's why arc "hangs up"). At the bottom, the wires are 1/4th inch apart tapering to 1 inch over a 2 inch length. At the top, the 1 inch spacing tapers to 3 inches to break the arc. There is no helix in the tapered regions. The entire assembly is enclosed on a 6 inch diameter glass tube (without the tube, the Jacob's ladder is extremely sensitive to air currents in the room. The tube also provides part of the protection of all the high-voltage lines). The hard part is supporting the wires in a uniformly-spaced helix. Every 6 inches I had side wires (brazed onto the main wires with no protrusions in the inside of the main wires) fastened to rings of circuit board, which just slide into the glass tube. All wire ends are rolled back or filed smooth.

    If the tube length is set to be acoustically resonant at 120Hz, the arc sound is awesome!

    Comment for DavidJ2: microwave transformers are current limited, but the current is too high and the voltage is too low (that's why wire melted in video, and Jesus stick was needed for starting). The magnetic core shunt between the primary and secondary provides the current limiting. Of course, all the high-voltage lines need complete covering, and an operator needs to be present to supervise running. Running it open as done in the video is dangerous!

    Comment for dick55: the capacitor is removed from the circuit, so there is no danger after the transformer is unplugged.

    For Laral: Comment about using lower current transformer "to make it safer". A Jacob's ladder relies upon having a considerable current to deliver enough power to the arc to heat the air and make it rise, and to exploit the "negative resistance" of the arc. This allows the arc to traverse the wider-spaced area (at low currents, the arc will "break" and restart after going up a little). So you can't "make it safe" and also make it work. Safety must be gained by preventing human contact with the live parts by appropriate covers, not lowering the current. The arc is also a fire hazard.

    3 replies

    Gee, you could've fooled me, and the thousands of people who have made much better performing Jacob's Ladders using SAFE 10kV oil transformers. Mine used 3 ft. electrodes. I could easily have used 6 ft. ones if I enclosed it in a 6 ft. plastic tube. You really shouldn't make statements like that concerning things you know absolutely nothing about. It's the high voltage, not high current, that makes this work. 10kV x 23mA = 230VA. That's a lot of power.

    It IS the high current that counts! Air has a negative resistance. The more current that flows, the less voltage required to maintain it. The whole principle that makes a Jacob's ladder work is that the arc strikes at the closest point, at the bottom. As soon as this arc strikes, the voltage sags under the load, as provided by the characteristics of the transformer, combined with those of the arc, to below the STRIKING potential at the bottom. This prevents the arc from re-striking at the bottom as the arc travels upward (despite being longer), driven by the heated gases buoyancy. When the arc reaches the top, further spreading causes the arc to break. The open-circuit voltage of the transformer re-appears, and re-starts the arc at the bottom.
    To make a really tall Jacobs ladder, the electrodes should be close at the bottom, tapering out to a long parallel run for most of the length, then tapering again at the top. For a 15KV 30 mA transformer, starting gap is only 1/4 inch, taper over 2 inches, to a parallel run 1 inch apart, and top spread to 3 inches over 6 inches. I don't know what current level the "SAFE" transformers produce (I have never had access to "SAFE" transformers). But 30 Ma is certainly not "safe". You need a minimum of 30mA to get an arc to stably run to the top without breaking and re-starting at the bottom repeatedly.

    To be safe from an shock hazard standpoint, the current would need to be limited to way less then 1 milliampere. A Jacob's ladder will not function at this current.


    That's totally contrary to my experience and that of others I know. 23mA is more than enough, as I said, based on my experience. Sure a 60mA 15kV neon sign transformer gives a thicker spark, but it is not at all necessary. Obviously 'safe' is a relative term. Neon sign transformers have a shunt that limits their current to 30-60mA, and sometimes 120mA. Those are the limits that the manufacturers consider 'safe', as in 'not lethal'. You don't think manufacturers would risk a law suit do you? Compared to the lethal shock you'd get from two microwave transformers in series, the jolt with the accompanying 'burn' from even a neon sign transformer is extremely safe. And 23mA @ 10kV is mild even compared to that.

    You need a particular type of transformer....
    Wondered why the one out of my 'phone charger didn't work!

    Seriously, sorry to say, but many 'instructables' fail because the author assumed something. I this in this case, automatically assuming we knew what a microwave oven transformer looked like.
    Golden rule is to silently get one of your non-nerdy friends to review first. And that means SILENTLY, without giving slight hints. Preferably while the author is in another building.

    The many comments below, and the previous one by Bongomikey in particular, warn how LETHAL an 800W High Voltage transformer can be.


    I don't know where this capacitor is but even after unplugging it may well be storing powerful high voltage until it bleeds off. And how long does it take to discharge? At least use the Jesus Stick to create an arc at the bottom of the ladder after unplugging and then short it out to fully discharge the capacitor. If you do see an arc then you should be bleeding off high voltage.

    Even so, I would be much more comfortable measuring the HV with a HV probe multimeter. But in truth I would never even subject myself to the probability of a lethal shock knowing how likely accidents are.

    1 reply

    the HV capasitor have always a 20MOhm resisor in parallel. U(t)=U*e^-(t/(R*C))
    --> not dangerous after waiting 80 seconds :)

    My oil furnace transformer is 10k volts

    1 reply

    Oh, OK. Is it rated 23mA?

    Your WHAT is 10kV? How many amps?

    Editor PLEASE this is far too dangerous a project to show to people who do not understand what 800W of high voltage will do. It is LETHAL!

    Careful with a microwave transformer....they are capable of upwards of a half amp..with 2000 volts, it could easily kill you....you are better off with an oil furnace or neon sign transformer...they are current limited aoumd 0.030 amps.....

    I noticed in the first picture that the secondary coil appears to have the three wires. This makes sense because I assume that one is a center tap. Either way, you clearly have your electric cord soldered to the two wires on the primary side. In your instructions you say that the side with three wires is the primary coil and yet the power cord is soldered to the other side. The side you have the cord soldered to is clearly the primary since the wound wire is larger than the other coil. Anyone that knows about coils would know that on a step up transformer such as this the primary will have the larger diameter wire. Great job on the build! I think I will build one now since I happen to have a microwave transformer also. I have a much larger transformer as well! Hmmmm...maybe I'll get the courage to build one with that transformer afterward. Thanks pal!!! You inspired me.

    If you don't have fairly extensive experience working with electronics, plus a background in physics, you really shouldn't mess with a project like this. High voltage electricity isn't a game, nor is it amusing or fun. It's a sure ticket to the afterlife.

    Labeling this as "beginner" is irresponsible and just begging for trouble. It's easy to build, true. It's also easy to step in front of a bus.

    Perhaps you think I'm being a bit unkind, but having witnessed the many crazy and insane things untrained people do with electricity, I feel that we should try to avoid adding to the body count.

    OK, if the input to the transformer is 120 volts, what is the output? You are missing a key spec.

    From what I see, the Digital Power Communications transformer OBJY2 DPC-R is an 1100 watt microwave transformer (I see one on eBay for $30). I don't see any spec for the output voltage on a quick search. Anyone know what the output voltage is?

    Note: You shouldn't have to manually start the arc. If you closely space the electrodes at the bottom, it will be self-starting. You can bend in a horizontal V on each electrode to get close enough.

    Although this an interesting variation on the Jacob's Ladder, your choice of a microwave transformer is very dangerous. It probably has no current limiter so could be lethal if anyone touches the electrodes. A much safer, though not completely safe, transformer is an oil burner ignition transformer which has a shunt to limit the current to a few milliamps. It is the standard transformer used to make this device. If you space the electrodes properly, you will get good arcs. As I recall, they output 3000V. You can get these transformers for free or for a few bucks from any oil burner repair service.