Jacob's Ladder





Introduction: Jacob's Ladder

About: Full time College student (Computer Science and Engineering Major) with a passion for building stuff with whatever is on hand at the time. Been tearing stuff down and putting it back together my whole life. ...
A Mad Scientist laboratory is not complete without a Jacob's Ladder. If you have always wanted one as a prop for Halloween or just to display, then this instructable will show you how to build one. It is very simple to make and you only need two components to make it happen.

Please vote for me for the Halloween Decorations contest.

If you wanted to know why the arc ends up going vertical instead of staying at the same spot, here's an explanation from Wikipedia.

"When high voltage is applied to the gap, a spark forms across the bottom of the wires where they are nearest each other, rapidly changing to an electric arc. Air breaks down at about 30 kV/cm,[2] depending on humidity, temperature, etc. Apart from the anode and cathode voltage drops, the arc behaves almost as a short circuit, drawing as much current as the electrical power supply can deliver, and the heavy load dramatically reduces the voltage across the gap.
The heated ionized air rises, carrying the current path with it. As the trail of ionization gets longer, it becomes more and more unstable, finally breaking. The voltage across the electrodes then rises and the spark re-forms at the bottom of the device."

This Instructable involves the use of High Voltage and if you are not careful, you will be seriously injured or killed! If you are not familiar with working with High Voltage, please DO NOT attempt until you research it and take all necessary safety precautions.

Make sure to keep it away from everyone that views it by placing it in a clear housing or placing it in an area where it can be viewed and NOT touched. 
We place ours on the roof of a treehouse during Halloween so that its away from everyone that comes through our haunted yard.   

Step 1: Materials and Tools

This has got to be one of the easiest instructables around because it only requires two components and a few hand tools.

  • Neon Sign Transformer (My transformer's specifications are 60Hz, Primary Voltage 120, Secondary Voltage 9000, 146W, 1.28A, 30MA)
  • Wire Coat Hanger 
  • Sand Paper
  • Wire Cutter
  • Two Pliers

The Neon Sign Transformer can be found on Craigslist or at a neon sign shop. Expect to pay around $50 to $150 for one.

Step 2: Cutting the Wire to Form the "V"

The V is made out of the wire coat hanger that you have laying around. Take your pliers and try to get the coat hanger as straight as possible. You can even use a hammer and anvil or concrete to try and get it as straight as possible. The straighter the wire, the better the effect. 

Traditional V-
This is the way that most Jacob's Ladders are constructed. First you take your straightened wire and bend it exactly half way. At the half way point, you are going to take your wire cutters and cut it there. Now you have two pieces of coat hanger wire. Coat hanger wire usually has a coating on it, so next you are going to take your piece of sandpaper and try to sand as much of that coating off as you can. 

Step 3: Attaching the Wire to the Transformer

All transformers have two output terminals on it. They both may be on one side of the transformer or they may have one output on opposite sides of the transformer. My transformer had both output terminals on one side so I will explain how to bend the wires for my style transformer.

Make Sure its Unplugged

Since the output terminals had nuts, all I had to do was bend the coat hanger wire into an eye so that it slips onto the bolt. I then had it go straight up from the terminal before it was bent towards the other output terminal. Once I got it as close to the center as possible, I bent the coat hanger wire straight up and into one half of the V. I did the same to the other terminal's wire.

The next part  can be very dangerous if you don't follow precautions. 

It is time to tweak the V for the best performance. If its too far apart at the bottom, the arc will not form. If it's too close then the arc will just stay at the bottom. If it's too far apart at any part before the top of the V, the arc will disappear before the top. The goal is for it to perform reliably and to travel all the way up the V until it breaks at the very end of the leads. 
You will need to plug it in and see how it performs. Unplug it and adjust it. Just make sure to unplug it and be prepared because the leads can get very hot from thearc. Adjust it as needed until your satisfied with the result.

Step 4: Enjoying Your Work

Plug in your Jacob's Ladder into an extension cord and place it somewhere or in something where it can be viewed and not touched. For best effect, use it in a low to no light environment and block it from wind as the wind will not allow the arch to travel very far. 

Remember that this is a dangerous toy and can cause real harm to anything that it touches. Use it safely and enjoy the expressions on your spectators' faces as they go past this device in your haunt.

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19 Discussions

Also testing 15 cm away so that equiv to 233 volts per meter total exposure for 60 minutes.

Data info.

3500 volts per meter for 60 min on clover: Death.

1167 volts per meter for 60 min = Death.

566 volts per meter = death.

410 volts per meter = ????????

The link did not work so here are some pics...


would hooking up an old speaker/hard drive/random dc rectifier power cord to a little step up module like this work?


I have access to several different "ratings" of neon sign transformers. Are there any that cannot work for this or that are not recommended? Or is it ok to use whatever?
just curious.


1 reply

Smaller transformers may not have enough power to create a good jacob's ladder. Higher voltage is better.

I like the idea of using copper for the colors, but you can also use a lighter guage wire for smaller transformers and greater movement on the big ones. I have used the wire from marking flags you see along the road to mark buried utilities and stuff and you can buy them at a farm supply store for about 10.00 for 100 or so markers. get the longest ones, as they are usually the same price, and the wire can be used for many, many projects, as it is a very stiff wire that can be used for linkages, etc.

When the thinner guage wire is used on your ladder, the wires will move in and out more and give you more or different movement of the arc's.


Also, if you substitute the two wires, use one brass gas welding rod for one side and one copper coat gas welding rod for the other side. You will get a green blue spark. Still use plenty of ventilation. Avoid at all cost, getting too close. I prefer using the 12-15kv neon sign transformers my self. The 15ma ones work great. 30ma is better, but the cost goes up significantly. I used to use these and tesla coils in a haunted house for halloween. Another fun project that I might put on here later, using flourescent tubes, you can have ribs of light moving up and down the tubes.

I never get tired of seeing these. Thanks for the instructable!

Please swap coathangers for aluminium or steel wire. Regular coathangers are often zinc plated.
The sparking will release zinc oxide particles. Breathing them is not so good for you.
The zinc shakes is a problem for people welding galvanised steel.

Also be aware that sparks create ozone. If you plan on leaving it on for extended periods ensure there is plenty of ventilation.


If the case that encloses the transformer is ventilated that too creates ozone of a smaller magnitude. High voltage magnetic fields create ozone.


Don't mean to be a buzzkill...it's just research I've done in the past.

1 reply

Yea. I forgot to add that about ozone. It can also cause radio interference.

Always wanted to build one of those, but suitable Transformers seem hard to come by here in the UK. You would not BELIEVE the prices the neon sign people want to suck out of your bank account to let you walk away with their junk.

One might almost think I wanted their PERSONAL "Junk".

I'm not an expert on Oil Burning heaters either, but since they don't seem to need extinguishing and relighting (not sure if that's a requirement here) they don't seem to have big transformers either.

It should be possible to do with a modified Microwave transformer, but I'm not sure I'd know exactly how to go about it.

1 reply

You can check ebay, electronic surplus, electronic supply, and appliance supply stores too.

If you can't find one from those sources, you can always build a transformer yourself. This video on youtube was done by some guy in Colombia so the English is off, but it gets the point across.


Just remember to make a step up transformer. I think the video shows a step down transformer.

Microwave oven transformers can be used, but I would not use them because they are very unsafe. This site explains how to build them and what components should be used. http://www.repairfaq.org/sam/jacobs.htm#jlwnm

used to make tons of these with my dad, still great to see!

Rimar2000 has a great way to straighten wire. https://www.instructables.com/id/An-easy,-cheap-and-efficient-way-to-straighten-and/

1 reply

Thats a really good idea. I've used it to make a wiring harness, but never thought to do that with it.

Besides a Neon Sign power supply, you can also do this with a ignition transformer from an old oil-burner from a furnace. Many years ago, we had one fail on our furnace, and the tech who came to service it, said he had seen others do it with old ones.. the gap need be about 3/4 of an inch apart at the bottom, and can extend outward to about 4 inches, as high as 3-feet _\ /_ style wires.
As with ANYTHING with voltages above 60V, take great care never to make contact with the output of the transformer, or the wires, or results could be FATAL! (this coming from receiving a good 8KV shock across my arm.. swung around, and it knocked me to the floor! I was just plain lucky!!!)