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.

Materials-

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

Tools-

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.