Introduction: Mad Scientist's "Jacob's Ladder" Lightning Prop

You've seen Jacob's Ladders in Frankenstein movies: you know, the gizmo with the two antenna things sticking up, and a bright arc of electricity rising between them, and making that wicked crackly sound. Nothing says "Mad Scientist" like this thing... and although it can be dangerous if you're not careful, it's actually not that hard to build. At its heart, it's really just a big ol' neon sign transformer (about the size and weight of a car battery), and a couple of thick wires... the rest is just safety stuff; housing, a switch, and insulators to make sure the spark only happens between the wires, and never travels through someone's body.

Yes, safety is incredibly important with one of these things... it's a lot of voltage, and could actually be fatal if you let it pass through you. So DON'T let it pass through you! I'll be mentioning safety precautions as we go, but the biggest one is this: BE CAREFUL. Never touch any part of the device while it's running, and double-check, triple-check, quadruple-check that it's unplugged before you approach it. Just because it's not sparking doesn't mean it's safe!

Other than the basic transformer, wires, and some safety stuff, it's all just window dressing... You can put a lot of knobs, dials, pipes and such all over it -- I also added a little plasma lightbulb which radiates pink lightning from its filament to its glass bulb (I saw a cool prop where someone had done that, and decided to borrow the idea).

Much of what I did on this prop was unique to my particular set of parts; as you look around for your own pieces, you'll probably need to adjust a lot of things, and improvise. But that's a good thing; in fact, it accounts for about 90% of the fun!

Step 1: Find a Transformer

You need a neon sign transformer... But newer neon signs don't have the right kind of transformer, so you have to find an old used one. Try looking in these places:
  • a neon sign repair shop
  • Craigslist (that's how I found mine)
  • a used electronics shop
Be sure to let them know that you're planning to make a Jacob's Ladder; they'll most likely know exactly what you're up to and point you to an appropriate one. And they'll probably give you some great advice as to how to get the most out of it without electrocuting yourself.

I got mine from a guy who WAS going to make a Jacob's Ladder for Halloween, but then decided he didn't have enough time this year.  It's pretty beat up, but I like it.

Step 2: Make a Plan

Here's what I knew, starting out:
  1. The transformer is big and heavy
  2. The transformer is dangerous, and needs to be kept far from people's touch
  3. The spark is dangerous, and needs to be kept enclosed so nobody can touch it
  4. Should look like some kind of old lab equipment
I must have wandered through a dozen hardware and thrift stores while formulating my plan... I really enjoy looking at things and imagining using them in a way that was never intended. My favorite haunt was the 99 cent store, because I could load up a shopping cart full of random items without hardly worrying about the cost.

I needed a couple of critical parts before I could really begin to plan the details... first of all, I needed a big glass tube within which all the sparking would happen, out of reach of anyone's fingers. My wife suggested a big vase from a florists supply shop, and sure enough, I found the exact thing I was looking for at a flower place called "Aldik" for about $50: a 7" diameter cylindrical vase, 27" tall. Pricey, but it's the single most important safety item, so I went for it. (Later, I discovered a slightly shorter -- but otherwise identical -- vase at Michael's for about half that. Dang.)

For the base, my first plan was to use a window box I had found at Orchard Supply Hardware, which (if used upside-down) had a nice trapezoidal silhouette. I thought maybe I'd use two, one upside-down and one right-side up. So that's what I drew first, along with an idea for incorporating a hand-truck (dolly) into the design so it could be moved around easily.

Step 3: Revise Plan

But then I realized I really needed a much bigger box for safety... Because I wanted plenty of space between any metal side handles and the electrodes coming off the transformer; I could all too easily imagine someone grabbing both handles to move it while it was plugged in, and creating a very nice path for the electricity to flow up one arm, through the very surprised person's chest, and down the (now deceased) person's other arm.

In addition to more safety, a bigger box would give me a chance to pile all kinds of cool dials and switches onto the front. I could have made such a box, but I don't really have the necessary woodworking tools. (Or skills, for that matter.) Fortunately, I found a plywood box which was absolutely perfect at a thrift store called "Habitat For Humanity," for only $2. It's about 17.5" x 12" x 20", with an open back. It's made of 3/4" plywood.

Step 4: Assemble the Parts

Time to go shopping! As I mentioned, I loved this step. In fact, this step and the previous one overlapped by quite a bit; my plans changed based on what I could find, and what I looked for changed as my plans changed. Here's what I had when I began the assembly:
  • The transformer (Input: 120v, Output: 15,000 volts, 60mA)
  • Cylindrical glass vase
  • Two 3' sections of stainless-steel coated rod, 3/16" diameter
  • Galvanized ventilation adapter, 8" to 6"
  • Glass dome from a ceiling fixture
  • Chrome trim ring from electronics salvage store
  • 7" flange ring from electronics salvage store
  • Lots of pipe fittings: Tees, elbows, joiners, flanges, and plastic lengths
  • Valve with red knob
  • 2 water supply hoses, braided steel
  • Sugar shaker (from 99 cent store)
  • Cheap rotating "disco" light (from Walgreens)
  • Power cord
  • 2 lengths of high-voltage wire (hard to find, but important!)
  • Can light fixture with trim ring
  • Switch box, switch, cover plate (from salvage store)
  • Plasma bulb (from novelty store)
  • 2 big ceramic insulators (from electronics salvage store)
  • a couple dozen water bottle caps, juice caps, jam jar caps, etc... (these will be the dials)
  • 2 handles, simple bent chrome tube ones
  • 2 handles, very strong galvanized ones
  • Hookup wire
  • A dozen or more bottle caps and lids
  • A few old knobs, dials, gauges, switches, meters, etc.
  • Calculator (from 99 cent store)
I ended up using a few other things, too (not pictured):
  • Foldable hand-truck (dolly)
  • Spray paints: textured rust, hammered metal, gloss black, primer
  • Weatherstripping

Step 5: Make Electrodes

We need a way to hold the electrodes securely, but still have the gap between them be adjustable. After imagining a bunch of different approaches, I saw these "threaded rod couplers" at the hardware store, and realized they'd be perfect. So I bought them, and a couple of bolts to act as retainers. Before bending the rods, however, I drew up my mental image of how it would work, just to flesh out the idea in my head, and get a feel for the dimensions I'd need.

The only thing I used for bending the rods was my bench vise and my hands. As you can see, I'm not exactly a pro at this... but they were plenty good enough.

Step 6: The First Test!

Once the electrodes were finished, I had everything I needed to try out the transformer for the first time!

For this test, I did a quick wiring of the power cord to the transformer's input power and ground terminals. Also, using the high-voltage wire, I connected the output insulators to the underside of my electrodes' insulators.

I adjusted the electrode gap to about 1", backed away, plugged the power cord in to my power-strip, and threw the power-strip's switch on. Nothing happened, but I did hear a soft buzz coming from the transformer, so I knew it was trying to do something. Shut off the power-strip, unplugged the power cord, and adjusted the gap (with one hand in my back pocket, a trick I learned from one of the guys at the electronics salvage store; it keeps you from ever creating a deadly circuit that goes through your torso). This time I tried a gap of 1/2", but still no spark. Next, I tried 1/4", and that seemed to be the magic number; I got a beautiful spark, which travelled up the electrodes perfectly! Almost as if I knew what I was doing!

A couple of slight adjustments later, and I was ready to film this test:

Step 7: Create the Supports

My design included a couple of uprights, one on either side, to keep the glass tube from tipping over. I decided to use plumbing parts, because they look so makeshift and fun. I decided to use metal joints, but plastic tubes for the straight sections to save on weight (also, I had a feeling an ability to flex would be advantageous later, and I was right).

This is a picture of one of them; the other side's looked basically the same.

Notice that I had already painted the pipes with a textured rusty paint, to look more like old metal.

Step 8: Attach the Uprights to the Top of the Cylinder

How do you drill into galvanized metal? This was new to me; here's what I found worked:
  1. Support the metal with a block of wood
  2. Use a centerpunch to mark the hole's location
  3. Use a small drill bit to make a pilot hole
  4. Use a larger drill bit to increase the size of the hole
  5. Use a spade bit to create the finished hole. Don't spin the drill too fast, and don't let it bind against the metal.
Then put a joiner piece into the hole, and lock it in place with a couple of 1/2" conduit nuts (these are in the electrical section of the hardware store).

Step 9: Add Spinning Light at Top

My device's top was based on a couple of parts I had found; yours will most likely be different. But in my case, all I had to do was place this cheap little spinning light thing on top of the inverted glass vase, and put the ceiling lamp glass on top of it, and it looked pretty much like I wanted it to.

Originally, I was going to wire this into the main power supply so I wouldn't have to change the batteries a couple of times on Halloween night, but I ended up not having time, so I just used its 3 original AA batteries. Turns out they lasted all night anyway!

Step 10: Add Dials and Gauges

Since I didn't have time to complete this step before the trick-or-treaters arrived, I almost left it out of this Instructable. But here it is, in case you're better at time management than I am.

This phase actually started a week or two before Halloween, when I asked my family to please NOT throw away any bottle caps, or jar lids, or things like that, and instead give them to me. They thought I was crazy... and now that Halloween's over, and they didn't see me use them, they're positive I am.

Here's how they would have all been arranged, if I had just started this project a day earlier. I like to see logical groupings, and contrasts between nearby shapes. I tried several arrangements before settling on this one.

Step 11: Create Finished Look of Box

The plasma bulb is in a standard ceiling "can" light fixture... just use a hole saw to drill a 4" hole in the front of the box, and install the fixture according to the directions that come with it.

At this point, I felt it looked too plain, so I:
  1. Masked off everything but 3/4" of each edge
  2. Painted these edges with a random combination of gold paint and rusty textured paint
  3. Grabbed some metal corners from an earlier project and screwed them into place
  4. Added galvanized metal handles, one to each side
Then, for ease of transportation:
  1. Attached a collapsible hand-truck to the back

Also in this view, notice that I've installed the switch box... It's wired up such that the plasma bulb is always on, but the Jacob's Ladder is controlled by the switch.

Step 12: Plug It in and Throw the Switch!

The last bits of set decoration:
  1. Added a reclining skeleton to receive electro-jolts via the braided steel tubing
  2. Added a motion-sensor skull, which would laugh and look at the Jacob's Ladder whenever I turned it on
  3. Added various other laboratory props, mostly glass and plastic stuff from the 99 cent store, on a metal cart
  4. Hooked it all up to a wireless remote controller, so I could turn it on and off from anywhere in the house
All of this was set up just inside a large window that the trick-or-treaters have to walk past to get to our front door. Whenever a trick-or-treater would come up the walkway, I'd press the button in my pocket and the sparks would begin... and when they were gone, I'd shut it off (didn't want it to get too hot).

It seemed to be a big hit, and I'm hoping to add more sinister props and devices to my "Mad Scientist" laboratory next year...

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