Intro: 15,000 Volt, Jacobs Ladder Display
A Jacob's Ladder is a high voltage device the will continuously produce an electric arc that rises upwards. They have been around probably since people started experimenting with electricity. Commonly seen in classic monster movies or mad scientist's laboratories. While they do give off some light, they serve no practical purpose other then to demonstrate the awesome power of electricity. I built this one to be a demonstration in an Electricity class I was teaching.
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In this Instructable we will build a Jacob's Ladder enclosed in a nice looking protective acrylic case that can be used relatively safely. Keep in mind that Jacob's Ladders are inherently dangerous.
- Contact with the exposed high-voltage conductors can be lethal.
- The electric arc can burn through wood and other materials and start fires.
- The arc can produce significant amounts of ultraviolet light which could be damaging to the retina of the observer.
- The arc will ionize the atmosphere, the resulting ozone can be damaging to the lungs and the mucous membranes.
Step 1: Materials
- 15,000v Neon sign transformer
- 4'x4'x3/4" MDF sheet
- 4'x31"x1/4" acrylic sheet
- 4 3"x6" ceramic tiles
- spray paint
- wood glue
- Weld-On 4 Acrylic Adhesive and applicator
- pocket screws or wood screws
- screws with finish washers
- 14 AWG stranded hookup wire
- 10 AWG solid core wire
- Inlet plug with fuse and switch
- 5v power supply
- 5v LED strip
- 5-12v 80mm case fan
- 80mm Fan Filter with Grill
- 80mm Fan Finger grills
- 1/2" x 8' grounding rod
- 22mm Illuminated 2 position On/Off selector switch (#XB5AK124M5)
- power cord
- assorted crimp on wire connectors
Step 2: Enclosure
Let's start by building the enclosure. These instructions assume you have a similar size transformer, if yours is a different size you may need to adjust the dimensions to accommodate it.
- First, with a table saw cut the 4'x4'x3/4" sheet of MDF down to 6 pieces. One piece 4'x14" and three pieces cut to 14"x7" (we'll call these shelves). With the scrap cut two 3" triangles.
- With a hole saw, drill two 2-1/2" holes at about 4" from either end of the 4'x14" piece and drill three evenly spaced 1" ventilation holes about 2" from the long edge of one of the shelves.
- Attach the three shelves to the 4'x14" piece with wood glue and either pocket holes and screws or wood screws from the rear. If using wood screws be sure to drill pilot holes so you don't split the MDF. One shelf should be attached at either end and the third at 8" from the bottom.
- Attach the two triangle braces between the bottom shelf and the back in the same manner as the shelves. These will help support the weight of the transformer. Let the glue set.
- Cut a hole for the power inlet near the bottom left corner of the enclosure as viewed from the rear. This is not pictured in these photos because the part was still being shipped but the placement can be viewed in later photos.
- Sand the enclosure.
- Paint the enclosure.
Step 3: Fan and Grills
The fan is used to keep fresh air moving into the enclosure giving the arch plenty of air to ionize. But the fan, which is variable speed, will only be running at its slowest speed from the 5v power supply. This is what we want because a high volume of airflow would interfere with the natural rising of the arc.
- Attach the fan with screws to the inside of the enclosure behind the bottom (intake) 2-1/2" hole. Be sure to orient the fan so when it is powered it will pull air into the enclosure. Attach a fan filter grill to the outside of the same hole to keep dust and debris from being sucked into the enclosure.
- Attach a fan filter grill to the inside and a finger grill to the outside of the top 2-1/2" (exhaust) hole. These will keep dust out and fingers away from the electrodes.
Step 4: Wire
Time to start the wiring and prepare the neon transformer.
- My transformer is an old used Allanson transformer that looked like it had seen better days. I cleaned it up and sanded the case to prepare it for paint. I masked off the insulators and terminals and painted it orange then added a "High Voltage" warning sticker.
- Start the wiring by mounting the 5v power supply in the upper left corner on the back of the transformer compartment as seen in the pictures.
- Affix the LED strip to the underside of the middle shelf with its self adhesive back. If your LED strip has a USB plug on it cut it off and strip the wires back exposing the red and black thin gauge wires.
- Cut the connector from the end of the fan wires. We will only need the red and black wire, if yours has a third wire it can be removed.
- Connect both red and black wires from the fan and LED strip to the 5v power supply as shown in the wiring diagram.
- Next, using 14 AWG stranded hookup wire and crimp on spade connectors, pre-wire the fused power inlet as shown in the wiring diagram and pictures. Install it in to the enclosure in the opening made previously.
- Connect the power inlet to the 5v power supply and the 2 position On/Off switch as shown. Leave some extra length on the wires to the On/Off switch so it can more easily be installed into the back of the acrylic case later. Don't yet mount the On/Off switch.
- Mount the neon transformer to the bottom shelf and connect its AC IN terminals,using crimp on ring connectors as shown.
For more information on wiring the AC power inlet see this great Instructable by jwbrooks0 https://www.instructables.com/id/Wire-Up-a-Fused-AC-Male-Power-Socket/
Step 5: Insulators and Electrodes
Now we need to make the electrodes and insulators.
- First cut the grounding rod in half. The grounding rod has tapered ends, the two tapered ends will be the bottom of the electrode and the cuts ends will be the top.
- Then, cut two lengths of 10 AWG solid core wire (about 2' each) and strip the end of each about 1".
- Solder one of the lengths of 10 AWG wire to each grounding rod about 1-2" from the bottom. I needed to use an Acetylene torch to heat the rods enough to accept the solder.
- Drill a small hole on either side of the shelf to run 10 AWG wires through the shelf as shown in the pictures.
- To create the insulators, first drill two mounting holes in each of the 4 ceramic tiles using a masonry bit. You will want to use a template or jig to make sure all the mounting holes line up since we will be using two tiles on either end and the screws need to be easily inserted through both. The hole size should also be slightly larger then the screws you use.
- Next drill two more holes, in only one tile, with a larger bit that will be the correct size to accommodate the beveled end (bottom) of the grounding rods. The distance between these holes will determine the spark gap. You will have to experiment to find the correct spark gap for your transformer. If they are too close the arc may not rise but too far apart and you may not get an arc. I went though a few tiles before I found the correct gap.
- Next repeat this step on another tile for the top of the electrodes using a larger bit since this end of the grounding rod isn't beveled. It should slide though this tile. The holes need to be further apart so that the electrodes form a "V" shape. Determining this distance again will require some experimentation. If the electrodes form too narrow of a "V" the arch will get "stuck" at the top but too wide and the arc won't rise very far.
- Mount the insulating tile (2 mounting holes) and the bottom tile (4 holes) on top of one another to the center of the shelf using rubber washers, flat washers and flat head screws.
- Repeat the last step for the top of the electrodes using the other two tiles and mount capturing the electrodes between the tiles. The electrode will need to be trimmed to length. Be sure not to cut them too short since they are only held in place by being captured by the holes in the tiles.
- Run the two 10 AWG electrode wires through the two small holes in the shelf and connect to the transformer.
REMEMBER, CONTACT WITH LIVE ELECTRODES CAN BE LETHAL! ALWAYS UNPLUG BEFORE WORKING WITH THE ELECTRODES OR TRANSFORMER!
Step 6: Acrylic
Time to build the acrylic case. If you aren't familiar with how to work with acrylic or how to glue it you may want to watch this video on the basics.
- The build the case, you will need to cut the 1/4" acrylic sheet into three pieces sized to the three sides of your enclosure. Don't forget to add an extra 1//4" to allow for the overlap in each corner.
- Glue the three pieces together using Weld-On 4 Acrylic Adhesive and applicator. I would recommend making a quick jig to hold the pieces while gluing.
- After the glue has set, use a hole saw to drill the 22mm hole for the on/off switch in the front of the case. To avoid cracking do not apply much pressure to the drill.
- Remove the wiring connector from the back of the on/off switch and insert the switch into the hole. Secure with the supplied nut. Plug the connector back in to the switch
- Place the case over the enclosure. Drill evenly spaced pilot holes around the edge of the case to secure to the enclosure with screws and matching finish washers.