Introduction: How to Build a Five-foot-tall Jacob's Ladder

Picture of How to Build a Five-foot-tall Jacob's Ladder
This classic climbing arc completes any mad scientist's dungeon. Don't touch the electrodes: they're at 12 kV!

Step 1: Obtain Neon Sign Transformer

Picture of Obtain Neon Sign Transformer

Get a neon sign transformer rated for 9 - 12 kV and 30 mA. Make sure it's an old style, heavy coil transformer and not solid-state. The solid-state transformers won't start the arc.

I got a Transco 12 kV 30 mA transformer on Ebay for $35. It didn't have a wall plug, so I wired one on.

Step 2: Build a Base

Picture of Build a Base

Build a base from the something nonconductive and nonflammable. I chose wood, which doesn?t quite meet the nonflammable criteria. Drill two holes approximately 0.5 inches apart and shove two dowels in the holes. Use thick wire to make electrical connections between the output of the transformer and the dowels. Attach the base to the transformer to make the whole thing stable.

Step 3: Mount Copper Pipes

Picture of Mount Copper Pipes

Mount two copper pipes on the dowels. Make the fit snug by putting the wire between the dowel and the pipe.

Connect the transformer output to the stiff wire.

Step 4: Set the Spacing

Picture of Set the Spacing

Set the spacing at the top of the copper pipes. I used a laser cut piece of acrylic. Something like drywall could also work. Eventually, the spark hung out under the acrylic long enough to ignite it. In later versions I put a gap between the two holes to allow the spark to pass through.

You have to experiment with the spacing; start around 2 inches and go as wide as you can.

Step 5: Build a Case

Picture of Build a Case

To make sure no one grabs the pipes, build a case around them.

I cut pieces of acrylic on a table saw and attached them to the base and a small frame at the top. There is a piece of reflective mylar on the back acrylic.

Step 6: Power Up and Take Pictures

Picture of Power Up and Take Pictures
Power up and check the spacing. Make sure to unplug before you adjust any gaps!

Use a long exposure to take pictures.


SHOE0007 (author)2016-08-20

About 25,000 pulses a second.

SHOE0007 (author)2016-08-20

Soon I will make the Jacob ladder and use its RFI to attempt to kill bacteria. I am very creative. It may take a few weeks to get here. You have to be extremely careful and prudent with high voltage especially anything past 10 ma. Mine is a 8 kV, 20 mA at 25 khzs.

This mean in one second it fires about 1.7 pulses every second so in 1 minute the transformer and the jacob ladder will relase approx 102 pulses.

Ora (author)2008-06-16

I was thinking about making one of these and having it horizontal instead of vertical. Would this work, or does it need to be vertical in order for the spark to travel along the length of the copper pipes?

ewilhelm (author)Ora2008-06-17

It needs to be vertical. The spark heats and ionizes the air, which reduces its resistance. This heated air tends to rise drawing the spark up. You can blow the spark around, but doing so in a consistent manner would be a challenge.

killerjackalope (author)ewilhelm2008-06-17

Maybe a setup using a computer fan, something quite gentle, it would have to reacht the length of the arc rods though, you could use the power supplies case fan as a source of vaguely warm moving air, if it was a little warmer than room temp it would lower the heat gradient needed to make the arcs move, I think, cold air might have a more pronounced effect for a very powerful and slow moving arc...

Ora (author)killerjackalope2008-06-17

Hmm, that might work. If I give it a try I'll be sure to let you know.

killerjackalope (author)Ora2008-06-18

It should work ok if you can get the right airflow...

This would be very interesting if done inside a vacuum

Werehatrack (author)Hightechk2014-11-12

In a vacuum, there's no air to ionize; the spark probably would not start at all, and would never move from the point of shortest path if it did. And the electrodes would have to be MUCH closer together in order to get a spark to jump the gap.

ajrojee (author)Werehatrack2016-05-27

I know your reponse is old but I feel compelled to chip in: You're quite wrong, I promise you. In a vacuum the spark can travel much farther. I have, in fact, tested the theory. I had a 10,000v transformer capable of approximately 1.5" spark. It was managing around 6" in a -25in.Hg vacuum.

freakshow freak (author)ewilhelm2010-08-02

Having air entering top and bottom seems to help the spark rise, making a kind of chimney i suppose.

Ora (author)ewilhelm2008-06-17

Okay, thank you very much.

hdc77494 (author)2016-04-20

saw a news story today where a kid died building one of these, but I don't see any safety comments anywhere. What, exactly, do you do to keep this device from killing the kid you're building it for?

AaronS173 (author)hdc774942016-04-20

Step 5: Build a case

To make sure no one grabs the pipes, build a case around them.

I cut pieces of acrylic on a table saw and attached them to the base and a small frame at the top. There is a piece of reflective mylar on the back acrylic.

Megavolt (author)2013-10-21

I bought a Franceformer brand transformer off of ebay for around $40 that I believe was 12kv 30ma (Got my build info from‎). It had the ceramic insulators on each end and the three threaded stud power connections on one side. I bought a three prong plug and a power strip (for the on off switch) along with 12 feet of solid copper wire (I forget what gauge, but it was about the thickness of a pencil) and some connections for connecting the copper/coat hanger electrodes to the transformer. The associate in the electrical section of Home Depot advised me on how the plug would wire up to the transformer. I wired it up and used two coat hangers to make electrodes just to make sure it would work, then I painstakingly straightened the copper wire and made two copper electrodes that were about 6ft tall. They were so tall, that when I turned on the ladder, they were attracted to each other and it messed with the climbing arc. I solved that problem by putting a notched piece of plastic at the very top of the electrodes to keep them steady. It was awesome! Even with the much smaller coat hanger electrodes. I have since lost the transformer and copper electrodes, but I will make another one eventually and I would like to build a nice box for the transformer and plexiglass enclosure for the electrodes so the kiddos can't touch the pretty arc. I like the idea of a steam-punk inspired ladder. I'll be lucky just to get a regular box and electrode enclosure built. I like that you used copper pipe for the electrodes. That takes the bending aspect out of the equation. I'll probably go with solid copper wire again though because it reminds me of the old school ladders from the horror/sci-fi movies.

sjones124 (author)Megavolt2015-10-08

Megavolt do you remember how you wired up your 110V supply. It sounds like I have a similar transformer, and I was planning to use a three wire supply, but wasn't sure what to do with the ground. I know better than to connect with the neutral, which only leads me to believe I should use the case for ground, but I'm not savvy with high voltage. Kinda funny for a guy who works in a nuclear power plant, huh?

Digimeat1337 (author)2015-06-23

Could I use a 1MV Ultra-High voltage pulse generator for this?

Like this:

DiederikvD (author)2015-03-29

Hi, what kind of cable did you use for connecting the Neon sign transformer to the Jacob's ladder? Is it possible (and harmless enough) to use normal electric wire (like wire from electric devices)?

toadboy65 (author)DiederikvD2015-04-14

I used regular wire, 14 gauge, I think.

toadboy65 (author)2015-04-05

I made this with my kids, but modified the design somewhat. I used solid copper rods, threaded at the bottom, and bent so that the bottom gap could be adjusted with the nuts and washers. We used a 15KV transformer, and needed a 9mm gap at the bottom for the spark to start.

nickademuss (author)2014-08-06

nice build, some have been made using rabbit ear style antennas, very good conductors and they are chrome plated copper. They even have mounts, but in this day and age it's hard to find a set that's not bent up or painted black.

JosephPriestley137 (author)2013-09-10

Hi Guys,
I wanted to throw a couple thoughts out to the Jacobs Ladder community. I built a "steam punk"- inspired unit a while back for a Halloween project for my sports medicine physician. Materials used were an antique stained wood box to contain all equipment including wiring, Xformer, resistors, polar toggle switches, batteries etc. & also to serve as a decorative stand. Only one electric power cord for NST is visible from back of stand along with toggle switches. A brass face plate surrounds knife switch w/ ambient lighting coming from behind this plate by installing low cost plastic fiber optic cables. The knife switch turns power on to NST through an isolated system. Large brass clock gears with hollow cylinder extensions on their center axis are used as bases for each electrode fitting perfectly, and a decorative "power gauge" using a 50uA meter taken from a cold war-era Civil Defense radiation survey meter w/ blue LED installed inside to light up face of meter from interior which turns on by flipping rear toggle switch. The meter reads in units up to 50 RADs of radiation rather than the standard 50uA meter face normally encountered with a polished bezel surrounding it. An old-fashioned non-solid state 12kV NST used for powering, peaking at 1.414(?) that voltage if I remember correctly and carrying 20mA current.
I have tried a few techniques & wanted to share the ideas with the community to see if they can build upon them. Electrodes have been interchanged occasionally for wavy designs. I find wide spread electrodes breaking into a maximum arc length as conditions allow most appealing. Drafts can be an issue, "blowing" on arc & keeping it from climbing. If in container that is hermetically sealed, different gas fills can be used, including gas mixtures of varying ratios, to change ion effects, maximum arc lengths and colors as well as type of plasma whether more broad or "streamer"- like. Also if possible for some, being able to evacuate hermetically sealed container around electrodes also allows, if strong enough (!) for different pressures to be utilized to further effects. AC vs. half rectified & fully rectified DC can give interesting results. Higher frequency AC also works very well & increases the arc's changing tone. Using different setups, Jacobs Ladder can also fairly easily be turned into singing arc-able to play polyphonic music from CD, MP3, or radio input.
Lastly, coating electrodes in various salts can create beautiful color effects & even increase brightness of plasma discharge. My favorite is to make a paste of boric acid (found at most drug stores) by mixing with water & applying by hand to electrodes. It does not need to be put on evenly or coat electrodes entirely. I find when the paste is wet the color & brightness are most spectacular giving a beautiful green arc-either because the moist paste allows the boron ions to be more freely released or possibly the breakdown of some water content into small amounts of hydrogen & oxygen increases UV output, pumping more energy into boron ions & increasing emit acne of green light. Potassium salts may be used for purple, lithium salts giving reds, sodium yellows, copper salts blue-greens and so on. Glassblowers in Germany have since the early 20th C & continue to build uranium glass-enclosed Jacobs Ladders prebuilt with glass stand, connecting of power supply to electrode outputs all that is needed. Again varying pressures and gases are occasionally utilized. With uranium glass, a yellow-green glass containing 2% uranium on average, the glass enclosure will fluoresce beautifully from UV radiation emiitted from plasma arc. I would love to see any others implement novel modifications & post their own results. Beautiful piece, Wilhelm! Thank you for posting a very original & quality setup for inspiration to others.

pkrouse (author)2012-05-22

I was experimenting with helium + jacob's ladders last year. I had an acrylic tube around my ladder's rods, capped at the top, glued to the bottom. I put a schraeder valve and a bleed tube in the bottom (opening in side the tube, naturally) and filled the thing up with helium. It made a *beautiful* violet arc. I ended up putting a rubber glove on the bleeder valve to handle gas expansion from the heat. I assume I had a leak somewhere, because the effect went away after a few days' time.

Also, the rods were brass, and tarnished. I thought the helium would prevent that ,but it didn't. Been meaning to repeat this with stainless steel rods and a better-constructed tube.

goober6 (author)2010-11-18

i can only find a 5 kv and 30ma transformer is that ok???

pdub77 (author)goober62012-02-14

This link should help you:

dwhole (author)2011-06-27

I just scored a 12kV and a 15kV transformer from a local neon sign company, for on $5 each! Haven't tested them yet, but the guy was cool, and said I can exchange them if they don't work. Halloween is gonna be sweet. Great instructable, one that I've always wanted to do.

dog digger (author)2011-01-01

I love it.
I love how it temporarily sends the camera out of focus

tinstructable (author)2010-11-30

You should try cooling the copper pipes with liquid nitrogen and then spreading them apart. Perhaps you could also get your hands on another NST and wire it in parallel with the current one to get twice the length of sparks!

dataa2 (author)2010-11-06

anyone have a good online source for suitable neon sign transformers for good prices other than the obvious ebay ?

brady911 (author)2010-05-30

is it just me or is it true that it will produce nitrogen gas or something of the sort. and it will fill the enclosement with the gas.

uGo (author)brady9112010-10-18

it makes O3 ( ozone) ;)

Jimmy Proton (author)2010-08-07

thats so cool, im making one. that is...after i get a transformer...

sarosh6 (author)2010-04-03

 Im using a similar NST rated 9kV and 30mA for my tesla coil. It was two brown terminals on the side (similar to yours but on the sides). One side has two such terminals and the other side has only one. Which one of these is input and which one is the output? Also, what wires have you used for connecting the mains to the transformer and what wires do I use with the output current? Thanks!

strmrnnr (author)2010-01-10

I just had a vision while reading this Eric.

I saw a similar ladder but with smaller, more flexible, tubing being used and the tubing was bent into curves and loops, some similar to a helical staircase. The sparks were traveling around the track of the tube in amazing patterns.

Idonet (author)2009-12-04

Can you tell anything about the circuitry you use to power that thing?

Idonet (author)2009-12-04

Wow! This looks really impressive.

hamjudo (author)2008-01-23

My electronic neon sign power supply works just fine in my Jacob's Ladder. It has safety features that aren't present in the old transformers, and it weighs a lot less. It is current limited, so that nothing bad happens when it is accidentally shorted. It has a builtin GFCI. (Note: a GFCI will only protect stupid people that touch one electrode and create a path to ground. It will not protect stupid people who touch both electrodes!) It has no trouble generating a spark. The power supply is rated at 35ma or 10,000 volts. Since it only draws 175watts, it must not be doing both at the same time. I used a marble floor tile as the base. I glued the transformer and a glass block to the base. I connected the wires to the glass block. It is putting quite a few watts into the arc. Most of that becomes heat, so the copper wires get really hot. The arc is even hotter. The GFCI means that this ladder is far more likely to start a fire, than to electrocute someone. It produces very little RF interference, so I assume there must be some filtering in there somewhere.

Prometheus (author)hamjudo2008-02-07

You have a tolerant "soft-coil" setup, but I should add that it would be advisable to increase the heatsinking capacity of any heatsinks (any aluminum blocks/flanges attached to components) by at least 200%, but do not tie them all together, as voltage potentials may exist between not allow an electrically-compatible connection between them unless one is implied in the circuit. Adding a fan would not be unwise.

The arc itself releases not just the imported power creating the spark, but also adds the atomic level to it. Any electrical arc can create temperatures over 9500C, no matter how minute it may seem, it is fire on a level still not entirely understood by the scientific community. A 100mW transformer can create more than 100W of heat output per for you on an atomically-driven perpetual-motion machine, or close to it.

The GFCI has only one purpose: To monitor a current difference between hot and neutral. When one exceeds the other by approx 100mA (depending on calibration), the unit trips, assuming what is called a "ground fault", and promptly disconnects both prongs of the plug through a double-pole contact (both sides removed at once) on what is called a "collapsible circuit" (fault = open with a manual close, in most cases), borrowed from bomb-making technology.

If you have a blown hair dryer, saving the cord and GFCI is smart, even in dry conditions. One day, one may save your life by pure accident, noticing you to be the "ground-fault", which is what they aspire to detect in the long run. The GFCI will immediately recognize a short (probably within 100ms) and trip, and may just prevent a fire as well. Any electrocution will likely be more a lesson learned than a trip to ER....Most Americans need this to ensure safety from themselves and their own ignorance.

All a GFCI needs is a disparity of current on one side or the other....and while it may not save you from a painful shock for stupidity, it may still save your life....Worth using as an additional precaution.

hamjudo (author)Prometheus2008-02-07

I wasn't very precise. The GFCI isn't on the input to the power supply, it is on the two 10kV output leads. I believe this is called a "secondary GFCI", because if the high voltage power supply were a simple transformer, the GFCI would be connected to the secondary winding of the transformer. The 110V portion of the circuit is electrically isolated from the 10kV portion except for a single ground connection, a high voltage current ground fault, even if it goes through a person, is unlikely to create a current imbalance in the power cord. You still want a 110V GFCI to protect against ground faults in the mains portion of the circuit. The neon sign power supply barely gets warm, it has more than adequate heat sinking. Neon sign power supplies have to work when installed in badly ventilated metal boxes as part of an exterior sign of a restaurant in the desert.

Prometheus (author)hamjudo2008-02-12

I might have been unclear as well, the GFCI won't see you from the other side of any isolation transformer, such as neon-sign transformers. A "ground-fault circuit interrupter" can only protect you from the mains current. At the least having one on the kit gives someone a quick and safe way to kill power (by hitting the "test" button), without having to fight a plug loose, but this should not be used as an on/off switch. Tripping the safety manually should be done only in emergency or the potential of one. A GFCI on the secondary side is something I haven't heard of, but it would work in the same way. If one does exist on the secondary side, it will definitely see a person as a ground fault because us bags of meat are far more conductive at 10kV that the current would well exceed 100mA.....but for a secondary-side unit, especially in this application, would trip on at least 5mA. I still prefer the old-school heavy-coil transformer as there is less to go wrong, and it has a purist aspect to it. Solid-state power supplies are prone to the EMF created by an arc, where a heavy-coil type inherently absorbs it. The only remaining RFI escapes directly into the air. "It produces very little RF interference, so I assume there must be some filtering in there somewhere." The filtering is not on the power supply, but rather on other things you expected to pick up the interference. Per FCC rules, it is trying to block out unnecessary interference while not creating any of it's own. I'd give the credit to your other electronics rather than to your kit, as you are using it in ways it wasn't designed for. (In any case, got a make/model for your neon power supply? I'd like to get my hands on one too)

_Manni (author)Prometheus2009-11-12

To be on the safe side, how powerful should my transformer be? Note that it is a school project and im taking precautions. lol i don't wna kill anyone.


ewilhelm (author)hamjudo2008-01-24

Awesome! Can you post a picture?

Zaphod Beeblebrox (author)2009-10-24

yep it is

puffyfluff (author)2008-09-01

Thanks. Wow, she really likes teddies. muah hahahahahaha! people will bow down to me! arcs will be my aid! muah hahahahahahahahahahahaha!

duct tape (author)puffyfluff2009-10-20

It is kind of annoying when half of a conversation is removed.

matt (author)2009-09-29
Heres mine:

bombmaker2 (author)2009-09-18

that looks alot like the one from the franklin institute

ewilhelm (author)bombmaker22009-09-18

I briefly worked at the Franklin Institute while in high school.

bombmaker2 (author)ewilhelm2009-09-19

is it modeled after the one in the electricity section?

rocketman221 (author)2009-09-18

Cool jacobs ladder but its not good to use wood for a base. I used a scrap of 4" pvc pipe on mine.

About This Instructable




Bio: Eric J. Wilhelm is the founder of Instructables. He has a Ph.D. from MIT in Mechanical Engineering. Eric believes in making technology accessible through ... More »
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