~Jacob's
Ladder (The
Climbing Arc) ~
Information on
how to build a Jacob's ladder, and my Jacob's ladders.
Disclaimer!
Jacob's Ladders involves high voltages and
high currents can be lethal, destructive, or both. I am not
responsible for any damage to yourself, your equipment, blown
parts, country-wide blackouts, planetary disruptions or the
death of other people. In other words, a Jacob's Ladder is
extremely dangerous so be careful when operating one. The
information here is for educational purposes - build one at your
own risk.
Safety.
Make sure that no one
can come in contact with this setup - particularly curious
onlookers. Separating the potential victims from any possible
contact with the high voltage is really the only foolproof way
of protecting against fools or the unaware - and you from a
lawsuit. People not familiar with high voltage phenomena (or
aware only through sci-fi movies) can be incredibly naive, and
this can result in death.
15,000 volts will jump approximately anywhere between 1/2 inch
to 1 inch in air, and this might increase with sharp points and edges. This distance
occasionally varies unpredictably with humidity. Don't forget
that 15,000 VAC is approximately 21,000+ V peak. Neon sign
transformers have current limited outputs - 30 mA is typical -
but that is still highly dangerous - lethal under the wrong
conditions. Higher currents are surely lethal.
You can build a small Jacob's Ladder using a high voltage
transformer of lower capacity using a TV flyback transformer.
While these would be less dangerous, there is little room for
carelessness when working with any type of high voltage device.
Even if there is no resistive path, the stray capacitance can
permit enough AC current to flow to give you a painful or even
lethal experience!
Electrical discharges in air are also a producer of ozone which
may be a health hazard in large amounts. Make sure the area is
well ventilated. Strong UV light is also emitted by the arcs.
Since your eyes are not sensitive to UV, they might be cooking
without you noticing it if you stare at the arcs for extended
periods of time. They also can produce significant Radio
Frequency Interference (RFI) and Electro-Magnetic Interference
(EMI) so the police may come calling if you run the thing for an
extended period of time... (probably not though). |
Introduction
What is a
Jacob's Ladder?
A Jacob's Ladder is the
type of high voltage "climbing arc" "V" shaped display seen in
many old Sci-Fi movies. Jacob's Ladder come in all shapes,
styles, and sizes. It involves basically the use of relatively
high voltages and currents.
How does it
work?
The simple explanation
is that an arc starts at the bottom, and due to the fact that
hot air rises, the arc tends to move up the diverging rods until
they are too far apart for the voltage/current provided by the
power source.
Now lets analyse it
totally. The term voltage refers to potential, or like
water pressure. Current basically refers to electrical
flow, or like the volume of water flowing through a pipe. A
dielectric is something that resists the flow of electricity
until a high enough voltage is created, sort of like fish
clogging a pipe until the water pressure builds enough to blast
the fish and rush through. Okay, Air is a dielectric, and when
two points build up enough voltage between them, a spark jumps
between them, like lightning. Air is a fairly tough dielectric,
and takes about 1 thousand volts to jump 1.1mm. The voltage
determines the distance the arc can first strike the other
electrode. The current on the other hand determines the distance
the arc can be drawn after it has connected the two electrodes.
In a Jacob's ladder, both current and voltages are usually quite
high, so at anything, do not touch the ladder when it is in
operation!
However, it is not just
the fact that 'hot air rises' that contributes to the effect.
While it is true that warm air pushes the arc up the ladder,
there is also the typical 'high leakage' or reactance curve of
the transformer contributing to the effect. The transformer will
happily arc across the bottom as long as Paschen's Law
will allow. Once this arc is struck the current in the arc will
actually increase to the transformer's preset limit. The heat is
also creating higher resistance. Normally the transformer would
try choke the voltage down as current increased. But just above
the arc exists a path that the transformer can easily maintain
and which in fact will lower its current.
I have
tried for both AC and DC currents and they both work. |
Build a Jacob's Ladder
Basic Components
- Power Supply
Jacob's ladders are relatively easy things
to construct. There are only two major parts to a basic Jacob's
Ladder: a high voltage power source and a pair of rods arranged
in a narrow V configuration on an insulated and fireproof
support. You will need at least 6kVAC at 20mA or higher.
However, the exact values are not at all critical. Lower
voltages work, but not reliably. A neon sign
transformer is the usual source for this power though an oil
burner ignition transformer will too, or you could build an inverter type power
supply.
-
Neon Sign Transformers (NST) can be
obtained used from sign shops or metal recycling companies.
The cost will be anywhere from free to $150 or more depending
on size and condition and whether the seller has a use or
other buyers for this sort of equipment. Typical ratings:
7,500 to 15,000VAC current limited to 20 to 30 mA. Larger ones
are available - up to 60 mA or even 120 mA. There are smaller
transformers from 2,000V to 6000V but they do not produce a
very impressive display. When getting a neon sign transformer,
those heavy iron-cored transformers perform better and are
more study than electronic transformers (which can't quite
handle much abuse).
 
-
Oil burner ignition transformers (OBIT) can be
removed from discarded oil burners, and can be obtained
cheaply from junkyards etc. However, you
will likely have to disassemble the disgustingly icky burner
assembly and properly dispose of the unwanted parts as part of
the deal.
Typical ratings: 5,000 to 10,000VAC, current limited to 10 to
25 mA.
  -
Other lower powered devices like automobile
ignition coils and television flybacks will work too. A small
jacob's ladder is just as fun. Ignition coils can provide
various voltages and currents depending on the power fed to
it. Flybacks generally provide quite high voltages but at low
currents. They provide an interesting display too. Laser power
supplies can be used as well.
There are some other
power supplies, which I
do no recommend you use.
-
Microwave Oven
Transformers (MOT) produce only about 1,500 to 2,500 VAC which
is too low. Several in series would be required but this is an
extremely dangerous and unwieldy arrangement. They are not
current limited like NSTs or OBITs, and can put out up to or
more than 2 Amps
on the high voltage side, and will blow your circuit breakers. They
are LETHAL and WILL kill instantly due to the extremely high
currents. Save yourself and your house circuit breaker from
popping like pop-corn and do not use MOTs. *I have done one to
save you the trouble from doing it :) *  
-
Utility Pole and
substation distribution transformers. Aside from requiring a
forklift of or a 10 ton crane to move it, it will probably
blow your circuit breakers unless some heavy-duty current
limiting is installed. These are rated from 10kW to 25kW and
are even more dangerous than your electric chair... however,
the do make quite a lovely display...
|
Construction
Construction
Take a pair of thin metal rods -
the steel wire from old metal coat hangers works quite well. You can
also use some thick steel or copper wire.
Straighten them out and mount them on an insulated non-flammable
support with a gap of about 1/2 inch at the bottom and 1 to 3 inches
at the top forming a narrow tall 'V'. This depends on your power
supply and you'll need some experimenting to get the optimum
positions. Mounting locations should not
be in the path of the rising arc. Connect the high tension output of
the transformer to the two rods using high voltage insulated wire
unless the routing is such that there is no chance of arcing where
you don't want it. Some adjustment of the spacing at the bottom (to
get the arc started) and at the top (to determine when the arc is
extinguished and how fast it rises) may be required (but do so only
with the power tuned off!). Depending on the voltage and power rating of
your high voltage source, these dimensions may vary considerably.
Spirals and other more creative configurations are also possible,
but are more difficult to construct.
A Jacob's Ladder works on the
principle that the ionized air in the arc is a lower resistance than
the air around it and heated air rises. The arc strikes at the point
of lowest breakdown voltage - the small gap at the bottom. The
heated plasma rises and even when it is an inch or more in width is
an easier path for the current to follow. Eventually, the gap
becomes too wide, the arc extinguishes and is reestablished at the
bottom. For best results, shield the whole thing from drafts but
don't use anything that can catch fire! It's possible to use a large
diameter clear acrylic or lexan tube to shield the whole thing.
Basically it should look like
this. That's about as simple as it can get. You can make your own
base etc, like what I did.
Gabriel Electrode to
assist arc striking
The gap between the electrodes at
the bottom of a Jacob's ladder can be extremely critical. Too wide
and the arc won't strike, and too narrow and it will just stay at
the bottom. If you cannot acquire a high enough voltage transformer,
the distance becomes even more critical. This electrode would assist
arc striking.
It's simply a third electrode placed between the strike gap at the
bottom of the "V". It is connected to either one of the main
electrodes via two 1M ohm high voltage resistors. When an arc should
occur, the following happens...
1. The voltage on the middle electrode floats to the potential of
the electrode it's connected to via the resistors.
2. It's easy for an arc to jump the short distance from the other
electrode to the middle one.
3. When an arc has struck and current is flowing, the voltage on the
middle electrode flies up due to the high resistance value.
The combination of high voltage at the middle electrode and the
ionized path makes the arc strike all the way across. It's simple,
but works perfectly. |
* My
Jacob's Ladders *
Introduction
Here are some of the jacob's
ladders I have made, ranging from small flyback driven ones to NST
driven one. |
Flyback Driven
This is my first Jacob's ladder.
It's extremely small and powered by a small Television flyback
transformer (using a 50W lighting transformer... Made simply with a small plastic box, and two bent
wires.
Visit my
High
voltage flyback page for more information. |
Ignition Coil
Driven
This is my second ladder, pieced
together in a hurry. (click for larger image)
Higher voltage, but relatively
lower current than NST. Check it out the ignition coil driver at my
ignition
coil page. |
Large Neon Sign Transformer Driven
The
mother of my Jacob's Ladders!
Standing
about 70cm tall, constructed with bolts, nuts, and acrylic... the
large Jacob's ladder.
It's powered by a 7.5kV 30mA Neon
Sign Transformer with a Gabriel's Electrode.
Above is an animated sequence
showing how it going up the ladder. The grey block is the NST. Took
about 1 hr to drill and construct the base. The base is a bit small
though, and it's a bit wobbly, but this ladder is totally
spectacular
and the sound is just amazing.
It's a sure show-stopper at
parties. Lets see what happens when I fix it up next time.. :)
Below are more pictures of the
construction and the ladder in action. Click the picture for more
details.
The base construction and
the electrode in action.
Although simple, it's extremely
effective and works like a charm. This ladder is obviously much more
high powered than my previous ladders, and leaves the the ladder blistering hot. Always
remember to let the rails cool before adjusting it. Make sure it
can't fall down during operation!
Adding different salts on the
rails changes the arc colour.
On the left, you can see the arc
striking from the electrode fist, before rising up in this
long exposure picture.
More pictures of the ladder
in action..
Video Clips
This would not be complete
without a video of the ladder in action. It's much more amazing in
reality.
Download the video:
ladderbig.wmv (571kb. Requires Windows Media Player 7 or
higher to view) |
Powerful Microwave Oven Transformer driven
The
...father(?) of my Jacob's Ladders!
Here is my MOT driven jacob's
ladder setup. (click picture to enlarge) Although it's not very
tall, it has a more distinct "V" shape. The top is around 9cm wide.
It's powered by a 5.5kg Microwave
oven transformer from a 1.1kW oven. When shorted (in jacob's ladder
use), it should draw about 2000W from the mains. I don't have a
suitable measuring device so I cannot measure the output. Output
voltage would be around 2kV but at extremely high current! (1A)
If you can remember my
explanation above, the voltage determines the distance the arc can
first strike the other electrode. The current on the other hand
determines the distance the arc can be drawn after it has connected
the two electrodes. 2kV is way too little for a ladder to start
consistently by itself, therefore, I have made a simple trigger rod,
basically, a piece of wire taped to a wooden rod.
Assuming 2000W draw, that works
out to be 2kV at 1 Ampere (1000mA)! which is Extremely lethal. This
high current allows the arc to be drawn very wide.
The base is made of clear acrylic
(surplus piece) and the electrodes are made of thick steel wire.
Stainless steel would be more ideal but it is hard to obtain. At
these power levels, electrode erosion becomes a real problem. (This
ladder is about 2000W, which is significantly higher power than my
neon sign transformer jacob's ladder, which is only 225W. That's
almost ten times more power!) However, the display is spectacular...
And more pictures of the
ladder...
The base construction if the
ladder in the first picture. Note the terrible electrode erosion in
the second picture.
And the ladder in action.
This is a frame caught from a
movie clip. The arc is VERY bright and HOT. The ladder gets
Extremely hot even after a short run of a few seconds, and the
bottom of the electrodes can get RED HOT after long runs. Eye
protection is a must.
Remember, this is an EXTREMELY
dangerous setup due to the high currents involved. (even though
voltage is fairly low, but then again, 2000V can jump an air gap).
Keep it well away from you when operating ladder like these and
always turn off the power and allow the ladder to cool for several
minutes before tuning or adjusting the electrode spacing.
Video Clips!
This would not be complete
without a video of the ladder in action. It's totally awesome in
reality!.
Download the video:
motladder.wmv (798kb. Requires Windows Media Player 7 or
higher to view) |
5th
June 2004, 24th
October 2003
Jacob's Ladder
Gao Guangyan
Warning.. High
Voltage!
|