nikola tesla the man and his coil by matthew gebben, 35p
TRANSCRIPT
Nikola Tesla: The Man and His Coil By Matthew Gebben
Throughout history there have been many people who have made their mark by
contributing to humanity’s advancement. Many of these people have been largely
forgotten, while some went on to become legends. Scientists such as Newton and
Einstein, and inventors like Edison, rose to fame through their achievements. One man,
whose work has faded from the minds of many today, managed to accomplish more in
the creation of the modern world than most. Nikola Tesla, an inventor and scientist born
in the Victorian age, was a star in his time. He transformed the world, giving companies
the technology to send electricity to every corner of the world through the invention of
efficient alternating current systems. In order to understand this man and his creations
more, a thorough investigation into his life and inventions, especially his famous coil, is
needed.
Early Life
Born in 1856 in Smiljam, Croatia, Nikola Tesla would grow up in a rural
environment. With a father in the church, a mother who worked the fields, and four
siblings, Tesla had an eventful childhood. He began to invent at an early age, creating
such devices as paddle-less waterwheels and motors driven by insects.1 Much like his
mother, Tesla also showed signs of possessing great memory; his parents emphasized
improving memory and performing mental calculations. Tesla was also a voracious
reader, learning many skills in the process. Tesla’s childhood was not without tragedy,
however.
At the age of five, Tesla’s brother, Daniel, died in an accident which remains
shrouded in mystery. This event would affect Tesla for the rest of his life, and it is
possible that several of his unusual habits may have had their roots there.2 His obsessive
compulsive behavior included such things as counting his steps, calculating the volume
of what he ate, and favoring “numbers divisible by three.”3 Tesla would also develop
several phobias, including a fear of bacteria. Reflecting on his own childhood, Tesla
would later make several claims that did much to encourage a sort of cult following after
his death.
Tesla would claim to have seen visions of objects along with bright flashes of
light.4 Tesla’s claims, which also include superhuman hearing, among other things,
invited people to make bizarre theories on his nature. These theories ranged from Tesla
being a psychic to him being a Venusian who came to Earth.5 These strange conjectures
should in no way diminish Tesla’s true accomplishments, however. Tesla’s childhood
continued fairly normally, despite his supposed afflictions.
In his late teens, Tesla began to earnestly take interest in invention. Using his
excellent memory and visualization skills, Tesla would create and test ideas in his mind
before actually producing anything physical. Tesla’s mathematical ability also became
evident in school. Despite several bouts of illness, Tesla worked through his education
and enrolled in the Austrian Polytechnic School. His life there was quite different from
home.6
Tesla Emerging Genius and his Motor
Tesla was a very studious person. Studying much of the day, Tesla was
determined to make the most of his time at the school. His second year brought hardship,
however. The scholarship, which allowed him to live comfortably the year before had
been taken away, so Tesla had less than a year to stay. During this time, Tesla had plenty
of exposure to electrical equipment. One such experience is especially noteworthy.
“When one day there arrived from Paris a direct-current apparatus called a Gramme
Machine that could be used both as a motor and a dynamo, Tesla examined the machine
intently, feeling a strange excitement. It had a wire-wound armature with a commutator.
While operating, it sparked badly, and Tesla brashly suggested to Professor Poeschl that
the design might be improved by dispensing with the commutator and by switching to
alternating current.”7 (It should be noted that a commutator is a mechanical solution to
making direct current motors. Basically, in order for the motor to generate continuous
motion in one direction, the current had to be “mechanically switched to run first one way
and then the other.”8) Although the professor thought such a feat impossible, Tesla
would later go on to prove him wrong. Despite excelling at the school, Tesla’s financial
situation, not helped by his gambling, forced him to leave. Tesla would continue
studying on his own, with the problem of the alternating current motor staying in his
mind.
Tesla studied in Prague until he was twenty-four years old. During his studies, he
had to leave once when his father passed away in 1879. Then, in 1881, Tesla moved to
Budapest and secured a job at the new telegraph office. It was here that he would have
his revelation. While exercising with a friend, the design for the new motor was
suddenly realized. “Tesla’s long, waving arms froze in midair as if he had been seized
with a fit. Szigety, alarmed, tried to lead him to a bench, but Tesla would not sit until he
had found a stick. He then began to draw a diagram in the dust.”9 This would be the
revolutionary motor that would change the world.
The basic idea behind a motor is to send an electrical current through some wires
to create a magnetic field. Then the magnetized part, the rotor, will move to align itself,
giving the desired motion. A direct current (DC) motor must have to have something (the
commuatator) to physically change the magnetic field; otherwise, the rotor would simply
align itself and stop moving. Alternating current (AC) presents the challenge of a current
that is also changing back and forth in direction, making smooth, one-directional motion
difficult. By using more than one alternating current, Tesla realized he could create a
rotating magnetic field. This was done in an ingenious way. By using four coils in a
circle (for two currents), each ninety degrees from the other, and by attaching each
diametrically opposed pair to the same current (so that each pair operates on a different
current) the rotor would continuously move about as the magnetic fields from the coils
changed.10 This design is outlined in the following figure provided by
“http://www.allaboutcircuits.com/vol_2/chpt_13/7.html”.
Figure 1. Tesla’s Alternating Current Motor. (Note the four coils positioned at twelve, three, six, and nine o’ clock. These create the rotating magnetic field mentioned before.)
By expanding upon this concept, Tesla would have a great many designs.
Tesla’s First Professional Experiences
Although Tesla had the full design in his mind, he built no working model at first.
Instead, he continued to explore the concept and would think up many other useful
inventions in the following months. “He conceived of such practical alternating-current
motors as polyphase induction, split-phase induction, and polyphase synchronous, as well
as the whole polyphase and single-phase motor system for generating, transmitting, and
utilizing electrical current.”11 Nevertheless, Tesla had no means of building any of his
ideas; thus, he returned his attention to his work at the telegraph office. However, Tesla
was soon recommended to the Continental Edison Company in Paris. In 1882, Tesla
would find himself working for this company, and he was on his way as an inventor.
Tesla performed well at his new job, but frustration with his superiors caused him
to resign and emigrate to the United States. At the time, America was the center of the
electric revolution; Thomas Edison was busy spreading his direct current system and light
bulbs across the nation. Tesla wasted no time in going to work for the famous inventor.
Although Tesla was an excellent employee, the two men were fated to duel in one of the
greatest scientific and industrial competitions of the modern era. Once again, Tesla
would resign, but this time he would push forward on his own.
Tesla’s first attempt at business was a failure. The Tesla Electric Light Company
was created in the middle of a national financial crisis, so it came as no surprise when
Tesla was forced to move on. Working as a laborer, Tesla still managed to conceive of
new ideas. This inventiveness would help him greatly; soon Tesla attracted the attention
of “A.K. Brown, manager of the Western Union Telegraph Company.”12 Mr. Brown was
interested in Tesla’s dream of AC power, and he soon helped Tesla found the Tesla
Electric Company in 1887. Now Tesla would be able to show the world what he could
really do.
Tesla soon set to work filing patents for his new AC system. He was very
thorough about it, too. He filed patents for “the entire polyphase AC system. This was in
fact three complete systems for single-phase, two-phase, and three-phase alternating
currents. He experimented with other kinds too. And for each type he produced the
necessary dynamos, motors, transformers, and automatic controls.”13 These systems are
still in use today. The two-phase and three-phase systems simply have multiple
oscillating signals at the same time, as shown in the following figures.
Figure 2. The graph on the picture’s right shows a two-phase signal with a 90 degree phase difference. (http://en.wikipedia.org/wiki/Two_phase)
Figure 3. A three-phase signal with what appears to be a 120 degree phase difference. (http://en.wikipedia.org/wiki/Three_phase) Despite the innovations he had created, Tesla had yet to find a means to push AC as a
viable power source. Many were against AC because they had already invested in their
own DC systems. One company did have an interest in AC, however.
A Great Partnership and the Competition for a New Market
George Westinghouse’s company had also entered the electric power market, and
they had decided to go with AC. Although their operations expanded quickly enough,
Westinghouse needed to make his system more effective. It was at this time that Tesla
began to receive recognition. Tesla’s activity filing patents caught the attention of the
American Institute of Electrical Engineers, and he gave a well-received lecture to them
on May 16, 1888.14 Hearing of this, Westinghouse went to pay a visit to the inventor.
Tesla and Westinghouse got along with each other quite well. Tesla’s AC system
must have seriously impressed Westinghouse; he made Tesla an excellent business deal.
“…for his forty patents Tesla received about $60,000 from the Westinghouse firm, which
included $5,000 in cash and 150 shares of stock. Significantly, however, according to
Westinghouse historical records, he was to earn $2.50 per horsepower of electricity
sold.”15 Tesla would then go to work for Westinghouse, although he did not exactly get
along with the engineers; it took some effort to convince the engineers to use sixty cycles
per second (Hertz) as the frequency (60Hz was the frequency for which Tesla’s motor
had been designed). The other AC systems of the period were designed for 25, 30, or 50
Hz. With the nation’s economic crisis over, companies were looking to expand and the
“war of the currents” began in earnest.
Not wanting to lose business, Edison began to launch attacks on AC. Edison
proclaimed AC to be too dangerous, and set about distributing flyers highlighting this. In
addition, Edison collected animals from the neighborhood to electrocute with AC; rather
than say the animals were electrocuted, he used the phrase “Westinghoused.”16 Edison’s
campaign also managed to introduce the electric chair as a means of execution, using AC,
of course. Westinghouse launched a counter-campaign to educate the public, but, luckily
for them, Edison would soon have other matters to worry about. The Edison Electric
Company and the Thomson-Houston Company, a business under the control of J.P.
Morgan, merged in 1892 to form the General Electric Company. Unfortunately, Morgan
was about to make an attempt to take control of Westinghouse’s company.
Westinghouse’s determination to fight would have lasting consequences for Tesla.
Westinghouse was in a position of weakness against Morgan’s empire of banks,
railroads, and manufacturing firms. Morgan’s financial clout made the takeover seem
inevitable, but Westinghouse merged his company with several others to form the
Westinghouse Electric and Manufacturing Company. This was not enough, however;
some other way to stay afloat had to be devised. The deal Westinghouse made with Tesla
now came back to haunt him.
With the expansion of his business, Westinghouse had made an error. He now
owed massive royalties to Tesla due to their contract. Tesla could become an incredibly
wealthy man, but then Westinghouse could not compete with Morgan. Westinghouse had
to find a way out of paying the royalties, so he confronted Tesla with the problem. Tesla,
who wanted his system to succeed, had no problem with helping his friend. Tesla said to
Westinghouse, “You will save your company so that you can develop my inventions.
Here is your contract and here is my contract – I will tear both of them to pieces, and you
will no longer have any troubles from my royalties.”17 This act of generosity not only
saved Westinghouse, but it also doomed Tesla to later having financial problems of his
own. Whether or not Tesla considered the possible outcomes of renouncing his royalties
is unknown, as he was busy performing new experiments.
New Horizons
In his lectures, Tesla would demonstrate the products of his new research. He
often displayed his new lamps, many of which were glass containers filled with gas.
These were “the forerunners of today’s fluorescent lights.”18 Tesla had also begun to
discuss the possibility of sending power through the air or drawing it out of nowhere.
These ideas would prove to be some of the inventor’s more controversial thoughts.
However, Tesla also introduced his carbon-button lamp during these demonstrations.
The carbon-button lamp was a relatively simple device. It consisted of a partially
evacuated glass bulb with a small ball of “refractory material” in the center. The ball, or
button, was suspended there with the wire which would supply electricity. The whole
lamp, once sealed, would be supplied with high frequency electricity. The molecules of
gas left in the bulb would fly away from the button, but would be repelled back by the
glass walls. These molecules would bombard the button, heating it, and the process
would repeat. The bulb is said to have burned very brightly, and the button would often
get so hot that it would be destroyed. Tesla tested different materials for use as the
button, and carborundum (aluminum oxide) lasted the longest. Tesla stated in an address
to the American Institute of Electrical Engineers that this lamp was very efficient.19
Tesla had indeed begun work on many projects other than motors.
Tesla built many other notable inventions during this time. One of these, perhaps
his most famous, was the Tesla coil. This device is simply “an air-core transformer with
primary and secondary coils tuned to resonate – a step-up transformer which converts
relatively low-voltage high current to high-voltage low current at high frequencies.”20
Because this is such a famous invention, a full discussion of its details will be left until
Tesla’s life has been adequately covered. Although Tesla worked on many subjects
during the 1880s, the 1890s would prove to be just as productive, if not more so.
The 1890s began with Tesla putting everything aside and returning to Croatia.
His mother was dying, and Tesla was greatly affected. After her death, Tesla was sick
for quite some time. Nevertheless, Tesla resumed his scientific explorations upon
recovering. Tesla, who had taken an interest in using electromagnetic waves, gave a
series of demonstrations in 1893 not only detailing but also testing radio
communication.21 Tesla was making ground-breaking contributions to radio years before
the traditionally accepted inventor of radio, Marchese Guglielmo Marconi, demonstrated
his system. As later court cases would show, the title of inventor of radio would be hotly
contested for years to come. However, as these problems had not yet presented
themselves, Tesla had to turn his attention to other concerns.
Success and Disaster
A major success came for Westinghouse and Tesla at the 1893 Chicago World’s
Fair. The whole fair was supplied with power using Tesla’s AC system, and became a
windfall for Tesla and Westinghouse. Westinghouse was able to gain people’s
confidence by lighting up the fair and showing the safety of AC. Tesla was able to see
his system make an excellent impression on the visitors and had a chance to display his
other inventions. The fair was incredibly successful, and it heralded a new age of
technological progress. By this time, Tesla had become very famous, and the inventor
would soon enjoy the fruits of his success.
At the time, the Waldorf-Astoria Hotel was where all of the movers and shakers
would gather to socialize after work. Tesla, who enjoyed having as high class a life as
possible, often went there to mingle with the rich and famous. The great opportunity
these gatherings afforded was the chance to find financiers. Tesla was also able to
increase his fame through his encounters with others, especially the press. Tesla seemed
to have affected many people, as there are quite a few letters people wrote admiringly
describing the inventor. Despite keeping up a good social image, Tesla devoted himself
more to his work than to other people.
Tesla had been making progress with his radio experimentation, but this was to be
soon eclipsed. In late 1893, Tesla was informed by Westinghouse that the power of
Niagara Falls was to be harnessed to supply electricity, and it would use Tesla’s
alternating current system. Although Westinghouse was not totally in charge of the
project – General Motors would construct the power lines – Tesla’s AC system was
agreed upon by all involved.22 The Niagara project proved to be very successful, and
there is a large statue of Tesla at Niagara Falls to this very day. With the Niagara project
going smoothly, Tesla returned to his New York laboratory.
Hoping to make further progress towards his goal of wirelessly transmitting
energy, Tesla began to use higher and higher voltages. Using a modified coil he had
built, Tesla was able to get roughly one million volts.23 Occupied with testing new
inventions and contemplating his various theories, Tesla could not have been more
content. However, this happiness was not to last. In early 1895, Tesla’s laboratory
burned to the ground, destroying everything he had been working on. The fire’s source
was never really identified, but it was theorized that Tesla’s investigation into the
production of liquid oxygen may have been a factor.24 Now Tesla had to start over again.
A Fresh Start
Tesla’s fame helped him a great deal now; capital came in quickly, and the
inventor quickly set to work preparing a new laboratory. With the discovery of X-rays
announced, Tesla began his own investigation. At the time, the danger posed by
overexposure to the rays was unknown, and Tesla learned first-hand that safety measures
had to be taken. Both Tesla and an assistant were injured, although the assistant suffered
the most; he was standing very close to the emitting source for five minutes.25 This
accident was just one of many that Tesla would be lucky to survive. For instance, in
1896 Tesla received a shock of roughly 3.5 million volts at a low current.26 Tesla’s drive
to achieve higher and higher potentials would mean this would not be an isolated
incident.
Continuing his research, Tesla pushed his radio technology to new heights. Soon
he was able to transmit and receive over reasonably distances of a few miles. In 1898,
Tesla both received a patent for and tested a remote control boat.27 Not content with the
current technology, Tesla once again pursued the wireless transmission of power. His
announcements to the press would seem terribly premature today; Tesla’s statements
often made it sound like a great discovery had been made, when, in fact, nothing concrete
had been produced. This showmanship by Tesla not only increased his fame and helped
to acquire financial support, but would also later on work against him.
One excellent example of this exaggeration was the infamous earthquake
machine. Tesla had long theorized that if one sent a wave through some substance (by
hitting it, for example), energy could be slowly added by tapping it exactly when the
wave came back to the point of origin. This theory was blown out of proportion by Tesla
himself when he claimed to have used one of his mechanical oscillators to cause an
earthquake. Supposedly, he attached the oscillator to a pillar in his laboratory and the
vibrations went into the bedrock. According to Tesla, the vibrations were amplified each
time the wave returned to the oscillator, and eventually a small earthquake occurred.
There is no proof that this ever happen, but the myth persisted (no doubt Tesla helped: he
claimed the same principle could be used to shatter the Earth itself).28 This story was put
to the test on a Discovery Channel show called Mythbusters.29 In this program,
oscillators which performed the same function as Tesla’s design were used to try and get
a bar of steel to sway violently. The mechanical oscillators seemed to be too imprecise,
but an electromagnetic linear motor (it has a bar that moves straight back and forth) got a
reaction. Able to tune the frequency with precision in the hundredths of a hertz, the bar
of steel did indeed begin to vibrate violently at a certain frequency. When attached to a
unused bridge, not much happened until another specific frequency was reached. Then
vibrations could be felt throughout the structure, but nothing like Tesla claimed. Even if
Tesla was exaggerating, the theory manages to hold some weight. In between
increasingly incredible announcements, Tesla was still busy putting out noteworthy work.
Around the turn of the century, Tesla was still busy with his remote control
vehicles. Nevertheless, progress in other fields was made. Fascinating examples of this
can be found in patents 723,188 and 725,605. The patents actually were useful long after
Tesla’s death. “Their [Brattain, Bardeen, and Shockley] patents and the Tesla patents
were both directed at applications in the communications field, he [Leland Anderson]
notes. Both patents are combined to produced the physical embodiment of a solid-state
AND gate.”30 The AND gate is just one of the logic gates so important to the operation
of computers today. Even with successes such as these, Tesla’s desire to pursue radio
and the wireless transmission of electricity drove him to seek new grounds in which to
work.
Colorado Springs
In 1899, seeking higher voltages and more space, Tesla arrived in Colorado
Springs. Working outside of town, Tesla constructed a special laboratory where he could
carry out experiments at very high voltages. Luckily for Tesla, power would be free:
Leonard Curtis, the man who suggested Colorado Springs to the inventor, had invested in
the local power plant.31 The new lab had an antenna-like mast coming out the top, with a
metal ball topping it (something like the top of a giant Tesla coil). This building would
house the magnifying transmitter.
The magnifying transmitter seems to have been a large, modified Tesla coil.
What was special about this was the secondary coil. Tesla told Electrical Experimenter
that the secondary coil’s area was very large and its parts were “arranged in space along
ideal enveloping surfaces of very large radii of curvature, and at proper distances from
one another thereby insuring a small electric surface density everywhere so that no leak
can occur even if the conductors are bare.”32 In other words, Tesla avoided discharges
from the surface by increasing the area and thus decreasing the surface density of
electricity. Tesla said in the same article that either high voltage or current were possible,
but not both. He also stated that any frequency would work, and that the “tension,” or
voltage, only depended on “the curvature of the surfaces on which the charged elements
are situated are the area of the latter.”33 The whole system was designed to effectively
interact with the “globe” (Whether this refers to the Earth or the ball on the antenna is
difficult to determine considering the context). With this massive device, Tesla hoped to
push the envelope of projecting electrical power.
The magnifying transmitter appears to have been quite powerful. It seems that the
device created thunder from its long sparks and imparted an electrical charge to the
ground that could be felt easily. Expanding the facility’s capabilities, Tesla prepared to
make a high voltage, high current test. The test was impressive: very long sparks jumped
from the antenna’s top, and the thunder could be heard fifteen miles away.34 However,
the test was abruptly cut short by a power failure; the local power plant’s generator had
failed catastrophically. After helping to restore the generator, Tesla continued his
experiments in Colorado Springs. Indeed, his endeavors attracted a great deal of
attention, much to his annoyance.
Tesla, in order to be more secretive, had boarded up the window. This, in
addition to Tesla’s ill-advised decision to use a spring to make the main switch easier to
close, would lead to another of Tesla’s close calls. While working alone with a very
large coil, the spring mechanism failed, closing the circuit. Tesla was forced to dive to
the floor and crawl to the switch as electrical streamers filled the room. By the time he
opened the switch the building was burning. He was lucky to have been able to
extinguish the blaze. Even with events such as this, Tesla had reached new heights.35
In Colorado Springs, Tesla’s records show that 12 million volts and 1100 amperes
had been the highest voltage and current he reached. It also appears that ball lightning
may have been formed by some of the coils, and the radio receiver he built was quite
powerful for the time. However, Tesla’s dream of transmitting electrical power never got
too far. Although he believed he had made great progress, the idea would not get much
further. In 1900, Tesla moved to New York, and began work on what would result in his
greatest financial mistake.36
The Beginning of the End
Hoping to create a worldwide radio system, Tesla set about looking for capital.
He was not having much success until J. Pierpont Morgan agreed to fund the project. In
order to build a broadcasting station on the East Coast, Tesla bought an area of land on
Long Island. There he built a famous tower which became the symbol of the place Tesla
called Wardenclyffe. This 187 foot tower would act as a massive antenna. However, as
the equipment started to come in, Marconi, using one of Tesla’s patents and a station on
Cape Cod, sent a signal across the Atlantic Ocean; it appeared that Marconi was going to
profit by using technology he had no permission to use. Marconi’s growing fame made
Wardenclyffe’s increasing cost even more frustrating. Quickly running out of money,
Tesla again petitioned Morgan but found the financier uninterested. Despite Tesla’s
technical successes, Morgan lost interest and the money began to run out. By 1906,
Wardenclyffe’s fate was assured, and work soon stopped. The site fell into disrepair and
was finally sold in 1915.37 Tesla’s fortunes would never be the same again.
Tesla’s misfortune seemed to be growing rapidly. His fame made him many
enemies within the scientific community, and financiers were noticing a history of
unprofitable projects and wild claims. Along with this, the credit for who invented radio
increasingly appeared in jeopardy. Marconi, with his financial success, managed to get a
patent on his wireless system. For decades, Marconi maintained his position as the
inventor of radio, but not without controversy. Many lawsuits contested this claim,
including one by Tesla in 1915. Tesla’s enemies were quick to defend Marconi, but the
credit would not stay with them forever. In 1943, only months after Tesla’s death,
Marconi’s patent was revoked by the US Supreme Court. Although Tesla would finally
get the credit he deserved, he would not live to see it.38 Tesla would simply have to
persevere with what he could get.
Tesla had been affected by the misfortunes that plagued him. Some of Tesla’s
more unusual and unflattering traits became more prominent. His habit of showing off to
the press became more irresponsible. “Tesla would advance scientific claims recklessly,
discussing them with reporters fresh from the moment of inspiration with subjecting his
ideas either to experimental verification or even much reflection.”39 Needless to say, his
credibility suffered as a result. Tesla’s self-promoting may have been an attempt to
attract the attention of financiers, but its success is debatable. Tesla also picked up the
unusual habit of taking care of hurt pigeons, a habit that would be with him for the rest of
his life. Following attacks on his reputation or his inventions, Tesla also became more
aggressive in defending himself. Tesla’s creative genius had not dried up, however.
Fleeting Optimism
By 1906, Tesla had a new invention with which he hoped to achieve financial
success. This was the bladeless turbine, and, over the next few years, Tesla would
develop it into an effective machine. The idea was fairly simple: send a high pressure gas
between a set of disks. The material moving through would sort of stick to the surface of
the disk to get it to move. Ordinarily this would be an ineffective way to drive anything,
as most of the material would be too far from the surface, taking the path of least
resistance. Tesla realized that by spacing the disks closer together efficiency could be
increased.40 This turbine had the great advantage of simplicity. Thus Tesla set about
promoting the new invention and began to court possible investors and buyers.
During the first few years of the 1910s, Tesla had some successes with his
turbine. He had been able to interest several different European nations in licensing the
machine, including Belgium, from which Tesla received $10,000.41 Despite a few
successes, Tesla remained far short of the funds he needed and began to petition J.P.
Morgan, who had inherited his late father’s (J. Pierpont Morgan) business. This proved
to be not only unsuccessful, but harmful, as Morgan took the opportunity to bill Tesla for
the previous loan’s interest. Tesla continued to have bad luck, but in 1915 something
happened to offer hope for the future.
In 1915, the New York Times reported that the Nobel Prize in physics would be
shared by Tesla and Edison. Although surprised, Tesla speculated to reporters about
what discovery of his might have led to this honor. Soon, the news had spread across the
United States, and things were looking up for Tesla. However, the whole situation was
an illusion. The newspapers had been premature in their announcement of the winners,
and the prize would, in fact, not go to either Tesla or Edison. The recipients would be
William Henry Bragg and his son for discovering the structure of crystals.42 The
circumstances behind the rumor were never fully known, but the whole event must have
seemed cruel to Tesla. His predicament continued to worsen.
Tesla’s Final Years
Tesla’s turbine would also prove to be largely unsuccessful. The first period of
interest in the machine was ephemeral. Many were unwilling to invest in a new turbine
when the current ones worked fine, and Tesla’s turbine was, like most machines, having
problems. Tesla used German silver for the disks, but the operation speeds would prove
to be too much for this material. Indeed, suitable material for the disks would not be
available for years to come. Without enough money to do much of anything, Tesla
turned to the things he could do: thinking and speculation.
Although Tesla was still filing patents on occasion, the majority of work for
which he would be known was already in the past. His time was now spent
contemplating powered flight and designing lightning rods, among other things. Tesla’s
fame had, in one way, worked against him. Many thought the inventor was very wealthy,
so it came as a shock to many when Tesla’s relative poverty came to light in 1916. In
March of that year, Tesla was brought to court because he had not paid some of his taxes.
During this trial, Tesla’s real financial situation was totally revealed. While Tesla must
have been embarrassed by the whole situation, there was one positive outcome.
With the news of Tesla’s debts now common knowledge, many electrical
engineers felt that a great injustice had been done. Tesla had practically ushered in the
modern electrical age, and yet he was unrecognized for his achievements. With this in
mind, the American Institute of Electrical Engineers decided to give Tesla the Edison
Medal, their highest award. Initially, Tesla vehemently denied wanting anything to do
with the award that bore the name of one of his greatest rivals. One of the engineers who
pushed for Tesla to receive the prize, B. A. Behrend, set about trying to persuade the man
to accept the award. Although it took many visits, Tesla eventually agreed. Despite all
his earlier protests, Tesla attended the ceremony and gave a fairly long speech. Tesla
would treasure the Edison Medal for the rest of his life.
After receiving the Edison Medal, Tesla was a little more optimistic. He began
working to get out of debt and was trying hard to make successful business ventures. It
was an honest series of attempts, but nothing substantial came of it. Instead, Tesla was
finding himself more and more out of place with the world. Tesla, with his outdated
scientific beliefs in things such as the ether, could not come to agree with the work being
done in quantum mechanics and relativity. As science and technology advanced further,
Tesla’s work appeared to be slipping out of memory. Even the Westinghouse Company,
so much in debt to Tesla for his contributions, appeared not to remember or care: they
had turned down Tesla’s radio system while setting up their own.43 With the end of his
career seeming to be at hand, and with little recognition, it is no wonder that Tesla
became more eccentric.
As he aged, the pigeons which Tesla cared for became ever more important to
him. Kenneth M. Swezey, a friend Tesla had made in the 1920s, wrote that the elderly
scientist had dozens of pigeons in his care. Tesla could not even keep all of them in his
hotel room. Among all the birds, there was a white one to which Tesla had a deep
emotional attachment. When this pigeon died, Tesla was devastated. Tesla claimed he
could communicate with this bird, and that they had some sort of connection. He
supposedly said to his future biographer, “Yes, I loved that pigeon, I loved her as a man
loves a woman, and she loved me. When she was ill I knew, and understood; she came to
my room and I stayed beside her for days.”44 While this behavior in Tesla was certainly
unusual, it did show Tesla emotional depth. Even with the end of his life not far off,
Tesla proved to still have a knack for publicity.
The last decade of Tesla’s life was spent making flamboyant claims. Although
not everything he said was outlandish, many were quite unrealistic. Taking advantage of
his birthday parties to talk to the press, Tesla would announce things such as having
discovered a totally new, unlimited and free source of power. Of course, only vague
details were given, and nothing ever came of the matter. Indeed, much of what Tesla
claimed during this period would only fuel the theories of occultists later on, further
obscuring Tesla’s real achievements. An excellent example of this is Tesla’s so-called
death ray. The New York Times reported on the device on July 11, 1934 with the claim
that it was “powerful enough to destroy 10,000 planes 250 miles away.”45 Although
some rudimentary designs were drawn up, there is no evidence a real working device was
ever built. Nevertheless, after Tesla’s death, something of a conspiracy theory emerged.
It was claimed that the government had taken Tesla’s technical designs, and the concepts
had been taken up by both the US and the Soviet Union. Supposedly, Tesla’s death beam
theories influenced their work on directed energy weapons. Such stories are fantastic, but
they have made it sometimes difficult to distinguish myth from reality in Tesla’s life.
In the late 1930s, Tesla’s health began to falter. The elderly inventor was struck
by a taxi in 1937 and refused to go to a doctor. He eventually caught pneumonia and was
sick until the spring. Tesla never fully recovered, and his health wavered until 1943. On
the fourth of January of that year, Tesla was going to help an old working partner set up
an experiment, but had to leave early due to chest pains. Returning to his hotel room,
Tesla confined himself alone for several days. On the eighth, when a maid checked the
room, the inventor was found dead. Tesla had died the day before, probably of a
coronary thrombosis.46 The long and fascinating life of one of the modern world’s
greatest inventors had come to an end.
Nikola Tesla’s eighty-six years of life had transformed the world. Besides his AC
motors, Tesla had created a myriad of inventions. Tesla’s AC system made electrical
power practical and eventually brought electricity to every corner of the world. Tesla’s
fundamental radio patents paved the way for the mass media so ubiquitous today. Yet,
many of these great contributions are largely unrecognized today. However, one of
Tesla’s inventions had enjoyed popular recognition for various reasons. This invention is
the Tesla coil.
The Tesla Coil
The Tesla coil has been around for more than a century now, and its uses have
changed with time. What was once used for radio equipment and some medical
equipment (of an often unrealistic nature) is now used to generate lightning effects for
entertainment. To put it simply, a Tesla coil is a special transformer capable of putting
out a high-voltage, high-frequency signal. Tesla designed the device to do so by an
ingeniously simple method.
How it Works
The Tesla coil is not just one coil, but rather a set of four assembled into two
transformers. One of these transformers is simply a step-up transformer used to give a
high voltage from a relatively low-voltage source. This transformer, which operates at 60
Hz from the power line, often has an iron core to increase coupling. The second
transformer is a step-up, air-core transformer. This transformer has an air-core because it
needs to operate at radio frequencies, and the iron core of most transformers is a poor
choice for this. The common iron core is used to increase inductance, but at frequencies
above 1 kHz the electron spins in the iron cannot keep up with the applied magnetic field,
resulting in huge power losses.47 The air-core transformer does not suffer from the
massive power losses an iron core transformer would have at radio frequencies. Between
the two transformers, however, lie the “guts” of the Tesla coil, and the mechanism for
shifting to high frequencies.
A spark gap, a capacitor, and an inductor are wired up between the two
transformers. The set-up of this primary circuit can be found in the following figure,
courtesy of “http://www.richieburnett.co.uk/parts.html”.
Figure 4. The basic configuration of a Tesla coil.
This set-up means that the primary circuit, that being the spark gap, the capacitor,
and the inductor (primary coil), function as a separate circuit when the oscillations with
the secondary begin. Once the air in the spark gap ionizes and breaks down, the capacitor
discharges most of its charge into the newly created loop. Then the inductor resists the
current, eventually sending the current back to the capacitor. The cycle then repeats; all
this happens very quickly. In fact, the current, under perfect conditions, oscillates at the
resonant frequency, given by the following equation:
LCfo
π21
=
Eq. 1.48
Indeed, this equation governs the resonant frequency of both the primary and
secondary circuits. To help with this explanation of a Tesla coil, an example was
designed and constructed over a period of time. The procedure of its design, along with
its issues, will help create a better understanding of the functioning.
The Design
To begin, a resonant frequency was chosen. In this case, 700 kHz was selected
because a high frequency was wanted. From there, the wavelength (in feet) was
calculated using the classic equation λ=c/f (Eq. 2). Note that English units are often used
because many of the equations concerning Tesla coils are in those units (and are
approximations). Plugging in 9.84*108 ft/sec for c, and using the chosen frequency for f,
a wavelength λ is equal to 1405.7 ft. Since it is easier to begin on the secondary coil, this
is where the design begins to take shape. The secondary coil acts like a vertical antenna,
so rules applicable to antennas must be used. In this case, since the system is classed as a
medium-frequency antenna, a quarter wavelength antenna length is preferable; the
secondary resonates the best with a length of λ/4.49 Dividing the calculated wavelength
by four gives 351.4 ft, the length of wire needed for the secondary. A fine wire
(26AWG) was chosen for this to give a high number of turns. With its insulation, the
wire has a diameter of 0.032 inches. Then, a PVC pipe with an outer diameter of 2.355
inches was chosen as the base for the coil. Using these pieces of information, and the
formula Dπ+d (D is the pipe diameter, d is the wire diameter)50, the length of wire per
turn can be calculated (it is 7.4 inches). Dividing the length of wire by the length per turn
gives the number of turns, which happens to be 568.7 (which, multiplied by the diameter
of the wire gives the coil height, 18.2 inches). Of course, these numbers are just
approximations when the coil has been constructed, due to the somewhat crude methods
used. From here, equation 1 is the determining factor.
Since the secondary coil has an inductance and a capacitance of its own (plus the
capacitance of the toroid), the circuit on the secondary is nearly identical to the primary’s
circuit. There are also several approximate equations for determining these values. They
are as follows:
HANALs109
22
+=
Eq. 3. The Wheeler Formula. (The equation is accurate within 1% if the coil height H is greater than the pipe radius A. N is the number of turns, and all length units are in inches, while the value of the inductance, Ls, is in microhenries.51)
)(41
22so
sLf
Cπ
=
Eq. 4. The capacitance for a helical coil. (The capacitance Cs is in farads, the resonant frequency fo is in hertz, and the inductance Ls is in henries.52)
)(*)2781.1(4.1 CSODCSODCSCT −−= π
Eq. 5. The capacitance for a toroid. (The capacitance CT is in picofarads, CS is the cross-sectional diameter in inches, and OD is the total outside diameter in inches.53) In the case of the test coil, the toroid has an outside diameter of 11.1 inches and a
cross-sectional diameter of 3 inches. This results in a toroid capacitance of about
1.24*10-11 farads. When the known dimensions of the coil are put into the Wheeler
formula, the coil inductance is found to be nearly 0.00233 henries. Using this, the coil
capacitance turns out to be 2.22*10-11 farads. Note that these numbers suggest that the
actual resonant frequency of the coil will not be 700 kHz. Instead, using equation 1 and
adding the coil and toroid capacitances, the operating resonant frequency ends up being
561090 Hz. This is not a problem, provided that the primary circuit is designed with this
in mind.
The operating resonant frequency is used with a modified version of equation 4 to
find the dimensions of the primary coil. For the sake of convenience, a high-voltage
capacitor capable of handling radio-frequency circuits that was on hand was used. This
had a capacitance of roughly 0.005 μF and a maximum voltage of 15,000 VRMF. Putting
this into equation 4 with the capacitance and inductance switched, the needed inductance
is found to be about 16.1 μH. Then equation 3 can be used since both the wire and the
coil form had already been selected. Choosing a height of about 25 inches (to completely
encase the secondary), equation 3 yields a turn number of almost 37.4 turns. The chosen
wire was 18 AWG with heavy insulation, giving a total diameter of 0.016 inches. A 3.5
inch diameter PVC pipe was used as the primary coil form, so as to let the secondary sit
inside the primary. This arrangement would presumably provide the best arrangement, as
the setup allows for the greater interaction of the magnetic fields. The solenoid shape
creates a magnetic field that goes up in the center of the coil, following the overall
direction of the current.54 This way, the secondary is surrounded by the primary’s field,
and a current forms to oppose it according to Lenz’s law.55 Of course, since the
frequency will be high, the magnetic field is constantly switch direction, resulting in the
secondary coil’s alternating current. Checking the operating frequency, the primary
shares the secondary coil’s resonant frequency. The total primary coil wire length ends
up being 34.3 feet. The design is now done, but there are still several more details to
cover.
One convenient item to note is that the impedance for both the primary and the
secondary is the same. Both take the following form:
CjLjRZ T
ωω −+=
Eq. 6. General form of coil impedance.
22 )1(||C
LRZ Tω
ω −+=
Eq. 7. The general magnitude of coil impedance.56
Only the dimensions of the values differ between coil sides. On the secondary
coil, the resistance is supplied by the coil’s wire and by the separation of the terminal
from a ground; the inductance and capacitance are supplied by the coil and its terminal.
The primary side is more complex. Although the inductance simply comes from the coil,
and the capacitor gives the circuit most of the capacitance, the resistive impedance comes
from several sources. One of these is just the wire’s own resistance. The other two
sources are slightly more complicated. The spark gap does offer some resistance that
cannot be totally ignored. However, this resistance is not too great once the air between
the terminals has ionized. The most interesting cause of impedance in the primary circuit
comes from the secondary coil.
As previously stated, the primary coil’s magnetic field causes an opposing current
to form in the secondary coil. As might be expected, the secondary coil’s current then
creates its own magnetic field in the opposite direction. The result is a sort of reflected
impedance in the primary. This adds an extra term to equation 7 for the primary circuit.
Although the new term may appear simple, the truth is that there is some complexity.
The term takes this form:
s
p
ZMZ
2
fRe)(ω
=
Eq. 8. The reflected impedance.57 (Notice here that the operating resonant frequency is specifically for the primary, while the impedance in the denominator is for the secondary coil.) The fact that the coefficient of mutual inductance is here signifies that the
geometry of the coils in relation to one another greatly affects the reflected impedance. A
large mutual inductance results in a large impedance. As with many aspects of building a
Tesla coil, the equations for this mutual inductance are mostly empirical and are fairly
messy.58 This also holds true for the impedance of the secondary coil, as the calculation
of the resistance of the coil is made difficult by certain phenomenon at radio-frequencies,
such as the skin effect (which refers to the current being localized to the outer areas of the
wire due to “eddy currents”59). However, the reflected impedance would only reduce the
current and performance, rather than affect the functionality. The actual coil should be
noted before continuing, however.
Testing
With the design done, the actual setup should be detailed some more. Although
the following photographs are fuzzy, the design can be seen with some minor
explanation.
Figure 5. The Setup. (The tall gray tower on the left is the primary coil encasing the secondary coil. The long wires on both of its sides are connected to the ground, allowing for easy discharges.)
Figure 6. The Primary Components. (The black box on the top is the high-voltage transformer, and the red wire coming from its left terminal is connected to the gray-colored choke. From the choke, the wire goes to several resistors in series. Note that only one resistor is above the circuit board, and two are attached below. Then the wire goes to the large cylindrical capacitor and its path splits; in addition to going to the capacitor, the wire also goes to the spark gap in the upper right of the picture. Wires from the other terminal of the capacitor and spark gap are attached to the primary coil. Finally, the spark gap is also connected to the HV transformer.)
Figure 7. The Coil Tower and Toroid. This setup, crude as it may be, was constructed according to the calculated
designs. Once construction was complete, testing began. When the system was
connected to the power outlet several loud sparks were created. The spark gap ended up
creating the brightest and loudest spark. The sparks from the toroid were not so
impressive, but managed to cross roughly 7cm of air to get to the grounded copper wires
nevertheless. When the toroid was traded for a copper spike a small, continuous
discharge formed at the end, creating a small corona. It should be noted, however, that
removing the toroid should further reduce performance, and this did indeed seem to
occur. The machine worked great for a while, and was only used for a short period each
time. After several runs, however, a setback presented itself.
Error and Correction
After roughly 10 minutes of operation, a serious problem arose. When turned on,
the coil would not spark. The spark gap did not fire, either. This seems to have resulted
from the fact that the primary circuit is not totally disconnected from the power source.
Without proper measures being taken, some of the primary circuit’s radio-frequency
current leaks back into the high-voltage transformer. Since the transformer is designed
for lower currents and lower frequencies, the result is fairly detrimental. The iron core of
the transformer causes large power losses, and the energy goes into heat. In the case of
the test Tesla coil, the 12,000V transformer was broken by this RF current. In order to
protect against this, a choke, an iron-core inductor, was put between the primary and the
transformer. This way, any RF current would be countered before reaching the
transformer. In addition to this, the current in the system was reduced by adding power
resistors. This, combined with the use of a 10,000V transformer, resulted in somewhat
poorer performance, giving weaker streamers about 4cm long. The end result was that
the coil diagram changed a bit.
Fig. 8. The practical setup of a Tesla coil. (The power resistors and choke have been added next to the high-voltage transformer, while the primary coil’s impedance, natural and reflected, has been represented by an additional resistor in the primary circuit.)
However, aside from its rather lackluster output, the Tesla coil was designed and
constructed successfully. The sparks produced seemed to be quite powerful, and were
capable of penetrating roughly a centimeter of wood to reach the ground. It seems to be a
very effective means of attaining high voltages and frequencies.
The Tesla coil is a fairly complex system, and there are still many details that
could be covered. It seems as though much of the material on the subject is, however,
empirical in nature. The most useful equations are approximations, but, like many high-
voltage devices, the tolerances are high. The Tesla coil is an ingenious means of
generating high-voltage, high-frequency electricity. Its design serves as an example of
Nikola Tesla’s genius.
Bibliography
1. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Pages 26-27.
2. Abid, page 29. 3. Abid, pages 19 & 29. 4. “My Inventions.” Nikola Tesla. Electrical Experimenter, May, June, July,
October 1919, republished by Skolska Knjiga, Zagreb, Yugoslavia, 1977, pages 12-13.
5. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 112.
6. Abid, pages 32-39. 7. Abid, page 40. 8. “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and
Noble Publishing, Inc., New York, 1999. Page 21. 9. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York
City, 2001. Page 44. 10. “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and
Noble Publishing, Inc., New York, 1999. Page 21; “The Inventions, Researches and Writings of Nikola Tesla.” Thomas Commerford Martin. Barnes and Noble, Inc., New York, 1995. Pages 9-15.
11. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 45.
12. Abid, page 60. 13. Abid, page 61.
14. Abid, page 62. 15. Abid, page 63. 16. Abid, page 67. 17. “Prodigal Genius.” John J. O’Neill. Ives Washburn, Inc., New York, 1944.
Page 82. 18. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York
City, 2001. Page 78. 19. “The Inventions, Researches and Writings of Nikola Tesla.” Thomas
Commerford Martin. Barnes and Noble, Inc., New York, 1995. Pages 176-178; “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 81.
20. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 87.
21. Abid, page 96. 22. Abid, page 119. 23. Abid, page 121. 24. Abid, page 129. 25. Abid, page 138. 26. Abid, page 139. 27. Abid, pages 111 and 145; “The Fantastic Inventions of Nikola Tesla.” Nikola
Tesla and David Childress. Adventures Unlimited Press, Kempton, Illinois, 1993. Page 218.
28. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Pages 150-152; “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and Noble Publishing, Inc., New York, 1999. Pages 77-79.
29. “Mythbusters.” The Discovery Channel. Episode 23, Season 3. 30. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York
City, 2001. Page 169. 31. Abid, page 171. 32. “My Inventions.” Nikola Tesla. Electrical Experimenter, June 1919, pages 112-
176. 33. Abid, pages 112-176. 34. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York
City, 2001. Page 183. 35. Abid, page 185. 36. Abid, pages 188-191. 37. Abid, pages 193-220. 38. Abid, pages 221-230. 39. Abid, page 232. 40. “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and
Noble Publishing, Inc., New York, 1999. Page 111. 41. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York
City, 2001. Page 238. 42. Abid, pages 243-246. 43. Abid, page 276.
44. “Prodigal Genius.” John J. O’Neill. Ives Washburn, Inc., New York, 1944. Page 316.
45. “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and Noble Publishing, Inc., New York, 1999. Page 144.
46. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 324.
47. “The Radio Amateur’s Handbook.” The Headquarters Staff of the American Radio Relay League. The American Radio Relay League, Inc., Newington, Connecticut, 1972. Page 37.
48. “Principles of Electronic Instrumentation.” A. James Diefenderfer & Brian E. Holton. Thomson Learning, Inc., United States, 1994. Page 55.
49. “Radio Engineering Handbook.” Keith Henney. McGraw-Hill Book Company, Inc., New York, 1959. Section 20-21.
50. “The Ultimate Tesla Coil Design and Construction Guide.” Mitch Tilbury. McGraw-Hill Companies, Inc., United States, 2008. Page 17.
51. Abid, page 76. 52. Abid, page 78. 53. Abid, page 156. 54. “Electricity and Magnetism.” Edward M. Purcell. McGraw-Hil, Inc., United
States, 1985. Page 231. 55. Abid, page 267. 56. “Principles of Electronic Instrumentation.” A. James Diefenderfer & Brian E.
Holton. Thomson Learning, Inc., United States, 1994. Page 55. 57. “The Ultimate Tesla Coil Design and Construction Guide.” Mitch Tilbury.
McGraw-Hill Companies, Inc., United States, 2008. Page 30. 58. Abid, page 100. 59. Abid, page 92.