My latest toy-A medium size Tesla Coil
Taking over two
years to build, I finally managed to finish this monster. You
might ask, what do TESLA coils do? The short answer is: They make big sparks! At 243
Kilohertz no less. This
particular one is capable of 30" sparks when running at full
power. The one in the picture, close to my head, is
about 20" long. The blue-violet discharges are very entertaining
and
you might say even spooky. Most of what you see is corona
discharges. The power companies hate them because they waste
energy.The concept was developed by Nikola Tesla the famous inventor who lived till 1943. It was his belief that power could be transmitted through the ether by contraptions such as this. He wanted to be able to send power to distant locations and not have to string up wires. These were the days when electricity for consumers was still in its infancy. Although small amounts of power can be transmitted this way, it would never approach an engineering break even. The basic design has changed little since his work of the late 1800's. It relies on two resonant circuits and the "Q" involved in each to boost the voltage to very high levels. It's a great educational tool for students of electrical engineering as the calculations are better understood now than years ago when it was more of an art. When you wish to step up the voltage most people think of transformers. This doesn't work so well as you increase the frequency. You reach a point where the combination of a transformer and tuned circuits work best. EE students learn that high "Q" circuits can boost voltage and impedance considerably if care is maintained.
Mr. Tesla was very instrumental in proposing AC or Alternating Current as a means of transporting power. His most notable invention was the AC motor and had over 700 patents. At the time, certain competitors were all behind DC transmission which turned out not to be the way to go. The U.S. Supreme Court finally credited him with the invention of radio which everyone thinks belongs to Marconi. Equipment from Tesla's lab was used for the first radio transmissions by Marconi. It was only after his death that he became recognized for his great vision even though some of his ideas didn't work. He died relatively poor and many call him "the most forgotten inventor of technology". More on Mr. Tesla can be found at: http://www.pbs.org/tesla/ll/index.html. Great reading if you're interested in Radio and early Electrical Engineering. At least three dozen books have been written about him and I'm sure you'll find them most interesting reading. Overall, this was a man that deserved much more credit. Did you know that he built the first Robot? He built the first remotely controlled vehicle? He held the patent on the Hypoid gear found in cars today?
My Coil Specifications:
The coil is of conventional design using double resonant circuits driven by a 9,000 volt neon sign transformer. Closing (firing) of the primary winding is by a double "spark gap" with pure tungsten electrodes. It's entirely home built with most of the critical parts obtained on e-bay. Cost to build: $150| Maximum Secondary Voltage at full power | 400,000 volts |
| Theoretical maximum spark length |
39 inches |
| Resonant Frequency |
243 khz |
| KVA of primary |
0.54 |
| Primary drive voltage |
9,000 volts |
| Primary charging current |
0.060 amps |
| Primary storage capacitor |
0.03uf @ 35KV |
| Primary spark gap spacing, 2 each |
0.193 inches combined |
| Height of Secondary |
20" |
| Secondary turns |
1176 |
| L/C primary |
500::1 |
| L/C secondary |
1,100,000,000::1 |
| Coupling between coils, K |
0.15, Considered light |
| Secondary measured operating "Q" |
60 |
Hazards:
It goes without saying that building a device of this sort doesn't come without some serious risks to your health if not careful. The voltages and currents in the primary circuit are very lethal. A current passing through your heart of about 0.02 amps is usually fatal. In most of our day to day lives, the voltage is not high enough to force that much current. Here, your dealing with 9,000 volts pushing more electrons through the body so the chance of reaching serious currents is almost guaranteed! Not good odds. With the primary driver running at 60 hertz, these high currents and voltages become a serious safety issue. Never attempt to operate a device of this type unless you understand the risks and how to manage them.
But what about the
400,000 volts that the coil can generate in the
secondary? Suprizingly, not near as much of a problem because of
"skin
effect" and much lower currents involved. In electrical
engineering we learn that high frequency
signals only travel on the surface of conductors. At 243 khz,
only about 5 mils of depth is involved. Our internal organs are
not exposed to these currents. Hence, working with the
secondary is much less hazardous. As a young man, I built a lower
powered coil and would let it arc to my hand, often. It would
only
give a tingle and maybe a mild burn. Since my heart has been
working some 55 years since then, ie, has aged a little and
wearing out, I'm not going to
pull
that trick again. Most Tesla Coilers now advise
against direct contact. The photo on the right was taken in 1988
at the International Tesla Symposium. These stunts are common for
the movie industry.Another hazard, even when the coil is turned off, is the primary storage capacitor. It can be charged to 12,700 volts and, like all capacitors, can retain that charge if not properly bled off. The capacitor is of very high quality and has little leakage. Safety circuits are included in the design but if they were to fail you could be "done in" even when the coil was unplugged. Standard safety proceedures must be followed when adjusting or working on the device to ensure no energy remains in the capacitor. Again, don't work with these devices unless you completely understand how to remove the risk. Two people have died working with Tesla Coils.
One more consideration is the generation of Ozone. Large amounts are created in the vicinity of big electrical discharges. The Ozone molecule, O3 is both a good guy and bad. High in the atmosphere, its desireable because it filters short wave UV rays from reaching the surface and helps prevent skin cancer. When Ozone is released near the surface, it can create an allergic reaction in some people. This often happens in smoggy areas such as Los Angeles because its a byproduct of pollution. It's also very corrosive. More on Ozone.
The primary spark gaps generate high levels of short wave UV radiation but this can be easily blocked by filters.
Since large amounts of RF energy are created, people with pacemakers should not be in the vicinity of an operating tesla coil. Because of the RF, it should only be operated in a grounded metal building such as my shop. This shielding helps prevent the operator from becoming a high powered illegal transmitter.
The largest Tesla Coil ever built still seems to be by Nikola Tesla himself. He demonstarted 60+ foot long arc's. The Tesla Coil was inspiration for the "particle accelerator" which is in common use today in nuclear physics. The Tesla coil is sometimes confused with the Van De Graff generator which is a DC device with low duty cycle.
Picture at right shows both breakdown sparks and corona
discharges. In a darkened room, corona can be seen extending for
several feet.An ion propulsion motor has been added to the experiments (photo not available) which involves spinning a disc by throwing off ionized gas molecules. Looks allot like a rotating fireworks display. Ion propulsion is an important concept for long distance space travel and is now being used in some of our interplanetary explorations.
Photo
at left shows a
neon lamp that is taped to an insulated post. It's just
floating.... no wires connected to it. The RF energy is
lighting the bulb brightly by
ionizing the gas inside. This was Mr. Tesla's inspiration
for generation of lighting w/o wires. He felt that you could
illuminate an entire city without having to string wires. This
type experiment also led to the discovery of the fluoresent lamp
which he's been credited. Various gases glow different colors
when excited. It takes quantum mechanics to explain how this
works which ultimately led to the discovery of the laser. Did you
know that the gas content of a bulb can be determined by just observing
the "line spectra" when it's ionized? The invention of the
spectragraph was the result of this observation along with quantum
mechanics. By use of this tool, Helium was discovered on the
sun before it was ever found here on earth. Science has provided
some amazing tools to work with.Can I see it in operation?
The motivation for building this
device was to encourage young people in the sciences. A number of
interesting experiments are available. I demonstrate this coil by
pre-arrangement for those interested. Certain experiments and
discussions would be
shown:- Lighting of light bulbs with no wires attached, transmission of
energy through the air
- Demo of my Ion propulsion motor. An application of
Ion propulsion. Idea is now being used in space
vehicles. More info at: FAQ
- Corona discharges, why and what they mean for power companies?
- Emission line ID, use of Spectrograph
- Review radiographs of others X-ray work
using home built equipment. X-Ray generation requires careful
shielding
and will not be
done with spectators present. It requires a HV source of which
a
Tesla Coil is an example. Man made generation of
X-rays involves accelerating electrons to an excess
of 25,000 volts in a vacuum and hitting certain heavy metal
targets. The higher the voltage, the more penetrating the
X-rays. Mr. Tesla was involved in this activity for a period
of time but avoided the health problems some experimenters had.
Did you know that some early color TV's had a slight
X-ray
generation problem? Did you know that X-rays can actually be seen
by the "dark adapted" unaided eye? Caution:
Don't ever try this!
- The role of the TESLA COIL in science history......... Its
contribution
to many other inventions and concepts such as high energy physics.
- Demonstation of Radio in Tesla's time......... using his
tools. The "spark gap" as an important device in generating RF.
- Review of Tesla's key patents. Discuss his battles with Thomas
Edison and the dirty tricks that were used against him. The real
story behind the
invention of Radio. The role of politics and "big bucks"
Did Tesla deserve the credit, not
Marconi?
- Having fun just viewing big sparks! Stimulate the thinking as to what other experiments could be performed?
- As time allows, discuss small lab nuclear fusion experiments, ie
"The Fusor". See below.
Where can I learn more?
Many many
books have been written about Tesla and his inventions. The
local library has several plus a new one seems to hit the
market every couple of years. You can find considerable material
on the Internet. Specific to the construction of Tesla Coils:
OK, what about the Fusor?
As you talk about Tesla coils, the conversation often migrates to nuclear fusion since the methods used involve high energy stimulus and compression in some form. In recent years their have been people claim that they have generated fusion reactions in the small laboratory. Cold Fusion in 2000 was mostly debunked but their is still limited evidence that excess energy was present in these reactions.
Another following supports the "Fusor" in which Philo Farnsworth
held a patent on
a plasma device that is reputed to produce "Fusion" by Inertial
Electrostatic Confinement", or IEC. Mr Farnsworth was the
inventor of Television and not disimular in nature to N. Tesla. Both
were somewhat
eccentric. Recent developments have shown that this concept has merit
for generating neutrons. In fact, at least one company now
markets a bench top neutron source using this device. You can
followup with more detail at: http://www.fusor.net
or a google search on "fusor". Generating excess energy still
seems to be something in the future.
The tesla coil is a poor choice for fusor experiments because its AC and doesn't produce enough current to be effective. An old X-Ray power supply is a much better choice.
In researching government documents, I found little mention of IEC. Could it turn out that a future N. Tesla or P. Farnsworth makes a discovery that debunks the billions spent by the governments of the world? Or, is this another "cold fusion" story? Makes for great reading for the young scientist............
Revised: 09/07/07