TESLA COIL DEMONSTRATION                                       HOME


I have been fascinated experimenting with high voltages for long time and it has been quite some since I had played with one of these...This past summer I decided to built one as class demo for CIRCUITS I.  This is perfect demo to show what an electrical resonance can do...Produced high voltage discharges are small lightning bolts essentially...

There was a lecture on the principle of operation of the Tesla coil and a demonstration right after that in the Circuits class on
Dec 4th, 2006 and the following week for freshmen Science of Nature Class on Dec 11th.

Here is the clips from the demos...note the screen on the back going nuts as the Tesla coil operates...Movie files are mp4. 





This demo is with a fluorescent light...As the end of the tube touches the discharge I feel a mild shock. Coil operates at 400 kHz which the nerve system cannot respond but it is pulsed at 100 Hz so there is 100 Hz and its harmonics exist in the discharge signal...which is clearly noticable!



These two below are recorded while a HeNe laser tube is sitting on top of the toroid. As you see the laser is almost about the lase...It is a fantastic scene...





WHAT IS A TESLA COIL?


Nicola Tesla, inventor of AC power generation and distribution among others, a genius of late 19th and 20th century.
One of his most influential and famous invention was the Tesla coil. Unlike his contemporary and rival inventor Edison,
he was a real scientist and the unit of magnetic field intensity is named after him. 1 Tesla = 10^ Gauss.

Tesla coil is basically a high frequency resonant transformer. With his original coils he was able to lit light bulbes miles away. This circuit is basically the first wireless transmitter, first RADIO! (called spark gap radio).

Although almost everybody thinks that Marconi invented the radio (he was actually was a business man with cash...hired some engineers to copy the experiments of others...). The real inventor of radio is Tesla as the history is getting corrected as even the US patent office reissued the key radio patents to Tesla right after he died.

Since over 100 years people are fascinated with the Tesla coil, it has even cult like followers in the world...Exhibitions in science fairs and museums are quite common. In the US there are even companies that their main line of business is  performing Tesla coil shows in the high schools and universities to attract technically minded students into engineering and science...

In this lecture, I will explained  the operation of Tesla coil in detail followed by the demo of our Tesla coil.
Later I will put technical explanations here too...

Below is an image of our Tesla coil in operation. This is a medium size coil, powered by 10 kV, 30 mA neon transformer...The high voltages produced can be anywhere between hundreds of thousands of volts to a million volt...though maximum here is more like 500 thousand volts I estimate...I will measure it some day...as one can imagine this is no piece of cake...

By clicking the picture you can access the video...Tesla coil is located in the Photonics Research Lab and
it is recorded there...If you cannot  access it try again later since the video file is on another server...



The toroid on the top of the tower (which is the secondary coil) acts like about 16 pF of a capacitor and it is a part of the series resonant circuit that is formed with the secondary coil...It gets charged to such high voltages and the electric fields are so large that the air surrounding the toroid gets ionized, air molecules are stripped from their electrons! As the electrons recombine with the atoms we see the intense blue light called corona discharge.
The spectrum of light contains significant amount of UV actually and it is not advisable to watch it with a naked eye long times...

Since there is about 20 % of Oxygen(O2) in the air...during the recombination of ions significant number of Ozone (O3) is produced and the Ozone is not safe to inhale in large quantities since it is a higly reactive gas. Also NOx compounds are also produced which are quite toxic, so the Tesla coil should not operate long times without adequate ventilation.


The blue lights at the bottom is from the multiple static spark gaps that is used to initiate the oscillations in the primary coil
as I will explain in the lecture.
 
Initially I am holding an old HeNe laser tube in my hand...Electric field is so large that the neon atoms are excited even though they are so far away from the high voltage discharges..as the atoms relax to ground state photons are produced which we see as  the characteristic neon light. Later in  the video you see that I am waving a fluoroescent light which lights up to the point where my hand is...Fluorescent light is filled with Mercury vapor...electric field again excites the Mercury vapor, most of the light that comes from Mercury is UV light but the phosphor coating on the tube converts the UV photons into visible white light...The glass between my hand and the ionized gas inside acts like a capacitor actually....Current continues thru my arm passes thru my body to the ground.  People think I have a bad hair day!

This is a demo of wireless power transfer in essence...
 
In general Tesla coil is a dangerous piece of equipment...At least the high voltage of Tesla coil do not produce any shock that can be felt since it operates at high enough frequency (400 kHz in our case) and the human nerve system cannot respond to frequencies that high
(and I don't know any other nerve system that can respond to it for that matter)...High voltage discharge from a Tesla coil may not kill a person...but can give some nasty burns...

HOWEVER, if there is a discharge between the secondary and primary (due to some physical error of placement of
cabling etc. or due to some random discharge) and at the same time if a person come into contact with one of the streamers, that might mean death in a microsecond! I don't think anybody would see the white tunnel and all in that case...

There are just too many Tesla coil related web sites as you could find easily with a simple search...Almost all of them -except  a few knowledgeable people- have a gross mistake in their Tesla coil setups. This mistake exists even in some Scientific publications...  They simple connect the grounds of primary and secondary of the transformer. This is extremely dangerous. The secondary ground must be separate than the primary as it must be a dedicated RF ground. It is not advisable to connect that to powerline ground either.  People might say well I did and it worked...Lightly speaking,  this is no different than well I am not using my seat belt and nothing happened so far...it takes only one accident...

Best is to use a dedicated ground installation of course...

In my case I use a piece of metal about 1m X 2m  on the floor as the RF ground and it works just fine....



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