The second version Tesla Coil 4-inch in diameter is driven by 4 microwave oven transformers (MOT’s) and puts out 4 foot sparks.
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Tesla Coil 4-Inch ver 2
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Category Archives: Tesla Coils
Introduction
A Tesla Coil is a high voltage device that makes big sparks. It was pioneered by Nikola Tesla over 100 years ago. This is an introduction to my many Tesla coils and their effects.
More technical explanation: In its simplest form it is an air cored transformer driven by discharging a high voltage capacitor (eg 10 kV) through a few of the primary turns. A resonance occurs with this capacitor and the few primary turns (eg 100 kHz). This induces current in the tall secondary with many turns (eg 1000). A high frequency resonance of the same frequency occurs between the inductance of the tall secondary coil and the capacitance of a rounded metal object (typically a donut shaped toroid). A very high voltage (eg 200 kV) results in electricity (streamers) directly into the air or sparks to nearby objects. Best results occur when the number of primary turns makes both resonances equal in frequency.
A Tesla coil such as the one above with sparks of 8 feet equates to perhaps 250,000 Volts. It is very hard to measure this voltage directly.
A simplified circuit diagram of one of my Tesla coils is shown below with various filter circuitry and safety spark gaps to prevent the very high voltages from wreaking havoc with the lower voltage side. It uses 4 microwave oven transformers (MOT’s) driven by a variac. These take 240 V AC mains and supply about 8 kV to the primary coil, capacitor and spark gap. This circuit is resonant at about 100 kHz and drives the secondary coil and toroid which are resonant at the same frequency.
Tesla Tree
A 63 second exposure shows a Tesla tree of sparks for Christmas . These come from a 8 foot metal rod which acts as a rotating breakout point that is progressively raised in a spiral so sparks extend from ground level up to a high of about 18 feet. Hoping my umbrella will protect me here.
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Longest Sparks
These are the longest sparks of 11 feet that I have had with this Tesla coil on domestic power. They only happen occasionally though. (something about the 3 longest sparks looks like a T. rex).
This is a run with everything maxed out. The spark gap was running at its optimum of 400 BPS and the series blower gap was on full. I had a total of 0.11 uF of tank capacitance. I tuned things by hand and with the tuner to 36 kHz. The variac was on full and no ballast. No idea what the current draw was. I imagine 30 A plus. I have a tape measure on the ground which was only really countable in the high res photos but was set at 11 feet. The secondary winding length is 52 inches which gives a ratio of spark to secondary length of 2.3 which is fair enough.
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Photo Date: September 9, 2007
Multilayer Tesla Coil
This is a multilayer Tesla Coil. It is a still uncompleted unusual Tesla project. It is a spark gap driven air cored resonant transformer, i.e. Tesla coil.
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Tesla in the Moonlight
Ain’t this just like “the cow jumps over the moon“? A simple shot of Tesla coil sparks framing the full moon in the background.
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Moonlight Google+ post: Aug 8, 2011
Photo Date: April 11, 2009
Briefcase Tesla Coil
Tesla coil in a briefcase. This is my latest easily portable mini coil which gives 2-3 inch sparks. These are great fun and are generally safe due to the low power.
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Tesla on a Car
Tesla on a Car, 2005
Now this was a long time ago. For a bit of silliness, I put the mini Tesla coil above on my car.
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My First Tesla Coil Discovery
My first TC was ‘discovered’ while running a spark spectroscopy project (above) in high school 40 years ago. This used about 10 kV from multivibrator excited dual ignition coils through 10 turns of an air cored radio coil to quench it. The other end of the 130 turn coil developed a corona visible in the dark spectroscopy room. It was a truly amazing sight.
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My First Tesla Coil
My first Tesla coil using a neon sign transformer with a ferrite cored secondary giving 2 inch sparks. I developed this idea with an old transformer from a dumpster which in retrospect was an old unpotted NST (neon sign transformer). I used a single static gap with a 12 inch ferrite cored coil of 11 primary and 100 turns secondary giving 2 inch sparks with 26 small ceramic capacitors with 2 strings of 13 x 10 nF at 2.5 kV each. It ran nicely for about 20 years! This photo is a mock up with most of the original parts.
I developed this from my first “Tesla coil” discovery while doing a spark spectroscopy project. Years after I made it I heard that Tesla had beaten me to that discovery by quite a few years! This photo is a mock up with most of the original parts.
It now has new life as a Jacob’s ladder.
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Photo Date: Jan 19, 2003