Should I build a Tesla coil for a Science Fair?
I don't recommend building a Tesla coil for a science fair for the following reasons:
Tesla coils (even small ones) are inherently dangerous. The primary circuit can contain hundreds of amps, which is certainly more than enough to be lethal. The primary capacitor can hold a lethal charge for quite a while, even after turning off the Tesla coil. The power supply will need to output a dangerously high voltage (at least 5000 volts, otherwise the spark gaps may not operate properly). The spark gaps produce loud noise and UV radiation. The high voltages will create some ozone and various nitrogenous compounds which can be damaging to the mucous membranes and can cause headaches. Tesla coils will emit a fairly large amount of RF noise, which generally isn't a problem but does have the potential to interfere with cell phones, pacemakers, radar, radio, etc. They can send voltage spikes back into the building wiring and potentially destroy anything that's plugged in. You'll have to restrict access to the area around the Tesla coil and constantly watch it - which is often impractical. While it's possible to mitigate some of these risks, a Tesla coil can never be made completely safe, and making it as safe as possible will make an already difficult project even more difficult.
Proper grounding can be difficult. A ground rod is the best solution, but pounding one in and running a line to it may not be possible.
Tesla coils tend to require a lot of adjustments and they often break down. Operating one safely, and keeping it running will require a fairly high degree of electronics knowledge and experience.
When all the potential safety issues, legal issues and practical issues are considered, it becomes clear that a science fair is not a good venue for a Tesla coil.
A solid state Tesla coil may be a possible alternative, but they share most of the same issues with classic Tesla coils. I recommend considering a Jacob's ladder. However, a Jacob's ladder still poses many safety issues.
What are some methods to improve efficiency and increase arc length?
Replacing a static spark gap with a rotary spark gap can increase arc length around 20%. Use a variac to increase NST supply voltage to 140V / 240V. Move the primary coil closer to the secondary coil (unless you see racing arcs on the secondary coil). Increase the size of the top load.
How much will my electrical bill increase after running my Tesla coil?
An average sized Tesla coil that generates 2' to 4' arcs typically operates on about 1000 watts. Electricity typically costs about $0.10 / kWh (kilowatt hour). Therefore to operate a typical Tesla coil for 1 hour will cost about $0.10 (however, it's very rare that a Tesla coil will be operated continuously for an hour).
If I switch from a 9kV NST to a 15kV NST will I have to rebuild the entire Tesla coil?
No. You'll need to adjust the MMC capacitance, reset the spark gaps and re-tune the coil. You can also increase the size of the top load and adjust the PFC cap, but you don't have to. All the other parts should work fine.
Does it matter if the primary and secondary coils are wound in the same direction?
No. the direction of winding will affect the phase in the primary and secondary, but it won't effect the operation of the Tesla coil. Try flipping your primary coil upside down and see for yourself.
Why build a Tesla coil?
Building Tesla coils is a great way to learn about electricity, electrical components, assembling / wiring components and safety. It's also a good opportunity to work with friends and family in a team effort. And creating lightning is totally cool! Although, I've had limited success impressing chicks.
How much does it cost to build a Tesla coil?
Cost will depend on many factors, mostly how much you can salvage. Used NSTs are often much cheaper, sometimes even free. MMC caps, magnet wire, good PVC and dryer duct are all difficult to salvage and will probably have to be bought new. A small coil might be built for under $100. A large Tesla coil with "nice" parts can cost several hundred dollars.
Where can I get the parts for a Tesla coil?
Many of the parts can be found at the local home improvement store (Home Depot, Lowe's) or at salvage / recycling centers, or on the Internet. Check out Alan's store at Tesla Stuff. He has a nice selection of Tesla coil components including "hard to find" and "one of a kind" items.
Can I harvest free energy or power an "off the grid" electrical system with a Tesla coil?
Many people have realized our fiat monetary system and corrupt political leadership will likely lead to increased financial and political disorder - and possible electrical outages and price increases. I'm often asked if a Tesla coil can be used to generate or gather power. No, a Tesla coil cannot harvest free energy, ambient energy, operate at "over-unity" or generate any useful power. If you're concerned about power outages and want to be energy independent, I recommend solar panels and / or wind turbines with batteries to supply electricity. Please be very cautious about "free energy" or "over-unity" scams.
These resources have helped me a great deal, and hopefully they can help you too.
Tesla Coil Mailing List
If you have a question about Tesla coils, it's probably been asked and answered in the searchable archive.
For several years Alan has provided high quality Tesla coil components and plans including "hard to find" and "one of a kind" items.
A pretty good overview of Tesla coils.
Octopart is a search engine for electronic parts.
Tesla Coil Web Ring
A list of Tesla coil orientated websites.
Steve's High Voltage
Interesting site with solid state musical Tesla coils, vacuum tube Tesla coils, Marx generators, induction heating and pulse power.
A good online JAVA design program from Bart Anderson.
A nice java circuit simulator applet. Tesla coil circuit is located in: Circuits -> Misc Devices -> Spark Gap
Lots of good Tesla coil information.
Teslamania, Bert Hickman's site about Quarter Shrinking, Lichtenberg Figures, Tesla Coils, Nikola Tesla, Pulsed Power, and big Arcs and Sparks
Tesla's autobiography - My Inventions
Tesla recounts his life in his own words. This text was first published in Electrical Experimenter magazine in 1919.
Matt's Tesla coil website (Swedish ONLY!)
Download a video of my Tesla coil producing 4 foot arcs.
You can view a couple pictures of my Tesla coils.
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