What's the best way 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. 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.
Should I build a Tesla coil for a Science Fair?
I don't recommend building a Tesla coil for a science fair. Safety can be a big issue. Even small Tesla coils can generate very dangerous voltages and currents. You'll have to restrict access to the area around the Tesla coil and constantly watch it - which is often impractical. The Tesla coil will need to be properly grounded, which can be difficult at science fair locations. Tesla coils will often have little problems that creep up, usually just before the science fair. Most of the time when people build their first Tesla coil the results are not very impressive. Sometimes finding parts can take quite a while, and the science fair will not wait for you.
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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