Tesla coil Instructables are not uncommon--I've written one myself--but in the following Instructable I'd like to not only describe building a simple upright coil, but also suggest some easy ways to assemble Tesla system components. Sometimes the parts of a Tesla coil system are harder to get than the coil itself. Then, at the end, I will demonstrate (in a small way) how Tesla coils can transmit electrical power through the air without wires.
The essence of this Instructable is simplicity rather than brute power or maximum efficiency. Because my coils are small, indoor models, I prefer to follow a modular method of building them. Most Tesla coils are unitized--everything packaged together in a single unit, just plug and play. I like to build in modular fashion so I can switch components around, try different coils, capacitors, or power supplies. Consequently my designs are clipped together with alligator clips and length of high voltage wire. If you
prefer the unitized approach, you can certainly adapt this design that way.
This Tesla coil system consists of these parts:
A high voltage (7,500 volts, 30 milliamps) AC transformer
A pressurized spark gap
A capacitor array
The coil itself, consisting of a primary and secondary coil on some kind of supporting
frame.
A "top load," or terminal
Wire to connect everything
Optional components you will want include a variable transformer (variac), and a small
hose-type vacuum cleaner.
Fluorescent light tubes, with stands
Each of these topics will covered on a separate page.
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Signing UpStep 1: Power supplies
This may be the most expensive part of your Tesla coil system. You will need an AC transformer of at least 3,000 volts at 30 milliamps to get the spark gap to fire, and more is better--within reason. Once you exceed 15,000 volts at 60 mA, you're leaving the indoor, tabletop arena and graduating to garage maniac status. This system is designed around a 7,500 volt, 30 mA neon sign transformer.
Until a few years ago, most neon signs were powered by heavy transformers potted in insulating tar. Nowadays concerns for safety (and liability) have made the old heavyweight NST obsolete. Modern neon power supplies are light, solid state units with Ground Fault Interrupt (GFI) protection. This is all very well if you're trying to light up a Michelob sign, but GFI power supplies won't work in a Tesla coil system. GFI is designed to stop just the sort of continual sparking a Tesla coil requires, so avoid modern neon power supplies. If you can't tell by the label if a transformer has GFI, try this rule of thumb: if the unit is small and light, it has GFI and won't work on your Tesla coil. If it's heavy as lead and almost as big as a cinder block, it will.
Other power supplies can be used. Oil burner ignition transformers (OBITS) can often be had cheaply. They almost always come rated at 10,000 volts at 23 mA. As with neon sign transformers, the newest OBITs now come with solid state circuitry and GFI. Pay close attention to make sure you don't get stuck with a useless GFI model.
Some coilers use microwave oven transformers. My advice is, DON'T. MOTs, as they are called, are rude, crude, and develop lethal amounts of current. If you don't know what you're doing, you can easily harm yourself or others. Until you've learned a lot more about electrical engineering, leave MOTs alone.
Car ignition coils are sometimes used to power Tesla coils. Ignition coils have to be driven by some kind of circuitry, either a 555 timer and associated parts, or even by something as simple as a household dimmer switch. This can be a fun project on its own.
Tesla coils can be powered by DC, but that's a different topic not covered here.
For best and simplest results, get your hands on a neon sign transformer (NST). All the ones I own I got off eBay pretty cheaply. They're heavy and can be expensive to ship, so if your budget is really tight, try a local sign shop. Many businesses are still switching over to electronic GFI power supplies and discarding their old NSTs. You might get a bargain if you offer to take an old-style NST off their hands.
Many NSTs come without power cords. When I salvage parts from old microwave ovens, one thing I always keep is the sturdy, three-wire oven power cord. These are easily adapted to NSTs.
One thing to remember about using NSTs: never move or lift an NST by the ceramic terminals! They're brittle, and they can crack or snap right off, then you've got nothing but a doorstop. Always lift NSTs by the case. One thing you can do to improve the portability of an NST is mount it on a base. I put my 7,500 volt Allanson NST on a shellacked pine plaque, fitted with four rubber appliance 'feet.' This insulates the NST from the tabletop, and gives me a handy place to grab and lift it.
It happens my Allanson unit has a pull-chain on-off switch. This is unusual. Most NSTs I've seen do not have on-off switches. Once you have grafted on a power cord, the best way to handle the NST is through a variac (a variable transformer), or an isolation transformer (see "Variacs and Vacuum Cleaners"). Failing those, you may have to use a wall socket controlled by a wall switch, or else put together a switch using a household wall switch mounted in a utility box.
Until a few years ago, most neon signs were powered by heavy transformers potted in insulating tar. Nowadays concerns for safety (and liability) have made the old heavyweight NST obsolete. Modern neon power supplies are light, solid state units with Ground Fault Interrupt (GFI) protection. This is all very well if you're trying to light up a Michelob sign, but GFI power supplies won't work in a Tesla coil system. GFI is designed to stop just the sort of continual sparking a Tesla coil requires, so avoid modern neon power supplies. If you can't tell by the label if a transformer has GFI, try this rule of thumb: if the unit is small and light, it has GFI and won't work on your Tesla coil. If it's heavy as lead and almost as big as a cinder block, it will.
Other power supplies can be used. Oil burner ignition transformers (OBITS) can often be had cheaply. They almost always come rated at 10,000 volts at 23 mA. As with neon sign transformers, the newest OBITs now come with solid state circuitry and GFI. Pay close attention to make sure you don't get stuck with a useless GFI model.
Some coilers use microwave oven transformers. My advice is, DON'T. MOTs, as they are called, are rude, crude, and develop lethal amounts of current. If you don't know what you're doing, you can easily harm yourself or others. Until you've learned a lot more about electrical engineering, leave MOTs alone.
Car ignition coils are sometimes used to power Tesla coils. Ignition coils have to be driven by some kind of circuitry, either a 555 timer and associated parts, or even by something as simple as a household dimmer switch. This can be a fun project on its own.
Tesla coils can be powered by DC, but that's a different topic not covered here.
For best and simplest results, get your hands on a neon sign transformer (NST). All the ones I own I got off eBay pretty cheaply. They're heavy and can be expensive to ship, so if your budget is really tight, try a local sign shop. Many businesses are still switching over to electronic GFI power supplies and discarding their old NSTs. You might get a bargain if you offer to take an old-style NST off their hands.
Many NSTs come without power cords. When I salvage parts from old microwave ovens, one thing I always keep is the sturdy, three-wire oven power cord. These are easily adapted to NSTs.
One thing to remember about using NSTs: never move or lift an NST by the ceramic terminals! They're brittle, and they can crack or snap right off, then you've got nothing but a doorstop. Always lift NSTs by the case. One thing you can do to improve the portability of an NST is mount it on a base. I put my 7,500 volt Allanson NST on a shellacked pine plaque, fitted with four rubber appliance 'feet.' This insulates the NST from the tabletop, and gives me a handy place to grab and lift it.
It happens my Allanson unit has a pull-chain on-off switch. This is unusual. Most NSTs I've seen do not have on-off switches. Once you have grafted on a power cord, the best way to handle the NST is through a variac (a variable transformer), or an isolation transformer (see "Variacs and Vacuum Cleaners"). Failing those, you may have to use a wall socket controlled by a wall switch, or else put together a switch using a household wall switch mounted in a utility box.
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I built my own Tesla coil web page. Hope you like it.
http://www.twotowers.com/tesla/tessie_1_tesla_coil.html
Steffan
I love your "Instructable"! You use of suction to quench the spark gap was very helpful. I did not use your design, but rather modified the design I am using with a 120V computer fan, sucking (rather than blowing) air onto the spark gap. My spark output doubled! Thank You!
I completely disagree however about the necessity of a safety gap. At least with a larger NST. My TC is powered by a 15,000V 60mA NST. I fried my first NST after about 5 minutes of operation because of a voltage spike from the primary and secondary coil. I do recommend implementing a safety spark gap in your coil! The safety gap installs across the capacitor. Depending on how you assemble your MMC, this can be very easy to make and adjust.
I would be happy to upload a photo of my MMC capacitor if anyone wants to see it. I got the idea for my MMC from www.thegeekgroup.org. The Geek Group is another great resource for anyone wishing to build their first tesla coil. They have a series of videos that walks you through the whole process. They skip over a couple details in their videos that I believe are important, but it's mostly all there. I also used their idea for a secondary coil winding jig. With someone operating the variable speed drill motor at one end of the jig, I was able to wrap 33 inches of secondary coil in about 10 minutes.
Thanks again!
There's nothing wrong with using a safety gap. I would under other circumstances. One reason I have never needed a safety gap is that I use fairly small NSTs--typically 7,500 V. They are current limited, and I always power them through GFI outlets via a variac or isolation transformer. Because I do almost all my experiments in my kitchen, I keep things small scale. I've never burned out a transformer or damaged anything except for toasting a few inappropriate capacitors. A 15KV/60mA NST is a bit of a brute to fire up inside the house.
Hardcore coilers prefer Cornell-Dubilier 942 series flash rated caps. They're rather expensive and not always easy to find. At the power levels I run, ceramic doorknob caps work fine. I also make my own dry Leyden jars--see my Instructable for Leyden Jar Battery for Tesla Coils. Those have never failed me.
Paul
Peace
Paul
I think the copper tube coil around the base would be better than insulated wire to enable tuning primary/secondary. I used at 15k NST. Never reached much corona from terminal, but I figure that was a tuning issue. Work in progress.
Watch a demo of my coil:
https://vimeo.com/63262916
Also article I wrote afterwards on Tesla:
http://pgavdestinations.wordpress.com/2013/04/22/nikola-tesla-a-world-without-wires/
Copper tubing be too thick for a small coil like this. It might be hard to get a good number of turns if you use a helical form. (That's why a lot of coilers make flat spiral primaries). You can of course cut tuning notches in the insulation of your primary. I prefer to vary the capacitance to achieve tuning. I also vary my top load to affect tuning too. Good luck!
Paul
Tony
Paul
Thank you for watching the video. What may not be apparent is that during the test, the corona discharge began to lose power to nil output. In the video you can see the capacitors begin to flame out (right-hand side of visual). This would seem to coincide diminished output from terminal. For this demo, the system was grounded as lower end of secondary to bottom end of primary. I did not use the TeslaMap, but certain I was under capacitance. I believe I was using 5 doorknob caps at 530 pf's each. Are doorknob caps a good choice for a small Tesla coil like this one? I had also tried salt water filled leyden jars, but discovered I had built them incorrectly as they seemed to not carry a charge. Surprised that you discourage the copper coil. I was thinking 1/4" copper tube turned 6x into a 30 deg angle (cross section). Not better? The assembly is actually in an exhibit at the moment so my tests are on hold for the moment.
BTW, have you seen the work that these guys are doing Teslatronix? http://www.teslatronix.com/
Thanks again Paul.
Tony
Paul
It is not uncommon to add a third coil to a Tesla coil system. This is called a magnifyer, or extra coil. Tuned properly, it can vastly increase the output. There's no reason to actually series-connect full coils through; I don't believe that would work. As for variable frequency generators, do you mean a variable frequency oscillator, or some kind of audio equipment?
PBT
PBT
I have no experience with DC coils, and that's what flyback transformers put out, high voltage DC. People do make battery powered Tesla coils, but it takes 12 volts at car battery levels to do it. I would check around for advice on DC coils. All my efforts have been made with household AC current.
Good luck,
Paul
PBT
Paul
I can't remember where but I remember you offering a high voltage soviet era capacitor for sale- do you have a way of contacting me about this?
thanks, OzL
Paul
PBT
TeslaMap: http://www.teslamap.com/download.html
JavaTC: http://www.classictesla.com/java/javatc.html
Paul
Total for Tesla coil system, $51.50. This does not include the fluorescent tubes, etc.
Another benefit of building the coil modular fashion is that the components are easily reusable in other projects.
Paul