Introduction: How to Build a 1.1 Million Volt Tesla Coil!
From wirelessly powered lighting to wireless chargers and even wireless smart homes, wireless transmission of power is an emerging technology with countless applications.
A light bulb powered with no wires? A cell phone charger that doesn't need to be plugged in? A home with no plugs, no wires and everything just 'works'? It's not magic, it's no mystery, it's science!
Let's get started!
*This guide will be updated once I am finished with this project
Various 3D Printed Parts Attached
(1) 12kV Neon Sign Transformer (NST), see picture above (eBay)
(1) Line Filter (FN2030B-3-06, Digi-Key)
(1) 300V Toggle Switch (https://www.amazon.com/gp/product/B01IYKSLCG/ref=p...
(2) 5/16" - 18 x 3" Carriage Bolts (Home Depot)
(6) 5/16" - 18 Hex Nuts (Home Depot)
(1) 120 mm PC Cooling Fan (https://www.amazon.com/gp/product/B07D493BDX/ref=p...
(1) 8 x AA Battery Holder (https://www.amazon.com/gp/product/B011WOKCPA/ref=p...
(40 + 1) 0.15 microfarad High Voltage Capacitors (Cornell Dubilier 942C20P15K-F, Master Electronics)
(40 + 1) 10 megohm High Voltage Resistors (HVR3700001005FR500, Digi-Key)
(1) Generic 5 gallon Bucket (Walmart)
(1) Roll of 16 AWG Bare Copper Wire (Amazon)
(80 + 5) 1/4" - 20 x 2" Hex Bolts (Home Depot)
(320 + 5) 1/4" - 20 Hex Nuts (Home Depot)
(320 + 5) 1/4" Flat Washers (Home Depot)
(160 + 5) 1/4" Lock Washers (Home Depot)
(1) Arduino Uno with jumper wires (Amazon)
(1) Hall Effect Sensor (US5881LUA-AAA-000-BU, Digi-Key)
(2) 1/2" - 13 x 4" Hex Bolts (Home Depot)
(4) 1/2" - 13 Hex Nuts
(50 ft) 1/4" Soft Copper Tubing (https://www.amazon.com/gp/product/B01EZ223TE/ref=p...
(1) #2 AWG Flex Copper Compression Lug (https://www.amazon.com/gp/product/B00B5O795O/ref=p...
(2000 ft) 24 AWG Enameled Copper Magnet Wire (24SNS2.5, Remington Industries)
(1) 4.5" x 4' PVC Pipe
(2) 4.5" PVC End Caps
(1) 4" - 8' Aluminum Dryer Duct (https://www.amazon.com/gp/product/B00009W3GV/ref=p...
(1) 12" x 24" - 26 AWG Plain Aluminum Sheet Metal
(20 m) 14 AWG 30kV High Voltage Wiring (https://www.amazon.com/gp/product/B01IX3B8YC/ref=p...
Heat Shrink Wire Connector Kit (https://www.amazon.com/gp/product/B06VW8LJFN/ref=p...
(30 ft) 16 AWG Generic Two Line Wiring (Home Depot)
(30 ft) 14 AWG Three-Pronged (Home Depot)
Braided copper wire
(1) 5/8" x 8' Copper Ground Rod (Home Depot)
Optional for Terry Filter:
(12 + 1) 10 megohm High Voltage Resistors (HVR3700001005FR500, Digi-Key)
(12 + 1) 0.0033 microfarad 1.6kV Film Capacitor (ECW-H16332JV, Digi-Key)
(2) 1 kilohm 100W Resistor (HSC1001K0J, Digi-Key)
Optional for NST:
(1) 66.3 microfarad Power Factor Correction (PFC) Capacitor
Soldering iron and solder
Drill and drill bits
Hacksaw for cutting PVC
Wire strippers, wire cutters, and pliers
Measuring tape, caliper, ruler, etc.
Screwdriver, wrenches, etc.
SDS-Plus Hammer Drill with Ground Rod Bit
* The "1" in (40 + 1) means that it is recommended to purchase an extra part in case one is defective
- PVC Jig v8.stl
- Secondary Holder v2.stl
- Primary Coil Holder v7 Body 1.stl
- Primary Coil Holder v7 Body 2.stl
- Primary Coil Holder v7 Body 3.stl
- Primary Coil Holder v7 Body 4.stl
- Primary Coil Holder v7 Body 5.stl
- Primary Coil Holder v7 Body 6.stl
- Primary Coil Holder v7 Body 7.stl
- Primary Coil Holder v7 Body 8.stl
- Gear Bearing.stl
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: How Does It Work?
- The Tesla Coil is essentially a very big transformer. A high voltage power supply, the NST (Neon Sign Transformer), charges up the MMC (Multiple Mini Capacitors. These high-voltage capacitors act as a battery for the coil). When the capacitor reaches a high enough voltage, the spark gap fires. The spark gap is like a switch. It turns on when the voltage gets high, and turns off when the voltage gets low. When the spark gap fires, it closes a circuit connecting the primary coil and the MMC. The energy stored up in the MMC dumps into a 1:100 step-up transformer. The primary coil (aka primary) is made of about 10 turns of thicker copper tubing. The secondary coiling is composed of around 1000 turns of thin wire. The MMC feeds in 12,000 volts and outputs 1,100,000 volts.
- Although the theory of operation of a Tesla Coil may seem simple, this is only part of the full explanation. The Tesla Coil transformer is based more on resonance than solely on turn ratio. When the spark gap fires, the electric charge in the MMC transfers to the primary, and then back to the MMC, and then back into the primary. This is called resonance, which is caused by the Alternating Current produced by the NST. Alternating current means that the direction that the electrons are traveling reverses direction periodically. In the US, this direction reversal happens 60 times each second.
- In the case of a Tesla Coil, the MMC (C1) and primary (L1, an inductor) make up a resonator. In a resonator, a capacitor stores energy in an electrical field, and an inductor stores energy in a magnetic field. In this resonator, the MMC is the capacitor (electric field), and the primary is the inductor (magnetic field). The resonance frequency is C1 x L1. The secondary picks up some energy from the primary each time the primary charges up. The secondary (L2) and the top load (C2) make up another resonator. The top load acts as a very small capacitor, and the secondary is an inductor. The output terminal, which is the top load, gets an electric charge from the secondary. The resonance frequency for this resonator is C2 x L2. The magic happens when L1 x C1 = L2 x C2. This means both resonators resonate at the same rate (this is tuned by adjust the tap on L1. This will be further explained in Step 17). When this happens, the energy in L2 builds up gradually with each cycle.
- This process is similar to a person on a swing. Imagine the legs are a resonator, going back and forth at a certain rate. The swing and the person is another resonator, swinging back and forth at a certain rate. At first, the swing is not moving. The legs start going back and forth, and the swing starts moving. If done correctly, the legs change position at the peaks of the swing motion. This means they are resonating at the same rate as the swing is swinging. As each peak of swing motion is reached, the leg motion adds a little bit of energy to the next cycle so that the swing arc grows a little each time. In the same way, the resonator C1 x L1 acts like the legs, adding a little energy to resonator C2 x L2, the swing and person. After many cycles, the voltage in C2 gets so high that it just explodes as an electrical discharge in search of ground. ZZZZZZZAAAAAAPPP.
This ZAP is exactly what the Tesla Coil is going to do. 
Step 2: Designing Process
The TeslaMap program is the single most important program needed to design a Tesla Coil.
This Java-based program uses multiple equations that enthusiasts have crafted specifically for Tesla Coils. This program can be found on www.TeslaMap.com
This Instructable is written based on my design, feel free to design your own coil. However, you would need to purchase a different amount of parts. The general build process will still be the same. My design is attached.
Step 3: Safety
*Tesla Coils have killed people!*
Tesla Coils can induce seizures
Please make safety a top priority when working with a Tesla Coil.
- When working with Tesla coils you'll be exposed to very high voltages, charged capacitors, exposed wiring, strong electric and magnetic fields, fire dangers, ozone, ultraviolet light and loud noise.
- When running a Tesla coil be sure to have fresh air, hearing protection, and do not look directly at the spark gaps.
- Make sure that people or animals cannot inadvertently enter a dangerous area.
- Try not to work alone and never work when tired or under the influence of alcohol, drugs or medications.
- Have a fire extinguisher and safety glasses near.
- Tesla coils may interfere with cell phones, pacemakers, hearing aids, and any medically implanted devices.
- Never adjust Tesla coils when the power is turned on.
- High voltage capacitors may hold a charge long after power is turned off. Always discharge capacitors before adjusting a primary circuit.
- Make sure the metal cases of transformers, motors, control panels and other items associated with Tesla coils are properly grounded.
- Make sure that you are far enough away from the corona discharge so that it cannot strike you. Do not come in contact with metal objects which might be subject to a strike from the secondary.
- The low voltage primary circuit is extremely dangerous! These voltages are especially lethal to humans. Make sure these circuits are well insulated so users cannot come in contact with the A.C. line voltage.
- Never operate a Tesla coil in an area where there is standing water, or where a significant shock hazard exists.
- Spend some time laying out your circuits. Hot glue, electrical tape and exposed wiring are quick and easy, but could be lethal.
The arcs generated by a Tesla coil are dangerous. You can look, but do not touch!
The NST is especially dangerous because it supplies several thousand volts, and you'll be working in close proximity to it. It's easy to accidentally leave it turned on. Except for a very quiet humming, there's no indication its turned on. 
Step 4: Power Supply (NST)
The power supply is a transformers made for neon signs, and they are the second best option for a Tesla Coil.
The best option is a pole pig which can be found on power lines. However, these are much more expensive and harder to find compared to Neon Sign Transformers (NST).
An example NST can be seen in the picture above. I purchased this one off of eBay.
- Make a cut close to the male end (the one with prongs sticking out) of the 14 AWG extension cord
- Solder on a line filter given the "Line" side connected to the Male end and the "Load side connected to the rest of the extension cord. Make sure to connect the ground. If there is only one ground prong on the line filter, run a jumper wire across.
- Wrap each individual connection using electrical tape, then wrap this unit using electrical tape.
- Around two feet away from the line filter, carefully strip off a 6-inch section of wiring. Do NOT cut it.
- Cut ONLY the black wire. For the 16 AWG generic wiring, connect the one wire from one end to one of the black wires you just cut. Connect the other wire from the same end to the other black wire you just cut. After this, you should have the 16 AWG generic wiring leading away from the thicker extension cord.
- After confirming, solder all of the connection and wrap using electrical tape.
- With the free end of the 16 AWG generic wiring, connect them to a toggle switch. Solder the connection. Mount this toggle switch to the 3D printed toggle switch case (files attached)
- Using a multimeter, connect the "Hot" end (the one with the smaller prong and opening) from both the female and male ends of the thicker extension cord. Check that these two ends are connected whenever the toggle switch is on, and disconnected whenever the switch is off.
- Make a cut at the female end of the extension cord (the one with openings for a plug).
- Strip off a 6" section of wiring, and connect each of the individual smaller wires to a heat shrink wire connector. This will be used to connect to the NST, so make sure the wire connectors fit.
- The black wire ("hot") will connect to the "+" input terminal of the NST, and the white wire ("neutral") will connect to the other terminal. The green wire is the ground, which is connected the unmarked separate terminal.
- There should be two output terminals on either ends of the NST, they are the same, so it doesn't matter which side is connected to what part.
- Check your work, and make sure you wrapped everything with electrical tape.
When looking for an NST, you may find newer ones that are cheaper. However, these will not work for a Tesla Coil, since the current spikes produced will "trip" the GFCI (Ground Fault Circuit Interrupter).
The NST is essentially two coils of wire that uses inductance to step up the voltage while lowering the current.
The NST shown in the picture above has an output voltage of 12 kV
A good NST should be very heavy and only contain a primary and secondary windings and an iron core. The output frequency should be the same as the input frequency (50 or 60 Hz).
NSTs have shunts that will limit the current if the output is shorted.
The low voltage side should be wired through a line filter which is connected to the house or building mains.
A PFC cap (see Step 11) should be wired across the input terminals, but the NST can run without one.
Step 5: Primary Capacitors (MMC - Multi Mini Capacitors)
The MMC is essentially a battery pack for the Tesla Coil that acts as a temporary storage.
Be sure to wire bleeder resistors across each capacitor to dissipate the charge once the NST is shut off so there is no dangerous charge. Without these resistors, the charge will remain for months.
Check all resistors and connections using a multimeter.
- Find the 5 Gallon bucket, and take off the handle using pliers. Be careful, since the ends of the wire can be sharp.
- Mark 80 holes according to the measurements specified in the first picture.
- Drill out these holes using a 1/4" drill bit
- The top 40 holes will be for 20 capacitors wired in series, which means that they are connected end to end. This increases the voltage tolerance, but lowers the capacitance
- In order to compensate for the lower capacitance, another series must be added. The lower 40 holes will be another series of 20 capacitors. These two capacitors will be wired in parallel to increase the capacitance, and this does not affect the voltage tolerance.
- Before attaching the bolts, add the bleeder resistors. Put two flat washers, one lock washer, and then one nut on each bolt (in this order). Secure a 10 megohm resistor between two bolt units. Make 40 of these two-bolt units
- Push each unit through two holes you drilled out. Then, put on two nuts, two flat washers, one lock washer, and one more nut (in this order). Do not tighten anything yet.
- Grab a 0.15 microfarad capacitor. Wrap the two capacitor leads around each of the two bolt units. You will need to cut off the excess wire.
- Using 16 AWG bare copper wire, connect each of the capacitors in an alternating fashion.
- Check all electrical connections using a multimeter.
- Tighten using wrenches.
Step 6: Spark Gap
The spark gap is constructed using a 5" section of unused PVC pipe leftover from the secondary coil.
Often, the gap will continue to short even after the MMC voltage has fallen below the voltage needed to short the gap. This happens because the air between the gap becomes ionized when the gap shorts. The ionized air is more conductive and allows the gap to remain shorted. This can be prevented by blowing air through the gap. The goal of this is to blow the ionized air out of the gap. 
- Drill two 5/16" holes in the middle, and on opposite sides of the PVC pipe.
- Insert two 5/16" carriage bolts, these will act as electrodes.
- Hold the each bolt in place with one nut on the inside, and one nut on the outside of the PVC
- The wiring will be connected between two more hex nuts.
- Attache a 120 mm computer fan using duct tape, it doesn't have to be extremely tight.
- Wire the computer fan to the battery connector included with the holder.
- Tighten everything using wrenches.
- Tune the spark gap. (See step 16)
Step 7: Primary Coil
This will be constructed using 3D printed parts and the 1/4" copper tubing. 
Step 8: Secondary Coil
The secondary coil and the top load create the secondary resonator. The secondary coil also couples to the primary coil and transfers power from the primary resonator to the secondary resonator.
To wind the secondary coil, you will need to make an Arduino Uno powered tachometer.
- Connect all the components according to the first image.
- Make sure the sensor is connected through 3 jumper wires
- Use the attached program. You can optimize it to suit your needs.
- Test that everything works using a Neodymium magnet
This tachometer uses a Hall Effect Sensor. Whenever a magnet passes over the sensor, it outputs a "low" signal. When there's no magnet over the sensor, it outputs a "high" signal. The Arduino counts the number of times the signal switches and displays the number on the LCD. The LED also lights up each time the signal switches.
- First, print the Gear and PVC Jig using a 3D printer.
- Secure one Jig using duct tape. The Gear will fit inside of the Jig. If the fit is too loose, use some masking tape around the gear to increase friction and diameter.
- Drill one 1/2" hole in the center of 2 PVC end caps.
- Insert 1/2" bolts through these holes, and secure using nuts
- Fit these end caps over the ends of the 4.5" x 4 ft PVC pipe
- Next, insert the unit into the secure jig. Then, insert the other Jig.
- Secure the two Jigs.
- Attach the neodymium magnet onto the PVC pipe using masking tape.
- Tape the Sensor under the PVC pipe near the Jig. If the sensor isn't high enough to reach the magnet, use something non-magnetic to increase the height.
- Attach a drill to the end to help spin the contraption
- Check that the tachometer works.
- To start the winding process, spin the drill and use a sharpie to mark a "starting line"
- Tape the 24 AWG Magnet Wire down using a piece of masking tape, leave enough tape on the end to remove later. Also, leave a few feet of excess wire for later use.
- Wrap the wire 928 times.
- Leave another few feet of excess wire.
- After finishing, secure the ends with superglue.
Step 9: Top Load
This will be constructed using the aluminum dryer duct. 
Step 10: Line Filters
A line filter is required since it can prevent high voltage spikes from traveling back into the house or building wiring.
Line filters usually consist of a capacitor to shunt the high frequencies to ground. Most will also use inductors to cut down the high frequency spikes. Some may have MOVs (metal-oxide varistors) to shunt voltage spikes to ground. 
Step 11: PFC Capacitors
Power factor correction (PFC) capacitors are used to correct the power factor of the AC supplied to the NSTs. When a circuit contains a large inductance or capacitance the voltage and current will be shifted out of phase, resulting in reduced efficiency.
The power factor will be degraded due to the large inductance in the NSTs. The capacitance in the PFC cap will realign the voltage and current phases.
The PFC capacitance does not have to be exactly matched to the transformer.
Be sure to use only "run" type capacitors, as opposed to "start" type capacitors. Start capacitors are designed to only be used for short periods of time, to start a motor for example. They will overheat and possibly explode if run continuously. Electrolytic caps should not be used as PFC caps, they'll also heat up and pop. PFC caps can be found in salvage / recycling centers on AC motors, washing machine motors, refrigerator motors, etc. 
Step 12: NST Protection - Terry Filter
The wire in the NST secondary coil is very thin and easily shorted by high voltage spikes generated in the primary circuit. A spark gap and a low pass filter will help protect the NSTs from voltage spikes and premature death. 
Step 13: Chassis
This will be constructed from a cabinet. 
Step 14: Wiring
All wiring before the NST should be 300 V wiring, but after the NST, all should be High Voltage Wiring.
Wires can be connected to parts using heat shrink connectors. 
Step 15: Grounding
Grounding is very important for safety and proper operation of a Tesla coil.
The Tesla coil should have two separate grounds. The first ground is the house or building ground (also known as mains ground). This is the green wire in the electrical outlets. The second ground is RF ground.  
For the RF ground, pound an 5/8" x 8' Ground Rod into the ground using an SDS-Plus Hammer Drill.
Step 16: Adjusting Spark Gap
The spark gap should be adjusted so that it is at its widest distance apart but will still spark. 
Step 17: Tuning