Introduction: How to Build a 1.1 Million Volt Tesla Coil! : 19 Steps (with Many Pictures)
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!
*Figure numbers for pictures are shown once you open up the picture in the top left corner
- 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
3D Printed Parts:
Various 3D Printed Parts Attached
Print using: a perimeter of 5, infill of 15%, layer height of 0.2mm. This will make the prints the strongest.
(1) 12kV Neon Sign Transformer (NST) (eBay)
(1) Line Filter (FN2030B-3-06, Digi-Key)
(1) 300V Toggle Switch (https://www.amazon.com/gp/product/B01IYKSLCG/ref=p...
(1) 66.3 microfarad Power Factor Correction (PFC) Capacitor (not required, a smaller one is acceptable)
(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' Semi-Rigid Aluminum Dryer Duct (non-shiny type).
(1) 12" x 24" - 26 AWG Plain Aluminum Sheet Metal
(8 ft) Shock Cord (bungee cord without hooks)
(1) 1/2" - 13 x 6" Carriage Bolt
(1) Luxor EC22 18x32 Cart with 2 Flat Shelves (Walmart)
(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) 16-2 AWG Generic Two Line Wiring (Home Depot)
(30 ft) 14 AWG Three-Pronged Extension Cord (Home Depot)
(1) #4 - 2/0 Wire Range Morris Products I Beam Ground Clamp
(2) #8 - #4 Wire Range Morris Products I Beam Ground Clamp
(1 roll) Electrically-Conductive Copper Foil Tape (must be electrically-c
(1) 5/8" x 8' Copper Ground Rod (Home Depot)
(30 ft) 8 AWG THHN Stranded Wire (Home Depot)
(12 + 1) 10 megohm High Voltage Resistors (HVR3700001005FR500, Digi-Key)
(12 + 1) 0.0033 microfarad 1.6kV Film Capacitor (ECW-H16332JV, Digi-Key)
(14 +1) 1800V MOV (ERZ-V10D182, Digi-Key)
(2) 1 kilohm 100W Resistor (HSC1001K0J, Digi-Key)
(1) Flexible Prepunched Breadboard, NPTH (FIT0576, Digi-Key)
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
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 or when ANYTHING IS PLUGGED IN!!
- 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 Fig. 6 above. I purchased this one off of eBay. Input wiring of NST can be see in Fig. 11.
- 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. This way they won't short.
- 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 Fig. 6 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 (see Step 10) which is connected to the house or building mains.
A PFC cap (see Step 11) should be wired in parallel across the input terminals, but the NST can run without one. This is shown in Fig. 11b.
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. This is the capacitor in the primary resonator, which will transfer power to the secondary resonator.
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 theoretically remain forever.
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 Fig. 12.
- 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.
Add Input and Output terminals:
- Drill holes as shown in Fig. 12c
- Connect as shown in Fig. 12d using 14 AWF bare copper wire
- Cover as shown in Fig. 12c and Fig. 12d using liquid electrical tape. This is done so it wouldn't spark between the two terminals.
- The bottom outside terminal will be connected to the Spark Gap
- The top inside terminal will be connected to the Fixed Primary Coil terminal. (This will be discussed in Step 14)
- Consult the circuit diagram in Fig. 12e for further assistance.
The MMC Array must be connected as shown in Fig. 12e where a terminal is closer (by length of wiring) to the top series of capacitors while the other terminal is closer (by length of wiring) to the bottom series of capacitors. This is to limit the effect of the resistance of the wiring.
Step 6: Spark Gap
The spark gap is a very fast switch that switches the primary resonator on and off 60 times a second because of the alternating current.
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)
Spark Gap Fan:
- Tape the battery pack on top of the spark gap as shown in Fig. 14. This is to prevent sparks from power to the batteries.
Step 7: Primary Coil
The primary coil is the inductor in the primary resonator. This will transfer power to the secondary resonator.
This will be constructed using 3D printed parts (Fig. 15) and the 1/4" copper tubing (Fig. 15b). 
- Assemble the 3D printed parts using superglue Fig 15b
- On one end of the copper tubing, crimp an L-shaped lug into place.
- Bend enough length of the end of the copper tubing so that it will go through the top of the chassis as seen in Fig. 16b and Fig. 16c. There should be an inch of clearance for connecting wiring.
- Set the copper tubing into place, use a rubber hammer if need
- Start close to the inside cylinder and continue winding until you reach the outermost coil
- The final result should be similar to Fig. 16
Strike ring will be used to protect the primary coil from the sparks from the top load
- Use a separate piece of copper tubing and set it in the higher groove on the assembled 3D print as shown in Fig. 16
- Make sure that the two ends of the strike ring are NOT connected, or else it will affect inductance of the primary coil.
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.
Next, spray paint the secondary coil with lacquer spray paint to protect the enamel of the wiring from being scratched. This spray paint will also "glue" the wiring to the PVC pipe and prevent any movement.
- Cover everything except for the wiring part of the coil with paper and seal off with masking tape. (Fig. 19)
- Be sure to attach a drill to the winding jig keep the secondary coil turning to prevent uneven spray painting
- When spray painting indoors, wear a respirator to prevent breathing in aerosol gases. (Fig. 19b)
Step 9: Top Load
The purpose of the Top Load, aka metal donut, is to act as a the capacitor in the secondary resonator. It also acts as an electrode where sparks will be emitted from.
This will be constructed using the aluminum dryer duct (Fig. 20) and aluminum sheet metal. 
Cut two 11" diameter circular pieces of aluminum sheet metal. Using a CNC Mill helps a lot with this process (Thank you Dr. P for this tip!).
- Using one of the previously drilled PVC end caps from the secondary winding step, insert a 1/2 x 6" carriage bolt.
- Attach the two aluminum sheets as shown in Fig. 21. The two aluminum sheets are separated by 8.8 cm.
- Wrap the aluminum dryer duct around the mold to form a circular metal donut. Make sure it's as close to a circle as possible. (Fig. 22)
- Insert a piece of shock cord inside the dryer duct, and tie it down to secure the donut. (Fig. 23) This cord will stay in the toroid.
- Tape everything together using electrically-conductive copper tape. Limit number of sharp edges, as they will disrupt the electric field formed by the toroid. (Fig. 24)
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. (Fig. 25)
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. 
This is wired in series with the NST. The farther away from the Tesla Coil, the better. This means the line filter should be placed closer to the original 120V power source to limit interference. (Fig. 25b)
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.
PFC Capacitors are special and are very different from normal capacitors. DO NOT use normal capacitors as they will explode and usage is very dangerous.
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. 
This is wired in parallel with the NST. (Fig. 28)
- Solder the two terminals of the PFC Cap to a 12 AWG - 2 generic wiring. (Fig. 28)
- This will then be wired to the NST in parallel. (Fig. 29)
- Attach the PFC cap to the Chassis using duct tape. (Fig. 28c)
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. This filter is invented by Terry Fritz, hence the name Terry Filter.
The Terry filter will prevent NST from shorting by using capacitors and MOVs.
Capacitors shunt high frequencies to ground Resistors decouples NST from primary circuit Spark gaps and MOVs (Metal Oxide Varistors) shunt high voltage spikes to ground. The resistors are bleeder resistors that dissipates the charge on the capacitors over several seconds to prevent the capacitors from holding a dangerous charge during transportation.
- Solder everything onto the flexible prepunched breadboard according to the schematic in Fig. 31 (Fig. 32, 33)
- Add insulation with liquid electrical tape (Fig. 34)
- The completed Terry Filter is shown in Fig. 35
The safety gap is made using another 5" section of PVC pipe. The safety gap is a spark gap but is different from the main spark gap of the Tesla Coil. This gap only fires when needed to protect the NST. This gap is tuned so that it is the two electrodes are closest but not sparking when the NST is turned on and just connected to the Terry Filter and Safety Gap.
The Safety Gap is placed in a winding jig that serves as a base. Seen in Fig. 35
Step 13: Chassis
I used a plastic utility cart for the chassis that was difficult to find. You can use anything including cabinets; however, avoid metal. Preferably, the chassis should have wheels for ease of transportation.
The chassis top must be flat so the primary coil that will be set on the chassis will not be hanging on the edges with no support under the middle. For the utility cart I used, section of the edges that the primary coil overlapped were Dremeled (sanded using a Dremel) so that it would be at least flat or lower than the rest of the surface. (Fig. 37b)
Fig. 36b shows the underside of the chassis.
Optional: Add non slip mats to both shelfs to prevent parts from moving.
Drill holes in the top shelf of the utility cart according to Fig. 37b. The holes in a circle should be under the strike ring between each leg of the 3D printed assembly. They are labeled as such.
Step 14: Wiring and Placement
All wiring before the NST should be 300 V wiring, but after the NST, all should be High Voltage Wiring. I used 30kV high voltage wiring.
Wires can be connected to parts using heat shrink connectors. 
Wire according to the schematic in Step 1, Fig. 3
Place everything strategically in the chassis to use as little wiring as possible with optimally no crossing wires. Absolutely no wires should be touching; in fact, all wires should be at least 2 cm apart.
- Everything will be connected with heat shrink wire connectors.
- The fixed primary coil tap is the previously connected L-shaped lug, which is passed through a hole Dremeled in the chassis and connected to the MMC array. See Fig. 42.
- The adjustable primary coil tap and strike ring is connected to by using I-beam ground clamps. (Fig. 41)
- The RF ground wire is connected to the ground rod using another I-beam ground clamp. (Fig. 41)
- The bottom of the secondary coil is passed through a hole in the top shelf of the chassis and connected to RF Ground using a Twist Cable Connector. (Fig. 39).
- The top of the secondary coil is taped directly onto the toroid using electrically conductive copper tape. (Fig.40)
There are many different Tesla Coil schematics online that show either wiring the MMC or Spark Gap across the NST Outputs. Terry Fritz ran many tests and found that wiring the Spark Gap across the NST Outputs puts less stress on the NST coils. This is why you should always connect the Spark Gap directly to the NST. 
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.
To test if your ground works properly, connect a wire to one of the outputs of the NST. Bring the other end of the wire close to the grounding rod, and if it sparks, then the grounding rod works correctly. (Fig. 43b)
Step 16: Adjusting Spark Gap and Safety Gap
The spark gap should be adjusted so that it is at its widest distance apart but will still spark.  (Fig. 44)
On the contrary, the safety gap should be adjusted so that it is at its shortest distance apart without sparking. (Fig. 35, Step 12)
Step 17: Tuning
By tuning the Tesla Coil, the resonance frequency of the primary resonator is changed to match the frequency of the secondary resonator. This will make the coil the most powerful and increase the spark length.
- When operating the Tesla Coil, take note of the maximum spark length.
- Turn off the coil, and unplug it.
- Adjust the tap position of the primary coil along the outer coil as seen in
To make the Tesla Coil shoot one long spark instead of many shorter ones, find a long, sharp nail and tape it onto the coil using electrically conductive copper tape. This nail will produce a disruption in the overall electric field of the toroid, and the electric field on the tip of the nail will be the strongest. This will cause sparks to shoot from the tip of the nail. You can also make your own "nail" out of 14 AWG solid bare copper wire by sanding the tip of the wire into a very sharp point. The longer an sharper the wire is, the more concentrated the sparks will be. (See Fig. 46f in Step 18) Making your electrode would produce better results than buying a much shorter nail.
Step 18: FUN!!
Before having fun, check every connection using a multimeter. Also, REVIEW SAFETY IN STEP 3!!!!! This is very important!
Now you can fire the Tesla Coil! (Vid 1, Fig.46 a,b,c )
The reason why there is a larger spark to the left is because I put a sharp and thick copper wire on the left side of the Toroid. (Fig. 46f) The disruption in the electric field caused sparks to form from the tip of the copper wire (further explanation Step 17)
You can try putting a fluorescent light tube near the coil by setting it on something (Don't go near the coil!). It should light up! (See Vid 2, Fig. 46d, and Fig. 46e) The way this works is that the fluorescent light tube lights up whenever there is a potential difference between the two ends. When the light tube placed parallel to the electric field, there is a potential difference produced between the two terminals, which causes it to light up!
Step 19: Challenges and Skills Learned - Term II
This has been an extremely challenging experience.
- Terry Filter was very challenging to build and operate. The soldering part itself was hard, and I gained a much better understanding of how to solder. In fact, at one point, I even held two tools in one hand and the soldering iron in the other (See Fig. 33). Furthermore, the Terry Filter would spark each time I turned it on. This was due to a poor design choice of putting the two series too close together. To fix this, I used liquid electrical tape to provide more insulation.
- Cutting out two circular pieces of aluminum sheet metal was also very difficult. Thanks to Dr. P's help, I was able to learn to use the CNC-mill to aid me in the cutting.
- The L-Lug for the fixed primary tap was loose due to mistakes during assembly. I spent a few hours soldering the lug on to create a tight fit. (See Fig. 47).
- Another difficulty was figuring out the exact placement of everything in the lower shelf of the utility cart. I chose between 3 different methods of wiring. It turned out to be a very tight fit, which was unexpected since the cart is a fairly big chassis for a Tesla Coil.
- I failed the first time when I was making a toroid. I learned it the hard way that Aluminum Dryer Ducts unravel really easily after being cut.
- I also made another mistake making the second and final toroid. I covered parts of the toroid with very thin copper foil tape, which caused many disruptions in the electric field around the toroid. This caused it to shoot many smaller sparks instead of shooting one big spark out of the sharp copper wire on the toroid. This can be seen in Fig. 48. The spark shooting out of the sharp copper wire was much larger; however, optimally it would have been the only spark. If there is only one spark, it will be much longer since more of the charge is concentrated on the tip of the copper wire.
- When I was first spray painting the Secondary coil, the drill that was supposed to keep it turning stopped working. After a long dinner, there were beads over spray paint everything. However, this is not as detrimental as it seems since it only affects the cosmetics.
- I also tried several different designs for the MMC array, and I finally settled on the bucket design. This choice was crucial to my success since it allowed for more cooling of the capacitors, and it prevented unintentional sparks between individual capacitors.
All in all, making this coil is a wonderful experience and a combination of nearly all the building skills I've learned thus far. I also learned that constantly testing every component in every step was very important. While building the coil, I tested everything several times to confirm that they are operational. This was crucial to the success of the first run. Further, if the first test was not successful, it would be much easier to troubleshoot the problem. Finally, if I did not check everything dozens of times, the coil might have blown up. This would cost me a lot of time and money to rebuild, that is, if I survived the danger caused by the explosion.
Step 20: Future Upgrades
I was not able to get to these upgrades due to time and resource limitations
- Use another material other than PLA 3D prints for the primary coil for more structural integrity.
- Add a base under the Terry Filter, for example using acrylic plastic
2 years ago
Wow, this is awesome. I have sitting in my shed the heat exchanger from an old hot water tank, been meaning to try it as a Tesla coil primary for many years. So you have given me a bit more inspiration to actually give it a go.
Reply 2 years ago
A heat exchanger would work very well as a primary of a bigger Tesla Coil. If the heat exchanger is tall, though, it might not work with a smaller Tesla Coil. Most likely, the only sparks will be from the top load directly to the primary coil. I would definitely recommend a strike ring (in fact, all Tesla Coils should have one to protect the primary).
One solution is always to make the Tesla Coil bigger (and taller)! The taller it is, the more distance between the top load and the primary, which means a lesser likelihood of sparks directly to the primary.
Best of luck!