01270 747 008 (UK)
Tesla Coil SRSG 500Va 1 Spark

DIY SRSG Tesla Coil

DIY SRSG Tesla Coil

with synchronous rotary spark gap

Tesla Coil Big SparksThis Tesla coil runs from a 220V mains input at around 1kW to give an awesome display of arcs and sparks. It has been made with a large secondary coil so that the topload has sufficient elevation for some of the experiments it will be used for and so that it can be upgraded to higher power levels in the future.

The content of this page is for anyone with an interest in Tesla coils and high voltage. We have tried to explain everything clearly and with enough detail so that it can be understood by anyone with some basic knowledge of electronics. We have also included useful formulae and the calculated result of them based on the parameters of this Tesla Coil. Based on the information on this page you should be able to reproduce your own home made Tesla Coil (at your own risk) so there is no need to buy any Tesla coil plans when you can get free Tesla Coil plans here! There are also other more technical details included on this page so that it is still of interest to those who are already familiar with building Tesla coils.

If you are not familiar with Tesla Coils, you could read our page that describes how a Tesla coil works.

high voltage danger logo

WARNING: Tesla Coils are very dangerous high voltage devices!

If you do decide to build a Tesla coil or use any of this information, you should make sure you understand all the safety precautions needed. RMCybernetics are not responsible for anything you do as a result of reading this information.

Tesla Coil Big Input Voltage 220V AC
Power Consumption 1000W Max
Max Arc Length 74cm
Capacitor 20kV 0.06uF
Spark Gap SRSG(100BPS)
Primary Turns 3.5(Tuned) – 10 Available
Secondary Turns 550(0.56mm wire)
Secondary Height 61cm(Windings only)
Secondary Diametery 11cm
Topload Double Sphere
Special Features Secondary Gas Feed

So what does a SRSG Tesla Coil do?

Tesla Coil is used to convert relatively low voltage (like from the mains) to a very high voltage which oscillates at very high frequency. The result of this is lightening like electrical discharges from the top of the device. SRSG stands for Synchronous Rotary Spark Gap. This term describes the way in which the power is switched in the Tesla Coil. These devices were invented over 100 years ago which was before modern semiconductors and electronics. This meant that to switch power it was necessary to use mechanical methods like the SRSG.

This SRSG consists of two stationary electrodes and four interconnected electrodes on a spinning wheel. As the wheel spins, the electrodes pass by the stationary ones which briefly allows a spark to jump and transfer some power. This happens repeatedly as the wheel spins around.

The motor used to spin the wheel is a synchronous motor which means that it spins in phase with the mains frequency. In the UK this frequency is 50Hz which will cause the motor used here to turn 25 times per second.

The capacitor used in this Tesla Coil will be charged 100 times per second so we want the spark gap to switch the power every time the capacitor is charged. Having four electrodes on the wheel means that at every quarter turn of the motor, the electrodes line up and allow the energy transfer.

Tesla Coil SRSG 500Va 1 Spark Tesla Coil SRSG 500Va 2 Spark Tesla Coil SRSG 500Va 3 Spark

The photos above show the coil running at about 500W

Tesla Coil SRSG KVa Spark

Here you can see an arc hitting a grounded rod about 70cm away. The coil is running at 1kVA.

Tesla Coil SRSG Kva 2 Spark

A long breakout point was needed to get good arcs due to the small topload

The parts used and what they do

For holding the components together

Tesla Coil BaseThe supports for the coils were made on a piece of wood which was dried and sealed before use. Even very dry wood can attract high voltage discharge to it, so it is important that it is kept very dry and sealed to prevent it from absorbing more moisture. Plastic is much better to use but can be expensive and harder to work with.

The supports for the primary coil were made by drilling a series of holes diagonally at equal distances in a block of wood. This was then cut down the center of the holes so that a series of grooves remain where the copper pipe of the primary coil would sit. These supports must be very well dried and varnished as the copper pipe could leak power into the wood.

The Grey pipe in the center is part of a 90 degree bend that fits into the push fit base of the secondary coil. This allows it to be mounted securely and easily.

Primary Transformer
Used to change the 220V mains input into 10,000V

Tesla Coil NST 100mA

The transformer used is a Ricci NST (Neon Sign Transformer) rated for 10kV 100mA from Signbuyer.co.uk. This transformer is quite compact and comes with built in ground fault protection (GFP). There are a wide range of neon sign transformers available from Signbuyer which would allow you to make Tesla coils like this one or smaller. If you want bigger sparks, you can use two transformers in parallel to double the output power.

The primary transformer is what will determine the input power (and therefore arc size) to the Tesla coil. 10kV 100mA gives a maximum of 1kVA. (VA is equivalent to Watts, but is used because things get a little more complex with transformers). You can calculate the approximate size of arcs you can expect from the Tesla coil based on the input power. The length calculated is the straight line distance is that measured between the arcs origin on topload to a nearby grounded object.

Arc Length

L(cm)= 4.3 x √P(VA)136cm

This formula assumes that all the power from the input is transferred to the arcs and is not wasted in the conversion process. In practice this is not possible but the value given by this formula is a good guide.

Tesla Coil PFCBased on the NST used in this coil the arcs theoretical limit is 136cm. The actual length we have got so far is 74cm. It may be possible to get more by having a tighter coupling between the primary and secondary coils but this would run the risk of causing damaging arcs between the coils.

NST’s have a small gap in the metal core which is used to limit the output current. This means that even with the output shorted, it wont overheat. Gapped transformers like these ideally should have a power factor correction (PFC) capacitor placed in parallel with its input. This serves to correct the shift in the phase of voltage and current caused by the large inductance of the transformer. It will work fine without it, but the power transfer will not be so efficient. The correct PFC capacitor can be calculated as follows.

PFC Capacitance

C = P/(2 x π x f (V2)) = 65.8uF

Where P = NST VA rating, V = NST input voltage, and f = mains frequency. It is not necessary to use the exact capacitance calculated, something less is fine.

It is common for people to remove the GFP when using the NST in a Tesla coil as the transformer is not connected to the mains earth anyway. It was left in for this coil as it can help prevent the transformer from becoming damaged if anything goes wrong.

Tesla Coil Terry FilterHigh Voltage Filter
Used to protect the primary transformer from damage cause by RF (high frequency) voltage spikes

The filter used is a common type of low pass filter known as a Terry filter which is often used in Tesla coils which are powered from an NST. The filter allows the 50Hz mains frequency to pass through easily but will provide a path to ground for the high frequency currents. It also includes a set of MOV’s which will short to ground if the voltage gets too high.

Resistors are mounted on heatsinks as they will get hot when in use. These and the other components must be spaced apart adequately so that sparks don’t occur between them.

To protect the 10kV NST used in this Tesla Coil, we used 14 of each of the following components; MOV/TVS – 1800V, Capacitors 1.6kv 3.3nF, Resistors 10M ohms 0.5W. In addition to these two 1k ohm, 100W resistors mounted on heatsinks are used. You can see how these are connected together in this Terry Filter Schematic. The the main schematics lower down to see how it is connected in the system.

Primary Capacitor
Used to store energy for releasing in pulses into the primary coil

Tesla Coil MMCTesla Coil CapacitorWith smaller battery powered Tesla coils the type of capacitor used is not too important. With larger coils like this it is important to use high voltage capacitors that are suitably constructed for handling large amounts of power. Large ones like shown below can be quite expensive so it is common to construct an equivalent capacitor from lots of smaller ones. This is known as an MMC. The one shown here was made by connecting fourteen 1500V 47nF polypropylene capacitors in series, then making 3 more identical strings. Each of these strings is equivalent to a 21kV 3.4nF capacitor. Connecting these four in parallel makes the overall capacitance 13.4nF. Usually a 10M resistor is placed across each of the small capacitors as a safety precaution. This capacitor was not used as it was too small for the NST.

The primary capacitor used was made by combining six 20kV 0.01uF pulse capacitors in parallel. This capacitance is about as large as the 100mA NST can charge between each firing of the spark gap. With a static gap this capacitor would need to be smaller, but because the spark gap used here is synchronous, a larger capacitor is possible.

The value of capacitance that will work best with the transformer is calculated based on the mains frequency and the transformers impedance. You can calculate the transformers output impedance based on its output ratings

NST Output Impedance

Z(ohms)= E / I = 100k ohms

Where E = NST Output Voltage and I = NST Output Current

Now we know the output impedance of the NST we can calculate its capacitive reactance. The capacitive reactance give us the value of capacitor that the NST can fully charge during each half cycle.

Primary Resonant Capacitance

C(r) = (1/(2 x π x Z x f)) = 31.8nF

Using a capacitor that matches the capacitive reactance of the NST is not recommended. This would cause a resonant condition that would cause the voltage to rise, possibly damaging the NST and the capacitor. This is not the case for other types of transformer, but for the NST you would use a larger capacitor to prevent this resonant condition occurring. The actual value depends upon the type of spark gap used and is calculated as follows;

Actual Optimum Capacitance
Static Spark Gap: 

C = C(r) x 1.618

Synchronous Rotary Spark Gap:
C = C(r) x 1.9 = 60.47nF

Where C(r) = the calculated resonant capacitance or capacitive reactance.

The capacitance of this capacitor combined with the inductance of the primary coil will determine the resonant frequency of the primary circuit. It is essential that this frequency matches the resonant frequency of the secondary coil so that energy can be efficiently transferred between the two and the voltage rise can occur.

Spark Gap
Used to discharge the capacitor into the primary coil by making and breaking a connection like a switch

Tesla Coil Rotary GapThe spark gap used here is a synchronous rotary spark gap. This means that a motor spins around, moving some connected electrodes past the two main electrodes so that it will make a connection as it passes and break it again as it moves away. The spark still needs to jump but it is just about 1 or 2mm. The motor turns around exactly 25 times per second and is in phase with the 50Hz mains current. The four electrodes fixed on the rotating wheel are electrically connected and will connect the capacitor to the primary coil 100 times per second. The position of the rotating electrodes must match perfectly with the mains frequency so that the connection occurs when the capacitor is fully charged (at the peak of each positive or negative half cycle). An external control was made for controlling the phase of the motor so that it can be matched for optimum performance when it is running.

Also included is a safety gap which is just some electrodes spaced at a set distance that will allow the capacitor to discharge into the primary coil if the for some reason the rotary gap is not working right. When the motors phase is matched exactly or is slightly ahead of the primary capacitors voltage the safety gap should not be firing.

Primary Coil
Used to transfer energy to the secondary coil from the primary capacitor

Tesla Coil PrimaryThe coil is made from standard 6mm copper plumbing pipe. This is quite soft so it is easy to wind into a coil shape.

Copper pipe is used because it is thick and has low resistance (more efficient) and it is also easy to clip a wire to different points around the coil when tuning.

Wood should be dried and sealed as the copper pipe will be at high voltage when running the coil. The 10kV present on the coil is enough to jump to any unsealed wood which could cause fire or just hinder the coils performance.

Tesla Coil Primary SideThe coil was wound in a conical shape to allow for a good coupling to the secondary coil. If the power is upgraded in future it would be necessary to add a grounded strike rail above this to protect it from being hit by the Tesla coils output. It may even be necessary to replace the coil with one of a flatter design.

Secondary Coil
Used to step the voltage up higher still so that arcs can be produced from the topload

Tesla Coil Secondary BaseTesla Coil Secondary CapsThe secondary coil was wound on a piece of standard 11cm diameter waste pipe. This piece had a push fit type connection at one end which would be used to mount the coil on the Tesla coils base.

Each end of the coil was terminated with a final winding made from copper tape for neatness and easy connection. This loop of tape should not be continuous as it would act like a shorted turn and waste energy. A small cut is made so that the copper tape acts like the final turn of the coil connecting the wire to the RF ground.

At the base of the coil, the connection for RF ground is made by taking a strip of copper tape down the side and a few cm up again inside the pipe. When this end is pushed onto the support it meets with a matching area of copper which is connected to the RF ground This makes it very easy to place the secondary onto the base and have the RF ground connected without any solder or screw connection .

The same method is used for connecting the coil to the topload.Tesla Coil Secondary Top

Tesla Coil Pipe WindingBecause this is an RMCybernetics Tesla Coil, we like to do it a little differently. Down the center of the secondary coil is a piece of 32mm drainage pipe. it is held in place by plastic discs which are epoxied in place. Around this central pipe is another pipe that is wound as a coil along its length. This pipe is about 20m long when uncoiled.

These pipes can be used for piping gasses or mechanical systems to the topload for performing various interesting experiments.

Tesla Coil Secondary Winding

The secondary coil was wound on a simple jig with a geared motor at one end attached to a motor speed controller so that it could rotate slowly. The speed controller (our PWM-OCX) was linked to a foot pedal switch made from some wood and a microswitch. This allowed for the rotation to be started and stopped easily while keeping hands free for holding the wire.

When winding the coil it should be kept clean and the wire must be kept tight so that no kinks occur. After winding it was coated with polyurethane varnish to protect it from physical damage and to reduce the risk of the arcs flashing over the windings.

Used to store energy and to provide a place for sparks to come from

Tesla Coil ToploadThe topload is made using two separate spheres. The larger one is an upturned metal dome used in Van De Graff generators while the smaller one is a ‘floating sphere’ from a local DIY store. The smaller sphere has had a brass pipe fitted through the center so that it can be connected to the coiled pipe mentioned earlier. This sphere is just placed on the larger one which gives easy access to the pipes when changing experiments.

Tesla Coil BreakoutThe size of the topload will have an effect on the resonant frequency of the Tesla Coil. With the topload as shown the secondary coil had a resonant frequency of around 435kHz. Removing the small sphere makes it 455kHz and having no topload makes it 570kHz

A larger topload will give the secondary coil a lower resonant frequency and will also make it harder for a spark to break out. This allows the arcs to be larger than they would be if no topload were present.

Sometimes if a large topload is needed to get the right resonant frequency, a small point such as a metal rod or screw can be placed somewhere pointing outwards. This is known as a breakout point and will cause the sparks to come out at the end of it. This occurs because the point will have a large electric field gradient compared to the smooth round surface elsewhere.

When we upped the power from 500kVA to 1kVA steamers came from all over the surface of the topload. In order to get them to come from one place and be larger, a breakout of about 20cm was used.

Control Box

The control box houses the two variac’s, a 120V transformer, a power relay, RFI filter, and a key operated switch.

The large variac is rated for 10A which is more than enough for the transformer used here. This variac allows a simple adjustment of the input voltage to the NST from 0V to 270V. The smaller variac is used to control the phase angle of the motor for the rotary spark gap. This allows for the timing of the capacitors discharge to be adjusted to match perfectly while the Tesla coil is operational.

Circuit Diagram

The diagram below shows the main tesla coil system components. The Terry filter is shown in simplified form in this diagram. The input to the circuit is 220V AV at 50Hz which is standard UK mains. This is first fed directly into an RFI Filter before then going to a large 10A Variac (T3). This variac allows the input voltage to the NST (T4) to be varied from 0 to 270V.

Tesla Coil SRSG Main Schematic

Only the RFI filter is connected to mains earth. The terry filter, NST, and secondary coil are connected to RF ground. The RF ground is made by forcing a large copper plated iron rod into the earth near the coil.

CT RT , MT, R1 and R2 are parts of the terry filter described earlier. In addition to this filter, a safety spark gap (G1) is used which will fire if the voltage is too high.

The main electrodes of the rotary spark gap ar. shown as G1 and connect to the main tank capacitor (C3) and the primary coil.

Tesla Coil SRSG Gap SchematicThis diagram shows how the motor is wired to a variac for electronic phase control. This really makes things a lot easier to get the coil running well. A small variac (T1) passes power to the synchronous motor. The inductance of the variac combined with the capacitance C1 will allow small adjustments in phase of the synchronous motor. It is necessary to turn the variac to maximum to start the motor and allow it to lock on to mains frequency. It can then be turned back about 1/4 of a turn to adjust phase by about 25 degrees before the motor looses lock.


The video below shows our first attempt at launching a rocket from the topload of the Tesla coil while it is running. The video is not great as we were a little afraid!

Tesla Coil SRSG Rocket1 SparksTo launch the rocket, a remote trigger for igniting the fuse was needed. This was made by using a home made air operated switch that connects a 12V battery to a 10 ohm resistor. The resistor heats up quickly and ignites the rockets fuse. The battery, switch, and resistor must all be contained within the topload sphere as they will be protected from the high frequency, high voltage. The airline passes down the inside of the secondary and out to a large syringe near the control box. When the syringe is pressed, the switch activates and the rocket launches.

So far we have only had one try at this as we can only do it when the weather is good. It is quite difficult to get a get photo of the rocket as it exits at high speed. We will need to do this experiment several times to get some god shots. In the photo above there is a large foil lined tube which contains the rocket. You can see as the rocket starts, the flames are leaking in various places. We will need to make a special topload for doing this again as to avoid damaging the coil.

DIY Kirlian Photos

Kirlian £2 coinA kirlian photo is a photograph of electrical corona produced around objects under the influence of high voltages.

There are two common methods for producing kirlian photos. One is a little tricky, but the other method is quite simple if you have access to a few basic bits of equipment. You can see how to make a high voltage power supply supply on the DIY ignition coil driver page and others. If you are less familiar with building electronic circuits you can use our power pulse modulator to drive a hv spark coil as a high voltage source. The electrode plate can be made yourself or the easiest way is to use ITO coated glass.

We have a selection of specially made transparent electrodes for use as Kirlian Photo Plates which work great in this project.

high voltage danger logo

Kirlian Photo Components

This method allows you to photograph or view electric field around object wit the naked eye. It works by creating a high voltage field between an object and a transparent electrode. The high voltage field causes ionisation of the air which is visible as a purple glow known as corona. The image above shows one of our Plasma Photo Plates resting on some high voltage insulators. You can use any insulator such as some plastic cups or glasses. Our electrode plates are provided with a filling syringe and caps so that it is easy to get started. Connected to the electrode plate is a high voltage spark coil which is being driven by our Power Pulse Modulator. The Power pulse modulator (PWM-OCXi) allows the high voltage coil to be driven with a variable frequency and power levels. This allows for different effects to be produced. At high frequencies, the plasma (or “aura”) tends to be softer and gives a smooth glow over most of the objects surface. At low frequencies the plasma tends to be longer and more jagged like lightning. It also tends to come mostly from the edges of the object rather than its surface.

Filling the Electrode Plates

First of all, the electrode plate must be filled with an electrically conductive solution. This is simply made by dissolving salt into ordinary tap water. You should add as much salt as will dissolve without making the water cloudy. Its is best to prepare the solution an hour before so that it has time to dissolve fully.

Kirlian Photo Place Filling Electrode

Connect the pipe to the end of the syringe provided and then draw some salt water into the syringe. (The amount needed will depend upon which size electrodes you have) Carefully put the other end of the pipe over one of the small plastic tubes on the edge of the electrode, tilt it as shown in the image and then slowly inject the solution into it. Make sure you go slowly to prevent leaks. Fill until a little solution comes out of the other plastic pipe, and then seal this with one of the caps. Remove the pipe and syringe and replace with the other cap. Wipe the electrode with a damp cloth and then make sure it is thoroughly dry and clean.

Attaching a sample

Take your sample such as a leaf or coin and tape it to the surface of the electrode as shown below.

Kirlian Photo Place Sticking Leaf

Tape a piece of wire to the back of the sample and connect the other end of this wire to ground. The ground connection should be the same as the ground or earth connection of your power supply. Turn the electrode over so that the sample sits underneath and place it on top of some insulators. You can use any non conductive object such as plastic cups or glasses. Connect the High voltage coil (or other HV power supply) to the metal connector on the electrode either directly as shown, or using a wire.

Connect all the other wires up so that it is ready to run. Familiarize your self with the layout as you will need to know where things are when you switch off the lights.

Kirlian Photo Plate Setup

Info Symbol Red

Taking the shots

Turn the lights off and give your self a moment for your eyes to adjust to the darkness. Turn on the power and tune it to give the best possible image.

Kirlian Photo Plate Setup On

You should only have the power on for several seconds at a time. If it is on too long the sample could be burned or the high voltage could etch marks into the glass. Also if used at high power, the PWM-OCXI and coil will get hot so they will need to be allowed to cool. We recommend adding a push switch so that you just hold your finger on it to activate the device while taking a photo. You will need a camera with a good lens or high ISO setting so that it can take good pictures in the dark. Using different settings such as shutter time will allow you to get different quality photos.

Hourglass Blue

You can also try an alternative setup using two or more electrode plates together as shown below. This allows you to add samples without having to stick them down or attach wires to them. It also allows for a wider range of effects.

Using Two Electrodes

Kirlian Photo Plates 2 Plates

Here you can see one large plate at the bottom and a medium sized one on top. You can use any sized plates combined together but larger plate will need more power. The sample is placed between the two plates and the ground connection is made to the second plate. You can try having the grounded plate on top of the HV plate or visa-versa for different results.

Kirlian Photos using Photographic paper of Film

This alternative method uses photographic plates or paper which can be expensive and hard to find. It can also be tricky to do correctly. The advantage though is that you can sometimes get images with various colours showing. The sample such as a leaf is placed directly onto the photographic plate. When exposed to high voltage the corona will effect the photosensitive chemicals in the photographic plate in different ways depending upon the intensity of the discharge.

Kirlian Diagram1

This diagram shows how the sample to be photographed is placed on top of the photosensitive paper with an insulated metal plate below. The lower plate is connected to a high voltage source of several kV. While the sample is usually grounded for brighter results.

Obviously all this setup must be kept in the dark as to avoid exposing the photo paper to light. The power is usually switched on for around 30 seconds to get a good enough image.

Kirlian2If you don’t have photographic paper you could use the film from a polaroid camera. Polaroid cameras will eject a protective layer of card when you first insert a film. You can use this feature to develop your exposed film.

To make a kirlian photograph using polaroid film you should remove one film from the cartridge and expose your sample just as described above. After you have exposed the film, carefully place it back inside the film cartridge in the top position. Load the cartridge back into the polaroid camera and it will immediately eject the top film. When the film is ejected it passes between a pair of rollers which spread the developing chemicals over the image so that it is fixed and now safe to expose to the light.

Myths and Pseudoscience

Kirlian1Many people claim that this sort of photo is showing the “life force” or “aura” of living things. This is something many pseudoscientists are using as so they can sell you these sorts of cameras for thousands of dollars. This page should hopefully show you how simple they actually are and that it is just simple corona and ionisation effects that are being observed.

There are also claims of a “Phantom Leaf” experiment where a kirlian photo of a leaf with a piece cut away showed an image of the full leaf. Proponents of this idea claim that this “proves” that the “Life Force” lingers on after the original piece of leaf is removed.

The only legitimate reasons for any phantom images would be caused by water or etching on the surface of the glass plates of the equipment. Any claims of anything else are totally unfounded and such people should not be taken seriously. If you try moving the cut leaf to a different camera, or use new clean glass plates then no “phantom” effect is observed.

You can even take kirlian images of things like your finger tips or whole palm. There are people who claim that you can diagnose illness from the shape of the images produced. This is really outlandish any many people are taken in by these scammers. There are charts that even relate each finger tip image to a certain part of the body or emotional states. These claims are just pure fantasy, and are another method used to make money selling expensive cameras.

Some of these sites often use scientific terminology in all sorts of inaccurate ways and even list quotes of support from people who are apparently Doctors or experts in something. The fact is that there is no legitimate reproducible experiment that gives evidence to support any such claims.

Example Kirlian Photos

Kirlian Photo Plate Coin2 plate

This kirlian photo shows a £2 coin between two of the electrode plates. The surrounding dots are caused by tiny amounts dust and dirt on the glass surface.


Kirlian Photo Plate Coin Waves

This kirlian photo shows a close view of the same coin and with a higher frequency supply. You can see rings or waves around the coin.

Kirlian Photo Plate Coin Waves B

Another shot of the waves around the coin

Kirlian Photo Plate Dust 2plate

This is a photo taken when no sample is placed between the plates. All the little dots are probably dust although we had tried to clean the surface thoroughly.

Some of these dots would move around the electrodes due to electrostatic effects.

Kirlian Photo Plate Dustbright 2plate

Same image with longer exposure time on camera.

Kirlian Photo Leaf 1plate

This is a photo of the leaf shown in the instructions above

By adjusting the frequency while watching it, you can see the glowing corona move around different parts of the leaf.

Another leaf image at high frequency.

Kirlian Photo Magnets 2plate

Three Neodymium Magnets between the electrode plates.

Kirlian Photo Plate Magnet Waves

A single Neodymium magnet

Kirlian Photo Plate Magnet s waves

A bunch of little magnets. Notice the rings or waves again

Kirlian Photo Plate Queen

The £2 coin at low frequency under a single electrode.


More Photos

You can see more Kirlian photos and high voltage plasmas on the Plasma Page

Neon Gas and Tesla Coil

DIY Mini Tesla Coil

A DIY Mini Tesla Coil

DC Powered with Plasma Output

The aim of this design was to get the highest voltage (or longest arcs) possible from a single self contained unit.

high voltage danger logo

This coil operates from 12V or 24V SLA batteries. A pair of car ignition coils are used to provide around 20kV for charging the capacitor bank. The ignition coils are driven by a variable frequency square wave from a 555 timing chip and four large transistors (2N3055).

Battery Powered Tesla Coil Input Voltage 12 – 24V DC
Power Consumption 250W Max
Max Arc Length 25cm
Output Voltage(approx) 250kV
Primary Transformer 2 x Car ignition coils in parallel – 20kV
Capacitor MMC 20 kV
Spark Gap 5 x 6mm pipes, Variable
Primary Turns 850
Secondary Turns 850
Secondary Height 40cm
Secondary Width 5cm
Topload 10cm Sphere
Special Features Plasma/Flame discharge terminal Battery powered Fully portable Variable coupling Basic power Management

A pipe from a hole in the top of the sphere and down the inside of the secondary coil is used to supply gas to form a type of plasma electrode.

Flame from coil discharge terminalUsing Butane gas and air, a blue flame can be used as an interesting discharge terminal. The heated CO2emissions provide a low pressure channel to conduct the electricity more easily than air. This produces a large plasma column above the flame. At certain spark gap discharge rates the plasma column can be made to resemble a stable double helix formation. Small quantities of other gasses such as neon or helium can be mixed with the butane to produce slightly different colours and effects. The table below should help you find some of the components needed for this project.

Spring on Tesla Coil thumbnail

Component Max Voltage Source
Ignition Coils ~20kV Click Here
Capacitor Bank 20kV Click Here
HV Diode 30kV Click Here
Power Transistor 400V Click Here
Neon / Helium n/a ST Gas
Control Circuit n/a Click Here

More Plasma Photos

Capacitor BankCapacitor Bank – The capacitor used in this project was made by combining a large number of lower valued capacitors. By connecting smaller capacitors in series the overall voltage they will tolerate is increased. To obtain a higher storage capacity (capacitance) the capacitors can be connected in parallel. This type of capacitor bank is known as an MMC (Multi Mini Capacitors). The next version of this project will use specially designed large pulse discharge capacitors. These capacitors can be more efficient than an MMC, but they can be expensive and hard to find.

Ignition CoilPrimary Transformer – Ignition coils (Induction coils) obtained from a scrap yard are used for this design. The old ignition coils provide a very cheap way of generating a high voltage for charging the capacitor. The voltage increase in an ignition coil is not determined by the turns ratio like in normal transformers. The secondary voltage depends upon the rate of change of the current in the primary coil. Older ignition coils such as ones from a scrap yard may not work as well as new ones. Over time the insulating oil inside the casing becomes less effective and can lead to internal arcing. This can damage the transistors and the control circuit, rendering them useless

Power Transistors on heat sinkControl Circuit – The control circuit is based on a simple oscillator provided by an NE555 timer chip. The square wave pulses are sent to a set of four 2N3055 power transistors mounted on a large heat sink. These transistors can switch a good amount of power quite quickly, but they can be sensitive to voltage spikes caused by feedback in the circuit, or faulty ignition coils. The Ignition coil driver circuit shown below shows how the signal from the 555 chip is pre-amplified, so that the large transistor array can be driven effectively. Using 2N3055 transistors in this way is not ideal, but it is what we had available at the time for the project. Modern IGBT transistors are much more effective and less
prone to failure from voltage spikes.Ignition Coil Driver Circuit Diagram

The output from the ignition coils is rectified (converted to DC using diodes) so that it can charge the capacitor bank C1 shown below.

Rectifier Schematic

Primary CoilCoils – The primary coil is simply made from 2mm enameled copper wire, wound around a plastic stand. There are six turns in total, but the connection is made at about 4.5 turns when tuned. The secondary coil is wound from 0.4mm enameled copper wire around a plastic drainage pipe.

Safety – Attached to the capacitor is a short circuit switch that is activated by a long plastic handle. This is used to make sure the capacitor is fully discharged, and cannot recharge whilst making any manual adjustments. There is also a switch to isolate power from the ignition coils that is activated using a insulating pull cord.

Hole in topload sphereSpecial Features – This project has several extra features compared to a common Tesla Coil. The topload sphere has a small hole to allow gas to be emitted. A 5mm plastic pipe runs down the inside of the secondary coil, and out of the plastic base.

Plasma and Arc Photos

This allows the gas to be piped in, without interfering with the normal operation of the Tesla Coil.

Neon Helium GasFuture Developments – This project is currently being upgraded. The new design aims to achieve a higher power throughput. By using more ignition coils in parallel it should be possible to increase the size of the spark gap, or to fire it more rapidly. New ignition coils will used instead of the second hand ones for improved stability. The new design also incorporates voltage and power monitoring features. It also has a neat metal finish and multiple outputs so that it can be used as a multi purpose portable high voltage power supply

Click here to see the new project

DIY Plasma Globe

DIY Plasma GlobeThere are all sorts of ways to make a plasma globe. This page deals will detail how to make one using a small amount of easily obtainable components. A normal transparent light bulb can be used as a plasma globe simply by connecting it to a high voltage, high frequency source. Most light bulbs contain low pressure Argon gas to prevent the hot filaments from burning. Fortunately this arrangement is also ideal for making contained arcs of plasma. The power supply required for the plasma globe would preferably be a high voltage, high frequency AC type, which could be made from an ignition coil, like the ones used in the Homemade Tesla Coil project. The schematic below shows a driver circuit, for more details see the Ignition Coil Driver page. We also sell a ready made ignition coil driver (shown in the pictures) which also includes extra features.

hv danger logo WARNING: High Voltage Devices!

Ignition Coil Driver circuit diagram

Assembling the Plasma Globe

Parts needed to construct a plasma globeThe following parts are used for the video demo of this project;

First the spring must be attached to the bottom of the light bulb; this can be done using a bit of tape. The spring is used to ensure a connection between the bottom of the bulb and the high voltage output within the end of the ignition coil. Next, the bulb and spring are fixed tot he end of the ignition coil with some more tape.

The ignition coil is connected by two wires to the PWM circuit at the L+ and L- terminals, and the power supply is connected to GND and V+. Also connected to V+ and GND is the electrolytic capacitor. This is connected close to the circuit board and is used to keep the DC input stable. It is important to note that the orientation of the capacitor must be correct. To know which way around it should go look for the longer leg (which indicates the positive) there is also often a stripe on the side of the capacitor to indicate the negative side.

Finger of PlasmaThe settings on the PWM circuit will need to be adjusted so that good streamers become visable in the coil. Always begin with the duty setting at zero then slowly turn it up to around 50%. The frequency setting is then adjusted while observing the apperance of the plasma inside the lightbulb. At some frequencies no plasma will be seen, while when at the right frequency there should be lots of streamers dancing around inside the bulb. The frequency needs to be fairly high and the buzzing sound from the coil will become so high its is amost inaudiable.

When operating the circuit great care must be taken as the ignition coil could output around 20-30kv when using around 15V, 5A from the power supply.It should not be touched as it will give a nasty shock.

HHO Electrodes

DIY HHO Hydrogen Production a Water Fuel Cell

DIY HHO Hydrogen Production a Water Fuel Cell

DANGER: This project involves creating a mixture of Hydrogen and Oxygen which is a highly EXPLOSIVE GAS. When contained in a confined space, detonation of the gas would be highly dangerous and could cause serious injury.

How it works
Water is a compound made from the two elements of Hydrogen and Oxygen. It has the chemical symbol H2O which indicates that each molecule is a combination of one Oxygen atom and two Hydrogen atoms.

All atoms can form ‘ions’. These are just the same atom except with a little extra charge. Atoms can become ionized when in the presence an electric field. You can see extreme examples of this in the DIY Tesla Coil project. Hydrogen forms positive ions, and oxygen forms negative ions. We use this to our advantage by using an electric field to pull the water molecules apart.

By placing two electrodes (metal plates) into water we can create an electric field between them by connecting them to the terminals of a battery or power supply. The positive electrode is known as the anode, while the negative one is the cathode. Pure water actually does not conduct electricity so it is not suitable to be used without adding something to the water. Tap water already contains many dissolved compounds which allow the water to conduct. The ions formed in the water will be attracted to the electrode of opposite polarity, i.e. the positive hydrogen ions will move towards the cathode, while the negative oxygen ions move to the anode. Once the ions reach the surface of the electrodes the charges will be neutralised by adding or removing electrons. The gas is then fee to bubble up out of the remaining water to be collected.

The electrodes are typically made from metal or graphite (carbon) so that they can pass electricity into the water. It is important that the chosen material does not react readily with oxygen or one of the dissolved compounds otherwise reactions will occur at the surface of the cathode (negative electrode) and the water will become polluted with the products of the reactions. You will see an example of this below when copper electrodes are used. This also means that no or very little oxygen gas is released as it gets combined with the metal electrode and remains in the container.

Copper ElectrodesThe Project

This is a simple project that is used to create Hydrogen and Oxygen gas by electrolysis of water. The aim was to get good gas production rates without using extra chemicals or eroding the electrodes.

The first electrodes tried were ones left over from a different project. They were made from Copper coated Carbon rods which are not ideal due to copper being able to react with the water. The idea was that the copper would eventually all react away and there would be just Carbon left which would not pollute the water.

The copper seemed to take too long to react away and it was decided that this would not be useful at all. Below you can see the result of using copper electrode for electrolysis. The blue sludge floating on the surface of the water is some reactant of the copper and tap water.

Blue Copper

Many people use electrodes made from stainless steel kitchen ware or switch plates because the stainless steel does not react as easily. The problem is that the grade of the steel often found in such items is not great and you will be left with a brown sludge after a few minuets of operation. They are also quite thin, usually less than 1mm, which means that the do not last a very long time before being totally eroded away. The erosion of the electrodes happens much more quickly when high currents or solutes (often called catalysts) are used.

The volume of gas produced is proportional to the charge passing through the water (current) and therefore high current means more gas. To do this the spacing of the electrodes must be as close as possible while still having enough room for the gas to bubble out freely.

The metal chosen for the plates was special high grade stainless steel to reduce corrosion. Such metal is not as conductive as others like copper for instance, so these plates were made from thick sheets of 2mm to counter this potential limiting factor. Very high quality metal was used which meant it was too hard to cut with common DIY tools so these plates were cut using a high pressure water jet. 

 INFORMATION: Even the highest grade stainless steel will have some reaction with water and can produce toxic chemicals. Avoid touching the water after use.

HHO Electrodes

The plates are layered on top of each other with nylon washers between used as spacing. They are placed in alternating positions so that the plates would be +-+-+-. Stainless steel fixings were then used to fit it all together. It is important that it is put together well otherwise sparks could occur in the gas production area resulting in an explosion.

ElectrodesA total of 16 plates were used in with 1mm spacing between each of them. The large combined surface area and thickness of the plates and bolts meant that this could carry very large currents without significant resistive heating in the metal. The total capacitance of the electrodes was 1nF when measured in air which indicates a large close surface area for gas production. This set of electrodes would draw about 25A from ordinary tap water. To collect the gas, the electrodes need to be placed in some sort of container. The container used was just something from a supermarket and was originally intended for storing something like tea!

This video shows the result of applying 12V to the electrodes when submerged in ordinary tap water. No ‘catalysts’ have been added to the water at all, this is just tap water!

It is drawing about 25A. Power to the cell is controlled using a pulse width modulation circuit.

The container was made from metal so it was important to place the electrodes on a plastic base to prevent any short circuits. This image shows how two banana sockets were installed either side of some copper and brass fittings used to extract the gas. The power and pipe fittings were screwed tightly and sealed with silicon sealant so that the closed container would be air tight.

The gas produced is a highly explosive mixture of Hydrogen and Oxygen and should be treated with extreme caution. A large volume of gas exists inside the container which if ignited would explode and destroy the container. To avoid detonating the gas, the pipe from the container is fed into the base of another container which is half filled with water. This allows the gas to bubble trough the water to then be collected via another pipe which is used as the gas output. Now if any ignition occurs at the output, the flames can’t get back past the bubbler device and into the large gas volume in the electrolysis cell. This is an absolutely essential safety device and should not be skipped.

Now it is just deciding what to do with the gas! A good way to see the how explosive the gas mixture is to bubble the gas through another container of water such as a mug and ignite the bubbles as they reach the surface. Each bubble will explode very loudly and probably blow out the lighter.

A similar project which uses the explosive properties of the gas is the Hydrogen Cannon experiment.

 You should be aware that detonating this HHO gas mixture is VERY VERY loud.

Spark coil uses

You probably wouldn’t realize but you use spark coils all the time whether you’re cooking a meal or driving a car, spark coils are everywhere and their applications are countless. I will list a few.

If you’d like to try these things for yourself then be warned, spark coils are high voltage and should only be used by those who know what they’re doing, if you do know what you’re doing then you can buy spark coils here on the RMCybernetics shop.



An electric arc or arc discharge is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current through normally non-conductive media such as air.


An electrical discharge results from the creation of a conducting path between    two points of different electrical potential in the medium in which the points are immersed. If the supply of electrical charge is continuous, the discharge is permanent, but otherwise it is temporary, and serves to equalize the potentials. Usually, the medium is a gas, often the atmosphere, and the potential difference is a large one, from a few hundred volts to millions of volts. If the two points are separated by a vacuum, there can be no discharge.

An spark coil can be used to make arcs by putting a high voltage through it and putting it close to ground.



DIY Plasma globes :

untitled-3A glass globe containing a low density gas and a central electrode that creates lightning-like streams of light. These fronds of plasma make their way from the centre of the globe to the edge, in a bid to reach earth. Creating an enhanced path to earth by touching the globe increases the strength of the discharge, which is why the arcs are attracted to your hand if you touch the globe.




Jacobs ladder:

jacobs-ladderThe Jacob’s ladder is a high voltage climbing arc. An electric spark jumps between two parallel wires. The spjacobs-ladder-2ark then “climbs” up the ladder. The transformer at the bottom creates a potential difference between the wires. The electrons repel each other, so they jump from one wire to try and get as far apart as possible. The spark heats up the surrounding air and hot air rises, so the spark rises with it. When the spark gets to the top of the wires, it dies and a new one starts at the bottom.




DIY Fly swatter/Bug trap:

diy-fly-swatter-bug-trapThis can be made using a high current through a set of parallel wires and set of parallel grounded wires running horizontally/vertically (whichever way the high current wires aren’t).

The high voltage supplied by the coil, at least 2,000 V, is applied across the two wire-mesh grids. These grids are separated by a tiny gap, about the size of a typical insect (a couple of millimetres). The light inside the wire-mesh network lures the insects to the device (many insects see ultraviolet light better than visible light, and are more attracted to it, because the flower patterns that attract insects are revealed in ultraviolet light). As the bug flies toward the light, it penetrates the space between the wire-mesh grids and completes the electric circuit. High-v­oltage electric current flows through the insect and vaporizes it.



taserA Taser or Thomas A. Swift’s Electric Rifle is a device that fires electrified probes used to temporarily incapacitate someone.

A Taser works by delivering high voltage — but low amperage — to the human body. A Taser delivers a powerful but temporary shock rather than a sustained and deadly charge.


Electric fence

electric-fenceThe most common use for an electric fence is to contain animals in a certain space by deterring them (often using mild shocks) from crossing a boundary. While possible to be run from an spark coil in a DIY situation it is highly recommended NOT to as it can be very dangerous.






An spark coil (also called an ignition coil) is an induction coil in an automobile’s ignition system which transforms the battery’s low voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel therefore ignition is its primary function.

Feel free to list a few ideas you think I should have mentioned in the comments section.