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Induction Heating

Guide to Induction Heating

This page will discuss the practical side of induction heating to help you understand how to make use of it and how to optimise your system. Induction heating is a method of non-contact heating using high frequency electromagnetic fields. Induction heating only works on electrically conductive materials and the efficiency at which electrical power is converted to heat will vary significantly with different materials.

Heating a Steel Nut Red HotAn induction heater heating a steel nut red hot

How does induction heating work?

The heating effect works by inducing a current to flow in a material by exposing it to an alternating magnetic field. This alternating magnetic field is typically in the kHz range and is created using a resonating coil.

When the induced electrical current flows in a material, heat is generated through resistance losses and also hysteresis losses in ferromagnetic materials like iron. Typically, the easiest materials to heat will be of relatively high resistance (but still a conductor), and be ferromagnetic like iron. Low resistance materials like copper and silver can be very hard to heat with induction. When melting silver, for example, it is usually best to heat a graphite crucible and place the sliver inside. This is because graphite is easy to heat with induction and it will then heat the silver indirectly.

One advantage of induction heating is that only the metal parts will be heated and you could, for example, heat a metal part that is totally sealed within a glass container without directly heating the container its self. Other advantages of induction heating include safety (flameless heating), precision, and efficiency.

Working with our induction heater systems

We offer a range of induction heating components for sale which can be used to create a wide range of projects and experiments. Below you will find information to help you get the most out of these and to help you to understand your induction system. We also offer custom electronics design services and consultancy for if you need help making a specific project.

Micro Induction Heater Circuit

Induction Heater Circuit
Induction Heater Circuit

Transferring Heating Power from the PSU to the Workpiece

In order to deliver maximum power to a work coil, they are driven at their resonant frequency. Doing this minimises power loss in the driving circuitry and maximises efficiency. The work coil also has a parallel capacitor which forms the other part of an LC resonant tank circuit. Some induction heater systems use a series resonant capacitor and coil, but in this article we will discuss the parallel resonant systems. When being driven at its resonant frequency, energy builds up in this LC tank leading to very high currents. This means that although you may be drawing, for example, 10A from your power supply, there could be 30A or more flowing back and forth between the capacitor and work coil at very high frequency. Because of this, it is important to consider those currents when designing a work coil for your induction heater system.

Simplified Induction Heater Diagram

Figure 1: Simplified Induction Heater

It is also important to consider how adding a piece of material into the work coil will alter the amount of power drawn by the system. When the coil is resonating without any workpiece, the current draw from the PSU will be relatively low, but once something is added, it can rise significantly. How much it rises will depend on the total mass, the material from which the workpiece is made, and how close the windings are to the material. For example; in one of our CT-400 coils running from a 15V supply and a driver circuit (such as our CRO-SM2), the current draw could be about 3.5A from the PSU when nothing is in the coil. If we add something like an M6 steel bolt, the current draw will rise to over 10A. Yet if we inserted an M6 stainless steel bolt, the current draw would only rise to around 5A. There would also only be a small change when adding a material like copper. More about the effects of different materials is discussed later.

Also affecting the rise in current when adding a workpiece is the magnetic coupling. A large coil and a small workpiece will show only a relatively small rise in current, whereas a small coil surrounding the same workpiece would allow the current to increase significantly. When adding ferrous materials like Iron, the magnetic coupling is increased and this makes them much easier to heat. However, when such materials reach a high temperature, they will lose their magnetic properties due to something called the Curie Effect. At this point you may see the PSU current drop, and it will become more difficult to increase the temperature further.

The rise in current from the PSU when adding a workpiece to the coil is an excellent indicator of how effective the heating will be. It is therefore important to balance all these factors when considering a coil design for a particular induction heating project.

Another important consideration is parasitic elements in your circuit. These are small elements of inductance, resistance and capacitance that are not deliberately chosen to be there, but are a product of the physical nature of components (such as the connecting wires). Since these parasitic elements can cause losses and interference, it is important to reduce or control these as much as possible. A simple parasitic element would be the resistance of the metal in the wire or pipe used to make a work coil. This resistance will cause the coil its self to heat up when current flows in it so it is important to minimise this loss by using thick, high-quality wire. Another issue to consider is the skin effect. This is a phenomenon where high frequency currents tend to flow mainly on the outer surface of a conductor. This means that if using ordinary wire to make a work coil, a large amount of the conducting copper is never actually used and it therefore has a higher parasitic resistance. The skin effect can be minimised by using specialist cable known as Litz Wire. This has multiple insulated strands of wire twisted together to prevent the current being pushed to the outer surface. You can find Litz wire for sale in our shop. Sometimes it is not practical to use Litz Wire so it is common to use copper pipe as water can be pumped through it to keep it cool. This is typically the best method when heating things red hot as the radiated heat from the workpiece would melt the insulation in a litz wire.

The parasitic resistance in a work coil will cause the coil to heat up, waste power, or even overheat and melt. Another effect the resistance has is to reduce the Q factor of the resonant tank. This is important as the current resonating in the tank is roughly the input current multiplied by the Q factor. The parallel capacitors also have some parasitic resistance so it is important to choose ones that not only have a low resistance (known as ESR), but also capable of handling high currents at high frequencies. A common method of minimising parasitic ESR is to use an array of smaller capacitors connected in parallel so that the current is shared between them and the resistance is reduced overall. We have a range of suitable induction heater capacitors for sale in our shop.

Parasitic Resistance

Figure 2: Parasitic Resistance in an Induction Heater

Another important parasitic element is inductance. Any current carrying conductor will have some inductance which causes a resistance to change in the current flowing in the circuit. In an induction heater, this can both be useful, and harmful, depending where in the circuit the inductance is.

The LC tank circuit has a specific resonant frequency at which we drive it for maximum efficiency. However, other small inductances and capacitances in the connecting wires also have natural resonant frequencies that may differ from that of the LC tank. This can create harmonic frequencies which trick the driver circuit in to oscillating at the wrong frequency, or a mixture of several frequencies.

A ZVS driver like our CRO-SM3 and CRO-2 can be vulnerable to latching onto parasitic oscillations, so it is important that the layout and connections between the work coil, tank capacitor, and driver circuit are made carefully.

Long leads between the driver circuit and the LC tank will create significant parasitic inductances. Consider that a typical work coil like our CT-400 may only have 100cm of copper pipe making up the whole coil. If you have 25cm connecting wires between the CT-400 and the driver circuit, this adds another 50cm of conductor with an inductance of its own. This inductance is not part of the LC tank as it is before the tank capacitor so any resonance from it will be detrimental to the system.

Parasitic Inductance

Figure 3: Parasitic Inductance in an induction heater

If we move the tank capacitor to the other side so it sits between the connecting wires and work coil, the problems with mixed frequency resonances will be mostly eliminated as the inductance of the wires now basically forms part of the work coil. However, this means that those connecting wires will also carry the same high currents as the work coil and will heat up if they are not suitably large. In a water-cooled coil this can be quite impractical to do.

It is possible to mitigate some of the parasitic resonance by adding more tank capacitance at the output terminals of the driver circuit, between the circuit and the connecting wires. This can reduce the high frequency ringing cause by the leads and help the driver to lock on to the correct frequency.

Split Tank Capacitor

Figure 4: Split Tank Capacitor to compensate for long leads

There are also parasitic inductances and capacitances in the driver electronics themselves. These can be much harder to deal with as they are mostly just part of the physical nature of the components. These parasitic elements become much more significant when driving very high frequency coils, and much less so at low frequencies.

In all cases it is necessary to make trade-offs in the system design based on what is practical, the power requirements, target frequency, efficiency, and cost. If you need any help working out what is the best way to approach your system design, please get in touch.

Induction Heater Coil Design Tips

The work coil design is critical for achieving maximum performance in any induction heating project. While a simple work coil like our CT-400 will suit a range of applications, if you want to make use of every watt, then the work coil must be designed to suit your project.

There are a few fundamental work coil shapes commonly used in induction heating. Their shape is chosen to maximise coupling and power transfer to the workpiece as well as being practical to use.

The first thing you should consider when looking at an induction heating project is the power requirements. To heat a known mass of material in a known time is relatively easy to calculate. You can use our handy heater power calculator to get a rough idea. When using this you should consider the efficiency of the power transfer from PSU to heat in the workpiece, and also the heat lost as IR radiation. A hot metal part will be radiating a large amount of heat into the atmosphere if it is not insulated. If we are melting jewellery in a graphite crucible, the entire thing can be insulated making for a very efficient process. If we are heating stainless steel in open air, then we not only have the low power coupling, but also the radiated losses to consider.

Custom Helical Coil Custom Pancake Coil

Helical Induction Coils
A typical cylindrical shape coil that creates a heating field within the inside of the cylinder. These are easy to make and will transfer power efficiently to materials within.

Pancake Induction Coils
Commonly used in induction cookers as they offer good coupling to the base of the saucepan. To be effective, the workpiece (like a saucepan) must be very close to the coil.

U-Shaped Induction Coils
These are basically a pancake coil that has been folded over. They are common for induction hardening of blades as it is easy to pass the blade through the coil while limiting the heating to only the edge.

There are many other sorts of induction coil shapes, often custom made just for one specific application. Please feel free to get in touch or post a message below if you want to discuss a custom induction heater coil design.

The work coils job is to transfer power from the system PSU to the workpiece (material being heated). Generally speaking, we look at the combined coil and workpiece as a single transformer with the work coil being the primary coil, and the workpiece being a secondary coil (consisting of just one turn). We can use this approximation when making calculations as the current flowing in the secondary coil of a transformer is proportional to the current in the primary coil multiplied by the number of turns. While this sounds simple, it can be more complex in practice as we also must consider the resistivity of the workpiece and the electrical impedance of the work coil.

In a typical helical (cylindrical) coil the magnetic flux density is not homogenous throughout its volume. Most of the flux is concentrated near the outer edges of the volume within the coil. This means that if placing a small part in a large coil, it will absorb more power if placed within the inside edges rather than in the centre of the coil. There is also a lower flux density at each end of the coil. When the workpiece is made from a ferrous material, it will actually change the way the lines of magnetic flux form within the coil, dragging them into itself and improving coupling. If heating something made from multiple materials, this effect should be considered as the flux may be diverted into or away from the other materials.

Induction Heating Different Materials

Which material works best for induction heating? The material a workpiece is made from will significantly affect its ability to rise in temperature within a high frequency magnetic field. Here we will compare a few materials and discuss how we can optimise our system to get the greatest heating effect. Iron typically works best in an induction heater with a power transfer of more than 90%. Copper on the other hand, will only make use of around 15% of power in the system. We typically think of metals being heated with induction, but other materials that can be heated too as long as they are significantly electrically conductive, but also have some resistance.

The main factors influencing the heating efficiency are magnetic coupling and resistivity. While heating due to resistance losses is proportional to I2R, this does not always translate directly in an induction heater system. For example, copper has a low resistivity and could therefore have a high current flowing within the material. However, the impedance of the driver limits power that can be delivered, while to current flowing in the copper will create a back emf in the work coil, also limiting the input power.  

An important factor to consider when heating larger volumes, is the thermal conductivity of the material. As high frequency induction heating only heats the outer surface directly (due to the skin effect), the remaining mass of material is heated mainly by the internal conduction of heat from the surface. In larger induction furnaces, lower frequencies are used so that there is deeper penetration of the heating currents.

Below you can find a table of a few common materials and some of the relevant properties that may be considered when used in induction heating.

Material Resistivity ρ (μΩ•m) at 20 °C Relative Permeability μ / μ0 Heat Capacity (J/g C°) Density g/cm3 Thermal Conductivity W/(m K)
Iron 0.1 5000 0.449 7.85 80
Stainless Steel (316) 0.74 1.004 0.502 8 16.3
Stainless Steel (304) 0.72 1.6 0.5 7.982 16.2
Nickel 0.0699 325 0.461 8.902 92
Tungsten 0.056 1 0.132 19.45 174
Copper 0.0168 0.999 0.385 8.96 386
Cobalt 0.056 60 0.435 8.9 69
Titanium 0.42 1 0.523 4.52 17
Graphite 3.75 0.999 0.717 2.66 247
Brass 0.7 0.999 0.375 8.565 96
Gold 0.0244 0.999 0.129 19.32 310
Silver 0.0159 0.999 0.235 10.497 419
Aluminium 0.0282 1 0.897 2.705 239
Tin 0.109 1 0.218 7.26 67
Zinc 0.059 0.999 0.377 7.068 113
Lead 0.022 0.999 0.129 11.29 35

Table 1: Important parameters of materials when used in Induction heating

* Values can vary significantly depending upon the exact composition, crystal structure, orientation, frequency and temperature. Where a range of values was given in the source, the value here is the average.

Data in this table is collated from numerous sources including those found below:

Iron (Nickel & Cobalt too)

Iron is an excellent induction heating material for several reasons. Iron is a ferromagnetic material which basically means it is attracted to magnetic fields and thus pulls the magnetic field lines towards it creating a higher concentration within. This basically increases the magnetic induction field strength and creates a high level of magnetic coupling between the coil and workpiece. Good magnetic coupling means an efficient power transfer from the system to the workpiece being heated. Ferrous materials can be magnetised like the way you can magnetise a screwdriver tip by passing it by a magnet. In a high frequency induction field, the material is being magnetised in one polarity and then another, over and over. This creates further heating through hysteresis losses. However, once iron gets really hot, it will reach the Currie Point and these magnetic advantages disappear. After this it is the resistance losses that will be driving any further increase in temperature. Iron has a relatively high resistivity (it doesn’t conduct well compared to copper wires), and this increases with temperature. This high resistivity means that more heat is generated by the induced currents as the heat generated is proportional to I2R (current x current x resistance).

Stainless Steel

Stainless steel can be heated by induction, but compared to mild steel or iron, it has some significant disadvantages. Being only very slightly magnetic, there is a low amount of coupling between the coil and workpiece, so it is important that the work coil form is close to the shape of the part being heated. It does however have a high resistivity which also increases with temperature so this does help it to generate heat from induced currents.


Carbon is an interesting material for induction heating as it is a non-metal, yet can conduct electricity. It has a high resistivity compared to metals which actually helps in the heating process making it much easier to heat than stainless steel. Other forms of carbon such as graphite, graphene, and even diamonds can be heated with an induction heater. Carbon is much less dense than many metals and therefore the same volume of carbon would heat much more quickly than a metal part the same size. This low density is what makes it a lightweight material and means that it will take less energy to raise or lower its temperature for a given volume.

Graphite CruciblesGraphite crucibles used for induction heating

Tin & Tungsten

Tin and Tungsten have a high resistivity and will heat well in an induction heater field. Tungsten however is extremely dense and therefore has a large heat capacity. Being very dense, it has a small volume for a given mass which means within the same sized work coil, it will intersect fewer magnetic field lines than a material of lower density such as Tin.

Copper & Aluminium

Copper and Aluminium can be heated in an induction heater, but the efficiency of doing so is very low. As good conductors of electricity, their low resistivity means lower resistance losses from the induced currents. However, like other metals, the resistivity increases with temperature and heating becomes more efficient as it gets hotter.

Precious Metals (Gold and Silver)

Silver being the most conductive element is extremely hard to heat directly with an induction heater. To heat precious metals, it is usually best to place the metal within a graphite crucible so that the magnetic field heats the crucible, and this transfers the heat to the metals via conduction and IR radiation.

Other Non-metals

There are a number of non-metals that can be heated with induction. This can be semiconductors, ferrites, and other compounds.

Ferrite NanoparticlesFerrite Powders used for Induction Heating

Ferrites have multiple uses in induction heating. MnZn Ferrite can be used for magnetic shielding or to guide the path of magnetic flux. Others like NiZn ferrite can be mixed into materials and heated up like metal. NiZn nanoparticles can be absorbed by biological systems and then heated by external fields. This allows heat to be delivered inside certain cells, but without heating the whole lifeform.


Custom induction heater circuit

Interconnected PWM

Bipolar PWM with Arduino

Our popular power PWM control circuits use a single transistor to pulse all sorts of loads for power control. The pulses control current in one direction only which is fine for most PWM applications. However sometimes it is required to have a bi directional pulse for driving an AC load such as a transformer.

Ideally a dedicated H-bridge circuit would be used, but it is possible to approximate this using a pair of our PWM circuits being controlled with an Arduino.

Using our Arduino library NanoPWMac we can drive two circuits with a pulse that is equal in length, but with only one circuit active at a time.

Below you can see a simplified diagram of what is happening with a normal single transistor PWM circuit. The pulse signal basically switches power on/off to the load by making and breaking the path for current from the PSU through the load.

Our PWM modules can be linked directly in a master/slave arrangement (see datasheet) so that when one is on, the other is off and visa-versa. This can be used to drive a transformer with AC, but it only really works if you want a 50% duty cycle. This is because if you set the master PWM to 10%, the other one will be 90% therefore driving the transformer unequally and not allowing for proper power control.

To dive a coil with AC and adjustable duty, an Arduino can be connected to two PWM circuits as shown below. The coil must be centre tapped so that each PWM will pull current in opposite directions.

For simplicity the power connections are not shown in the diagram. To link the Arduino to the PWM modules, the SIG jumper is removed from both modules, and a connection from the Arduino pins 9 and 10 is made to the SIG pin marked with a stripe on the OCXi.

The example program in the nanoPWMac library will take a reading from potentiometers connected to A4 and A5 so that these pots can be used to vary frequency and duty independently.

With this setup you can now pulse both circuits in opposition with a waveform like shown below.

Litz Wire

Litz Wire

What is Litz Wire?

Litz wire is a type of cable formed by combining multiple strands of thin insulated wire together side by side. It is used to carry high frequency currents as the insulated strands each carry a portion of the current and prevent losses due to the skin effect. Litz wire is commonly found in radio frequency (RF) applications, and high frequency power circuits such as induction heaters and Tesla Coils.

The strands in litz wire are typically twisted together either as a single bunch, or as multiple bunches twisted to form a large cable. By twisting the wires together it helps to control the magnetic fields around the wires and keep the currents flowing evenly.

What is the skin effect?

She skin effect is a term given to the phenomenon of when high frequency currents tend to flow near the surface (or skin) of an electrical conductor. This occurs due to magnetic fields being induced in the conductor by the changing currents. The magnetic fields make it difficult for the currents to flow anywhere but the outer surface.
With the currents being forced to flow in just part of the conducting wire, the effective resistance of the wire is greater. The higher the frequency, the more loss in the wire due to this resistance.
By using this skin effect calculator, we can see that at a frequency of 1MHz, the effective skin depth is just 65μm (0.065mm), while at 1kHz, the effective depth is 2062μm (2mm) in a copper wire. 

How to make litz wire

Using common magnet wire it is possible to make your own litz wire by twisting it together in bunches. It is not practical for large numbers of strands but is doable for short lengths with a small number of individual wires.

The simplest way is to cut equal lengths of the required magnet wire and to clamp or tie all of one end together. The other ends can be put in the chuck of a hand drill which is used to twist them tightly together.

How to solder litz wire

It can be very difficult to solder litz wire as they can contain thousands of individually insulated strands. It is necessary to remove this insulation before soldering can take place. This can be done by first burning the end to be soldered and then cleaning of the burned insulation with wire wool. Doing this without breaking the fine strands or leaving some of them uncleaned can be quite challenging.

The best way is to use a hot solder bath as this can both burn off the insulation and add the solder. The solder bath must be quite hot and it works best if the litz wire is first dipped into flux to help the solder to stick.

Where can I buy litz wire?

We have a range of litz wire sizes for sale and offer soldering services for ready to use litz cable assemblies. If there is a specific size you need that we do not stock, we can custom make it to your requirements.

Lasers and Interference

Diffraction and Interference

Diffraction through a slitDiffraction is the phenomenon where waves can be bent around obstacles. When coherent light passes through a fine slit some of the rays are diffracted. The varying levels of diffraction cause part of the beam to interfere, thus producing an interference pattern.

Light from most sources is incoherent. This means that the many waves coming from the source do not line up with each other, or are not in phase. Common sources of light such as the sun or a light bulb emit photons at random intervals, but as there are so many overall we see it as just a constant source.

Lasers provide a source of coherent light due to the way that they work. All the wavefront’s emitted from a laser line up with each other. We can use this source of coherent light to demonstrate interference from diffraction in by a single slit.

If the beam from a laser is shone through a fine slit, such as that between the edges of two razor blades, we can easily see how the waves are diffracted and produce interference. If the light from the slit is projected onto a paper screen we can observe and measure the patterns produced.

interference patternThis phenomenon is related to Huygen’s Principle. This says that every point on a wave front acts as a source of tiny wavelets that move forward with the same speed as the wave. The wave front at a later instant is the surface that is tangent to the wavelets.

Refraction and the Spectrum

refraction in a prismWhen light enters a denser medium is effectively slowed down. This is due to the light being repeatedly absorbed and re-emited by the atoms in the material. This slowing of the wavefront’s causes the beam to be bent at an angle dependent on the material and the wavelength (colour) of the light.

This image shows how white light is split into its component parts using a prism.

Electricity from Light

Homemade Solar Panels

This shows a simple demonstration of how a homemade solar panel can be used to show the photoelectric effect making electricity from light. Making a solar panel this way would be no where near good enough to generate useful free energy for powering a home, but it great for demonstrating scientific principles.

Solar PanelsOne sheet of copper is given a coating of cupric oxide as this semiconductor will convert sunlight into electricity. To do this a copper sheet is heated over a hob for around 30 minuets. When the sheet has turned black it is allowed to cool. As it cools down the black copper oxide will start to crack up and come off. this is because the materials underneath are contracting at a different rate. it is usually necessary to finish removing some of the black copper oxide by hand.

The remaining layer is covered with cupric oxide which is the important material for producing the photoelectric effect.

If the copper sheets are placed in a strong salt solution in the arrangement shown above, a small voltage will appear between the two sheets. The salt water is really just meant as an electrical conductor, but it also has the effect of making the device operate like a battery. this means it still generates small amounts of electricity even in the dark.

Electricity from Heat

Free Energy from the Environment

This is a simple setup that uses the thermoelectric / seebeck effect for converting heat directly into electricity with no moving parts. There are devices available called Peltier Heat Pumps which are used to keep electronic components cool.

Thermoelectric GeneratorThey are commonly used on processors as they can move heat away from a source under electrical power. When connected to a DC power supply a peltier element will heat up on one side whilst becoming cold on the opposite side. A large heatsink is necessary to dissipate the excess heat so that the other side can remain cold.

These peltier elements can also work in reverse. If it is heated on one side whilst being cooled on the other side a voltage will appear across the terminals. As long as there is a temperature difference between the two sides of the peltier device, then there will be a voltage between the electrical terminals.

Peltier heat pumps are not a very efficient method of generating electricity, but at least the supply of energy is free.

In a practical application a large heatsink could be buried in the ground to remove heat. If the peltier element is placed onto this is can be arranged to be heated on one side by the sun. A small black heatsink on the top of the peltier device could be used to collect heat from the sun that has been focused by a large mirror. Another method might be to use a larger heatsink and to place it inside a greenhouse. With this method it would be important to insulate between the hot and cold heatsinks so that the ground would not be heated directly.

Liquid Metal Experiments

Liquid Metal Experiments

Liquid Metal AlloyMost metals are a tough solid material at room temperature, but some metals can be liquids. The most obvious one is the element Mercury, which has a melting temperature of -38.83 °C. When certain metals are mixed together they can form what is known as an alloy. The atoms of the various metals will bond together to form the new metal which may have unique properties. Below you can learn how an alloy can be made at home which will melt in hot water. The alloys melting temperature is less than that of any of the original metals.

Using three common metals you can make a metal alloy which will melt in hot water. The metals are Bismuth, Lead, and Tin. Bismuth can be found in the form of ‘lead free’ fishing weights, and the other metals can be found together in the form of solder. Most solder is a mix of 60% Tin and 40% Lead, but for this experiment you will need the type that is 40% tin and 60% Lead.

A eutectic alloy is one where the ratio of the materials is made to give the lowest melting temperature possible. The eutectic alloy of Bismuth, Lead, and Tin would have the following ratios. 52.53% Bismuth, 32.55% Lead, and 14.92% Tin, by weight. The resulting alloy from this mixture can be expressed with the formula, Bi8Pb5Sn4. When mixed in the correct proportions this metal will melt at 95°C

Another liquid metal can be made that will melt at -20°C. This metal is made from gallium, indium, and tin.

As you can see from this image, This type of metal will easily stick to other materials. This is why mercury is still used in many devices.

Hydrogen Cannon

Hydrogen Cannon

Hydrogen Cannon DiagramThis experiment demonstrates the splitting of water into Hydrogen and Oxygen by electrolysis, and the re combining of these elements in an energetic reaction.

You can never recover the full energy from the Hydrogen fuel due to the lack of efficiency in the process used to make the hydrogen gas. During the electrolysis a current is flowing in the water to seperate the Hydrogen from the Oxygen, it is this current that produces wasted energy in the form of heat.

A plastic tube with one closed end has two electrodes inserted in the base so that they can be connected to wires on the outside. The electrodes should be made from carbon, but any conductor such as thick wire will do for this experiment. The space between the electrodes should be as small as possible but without them touching each other.

When the device is complete the tube should be filled with water until it just covers the electrodes. When the switch is pressed, the battery is connected to the electrodes and the flowing current begins to split the water into Hydrogen and Oxygen.

At some distance above the electrodes there are two more wires that are used for creating a spark to detonate the Hydrogen and Oxygen gas inside. The Piezo Sparker comes from a cheap lighter with click type ignition. When this is pressed it creates a high voltage that is used to create a spark. The two wires inside should be separated so that the spark will jump between them, and should be far enough from the water so that they don’t get drenched when the water is bubbling.

The projectile should fit snugly inside the end of the tube so that it doesn’t fall down to the water. It is important that this object is able to move freely enough to to leave the tube without a lot of resistance or else the whole thing could explode. The best type of projectile is a tube like the main one but slightly smaller so that it fits inside. If it is inserted so that the open end is down inside the larger tube the Hydrogen/Oxygen gas can build up behind it. As the tube is forced out when the gas is detonated it is forced to move in a straight line and can be more accurate than other shaped projectiles.

To fire the cannon the switch should be pressed for around 20 seconds depending on the electrodes and battery used. When enough gas has built up inside, the piezo sparker can be pressed detonating the H2 and O2 gas mixture. The gas expands rapidly forcing out the projectile and the product of the energetic reaction is just water again. The energy released in the explosion is almost the same as the energy supplied by the battery but it is released in a fraction of a second.