Check our facebook page for updates and special offers
A DIY Induction Heater
This great little project demonstrates the principles of high frequency magnetic induction. The circuit is very simple to build and only uses a few common components. With the induction coil shown here the circuit draws about 5A from a 15V supply when a screwdriver tip is heated. It takes approximately 30 second for the tip of the screwdriver to become red hot!
The control circuit uses a method known as ZVS (zero voltage switching) to activate the transistors which allows for an efficient transfer of power. In the circuit you see here, the transistors barely get warm due to the ZVS method. Another great thing about this device is that it is a self resonant system and will automatically run at the resonant frequency of the attached coil and capacitor.
How Does Induction Heating Work?
When a magnetic field changes near a metal or other conductive object, a flow of current (known as an eddy current) will be induced in the material and will generate heat. The heat generated is proportional to the current squared multiplied by the resistance of the material. The effects of induction are used in transformers for converting voltages in all sorts of appliances. Most transformers have a metallic core and will therefore have eddy currents induced into them when in use. Transformer designers use different techniques to prevent this as the heating is just wasted energy. In this project we will directly make use of this heating effect and try to maximise the heating effect produced by the eddy currents.
If we apply a continuously changing current to a coil of wire, we will have a continuously changing magnetic field within it. At higher frequencies the induction effect is quite strong and will tend to concentrate on the surface of the material being heated due to the skin effect. Typical induction heaters use frequencies from 10kHz to 1MHz.
The Circuit
The circuit used is a type of collector resonance Royer oscillator which has the advantages of simplicity and self resonant operation. A very similar circuit is used in common inverter circuits used for powering fluorescent lighting such as LCD backlights. They drive a center tapped transformer which steps up the voltage to around 800V for powering the lights. In this DIY induction heater circuit the transformer consists of the work coil and the object to be heated.
The main disadvantage of this circuit is that a center tapped coil is needed which can be a little more tricky to wind than a common solenoid. The center tapped coil is needed so that we can create an AC field from a single DC supply and just two N-type transistors. The center of the coil is connected to the positive supply and then each end of the coil is alternately connected to ground by the transistors so that the current will flow back and forth in both directions.
The amount of current drawn from the supply will vary with the temperature and size of the object being heated.
From this schematic of the induction heater you can see how simple it really is. Just a few basic components are all that is needed for creating a working induction heater device.
R1 and R2 are standard 240 ohm, 0.6W resistors. The value of these resistors will determine how quickly the MOSFETs can turn on, and should be a reasonably low value. They should not be too small though, as the resistor will be pulled to ground via the diode when the opposite transistor switches on.
The diodes D1 and D2 are used to discharge the MOSFET gates. They should be diodes with a low forward voltage drop so that the gate will be well discharged and the MOSFET fully off when the other is on. Schottky diodes such as the 1N5819 are recommended as they have low voltage drop and high speed. The voltage rating of the diodes must be sufficient to withstand the the voltage rise in the resonant circuit. In this project the voltage rose to as much as 70V.
The transistors T1 and T2 are 100V 35A MOSFETs (STP30NF10). They were mounted on heatsinks for this project, but they barely got warm when running at the power levels shown here. These MOSFETs were chosen due to having a low drain-sorce resistance and fast response times.
The inductor L2 is used as a choke for keeping the high frequency oscillations out of the power supply, and to limit current to acceptable levels. The circuit might work without it, but it is less efficient, and could lead to damage of the power supply or control circuit. The value of inductance should be quite large, but also must be made with thick enough wire for carrying all the supply current. If there is no choke used, or it has too little inductance, the circuit might fail to oscillate. The exact inductance value needed will vary with the PSU used and your coil setup. You may need to experiment before you get a good result. The one shown here was made by winding about 8 turns of 2mm thick magnet wire on a toroidal ferrite core. As an alternative you can simply wind wire onto a large bolt but you will need many more turns of wire to get the same inductance as from a toroidal ferrite core. You can see an example of this in the photo on the left. In the bottom left corner you can see a bolt wrapped with many turns of equipment wire. This setup on the breadboard was used at low power for testing. For more power it was necessary to use thicker wiring and to solder everything together.
As there were so few components involved, we soldered all the connections directly and did not use a PCB. This was also useful for making the connections for the high current parts as thick wire could be directly soldered to the transistor terminals. In hindsight it might have been better to connect the induction coil by screwing it directly to the heatsinks on the MOSFETs. This is because the metal body of the transistors is also the collector terminal, and the heatsinks could help keep the coil cooler.
The capacitor C1 and inductor L1 form the resonant tank circuit of the induction heater. These must be able to withstand large currents and temperatures. We used some 330nF polypropylene capacitors. More detail on these components is shown below.
The Induction Coil and Capacitor
The coil must be made of thick wire or pipe as there will be large currents flowing in it. Copper pipe works well as the high frequency currents will mostly flow on the outer parts anyway. You can also pump cold water through the pipe to keep it cool.
A capacitor must be connected parallel to the work coil to create a resonant tank circuit. The combination of inductance and capacitance will have a specific resonant frequency at which the control circuit will automatically operate. The coil-capacitor combination used here resonated at around 200kHz.
It is important to use good quality capacitors that can withstand large currents and the heat dissipated within them otherwise they would soon fail and destroy your drive circuit. They must also be placed reasonably close to the work coil and using thick wire or pipe. Most of the current will be flowing between the coil and capacitor so this wire must be thickest. The wires linking to the circuit and power supply can be slightly thinner if desired.
This coil here was made from 2mm diameter brass pipe. It was simple to wind and easy to solder to, but it would soon start to deform due to excess heating. The turns would then touch, shorting out and making it less effective. Since the control circuit stayed relatively cool during use, it seemed that this could be made to work at higher power levels but it would be necessary to use thicker pipe or to water cool it. Next the setup was improved to tolerate a higher power level...
Pushing it Further
The main limitation of the setup above was that the work coil would get very hot after a short time due to the large currents. In order to have larger currents for a longer time, we made another coil using thicker brass tubing so that water could be pumped through when it was running. The thicker pipe was harder to bend, especially at the center tapping point. It was necessary to fill the pipe with fine sand before bending it as this prevents it from pinching at the sharp bends. It was then cleared out using compressed air.
The induction coil was made in two halves as shown here. They were then soldered together and a small piece of pvc pipe was used to connect the central pipes so that water could flow through the whole coil.
Less turns were used in this coil so that it would have a lower impedance and therefore sustain higher currents. The capacitance was also increased so that the resonant frequency would be lower. A total of six 330nF capacitors were used to give a total capacitance of 1.98uF.
The cables connecting to the coil were just soldered onto the pipe near the ends, just leaving room for fitting some PVC pipe.
It is possible to cool this coil simply by feeding water through directly from the tap but it is better to use a pump and radiator to remove the heat. For this, an old fish tank pump was placed in a box of water and a pipe fitted the outlet nozzle. This pipe fed to a modified computer CPU cooler which used three heat-pipes to move the heat.
The cooler was converted into a radiator by cutting the ends off the heat pipes and then linking them with PCV pipes to the the water would flow through all 3 heatpipes before exiting and going back to the pump.
If you do cut some heatpipes yourself, make sure to do it in a well ventilated area, and not indoors as they contain volatile solvents that can be toxic to breathe. You should also wear protective gloves to prevent skin contact.
This modified CPU cooler was very effective as a radiator and allowed the water to remain quite cool.
Other modifications needed were to replace the the diodes D1 and D2 with ones rated for higher voltages. We used the common 1N4007 diodes. This was because with the increased current there was a larger voltage rise in the resonant circuit. You can see in the image here that the peak voltage was 90V (yellow scope trace) which is also very close to the 100V rating of the transistors.
The PSU used was set to 30V so it was also neccesary to feed the voltage to the transistor gates via a 12V voltage regulator. When no metal was inside the work coil, it would draw about 7A from the supply. When the bolt in the photo was added, this went up to 10A and then gradually dropped again as it heated up beyond curie temperature. It would certainly go over 10A with larger objects, but the PSU used has a 10A limit.
The bolt you can see glowing red hot in the photo took about 30 seconds to reach maximum temperature. The screwdriver in the first image could now be heated red hot in about 5 seconds.
In order to go to higher power than this, it would be necessary to use different capacitors or a larger array of them so that the current was more distributed between them. This is because the large currents flowing and high frequencies used would heat the capacitors significantly. After about 5 minutes of use at this power level the DIY induction heater needed to be switched off so that they could cool down. It would also be necessary to use a different pair of transistors so that they could withstand the larger voltage rises.
In all this project was quite satisfying as it produced a good result from just a simple and inexpensive circuit. As it is, it could be useful for hardening steel, or for soldering small parts. If you decide to make your own induction heater project, please post your photos below. Please read through the other comments before making your own as it could save you time later on.
If you wish to simulate this project for testing different inductance values or transistor choices, please download LTSpice and run this DIY Induction Heater Simulation (Right click, Save as)
Troubleshooting
If you have trouble getting this working, here are a few tips to help troubleshoot your home made induction heater project....
PSU (Power Supply)
If your PSU is unable to deliver a large surge of current when the induction heater is powered on, then it will fail to oscillate. The voltage from the supply will drop during that moment (although the PSU may not display this) and this will prevent the transistors from switching correctly. To help with this problem, you can place several large electrolytic capacitors in parallel with the supply. When charged they will be able to deliver a large surge current to your circuit.
Choke (inductor L2)
This limits the power to your induction heater. If yours is not oscillating, then you may need more inductance to prevent voltage drop in your PSU. You will need to experiment with how much inductance you need. Better to have too much, than too little as this will only limit the power of the heater. Too little may mean it wont work at all.
Wiring
Keep the connecting wires short to reduce stray inductance and interference. Long wires add unwanted resistance and inductance to the circuit and can result in unwanted oscillations or poor performance.
Components
The transistors chosen must have a low voltage drop otherwise they will overheat, or even prevent the system from oscillating. The capacitors must have a low ESR (resistance) and ESL (inductance) so they can tolerate the high current and temperatures. The diodes should also have a low forward voltage drop so that the transistors switch off correctly. They should also be fast enough to work at the resonant frequency of your induction heater.
Powering it up
When switching it on, do not have metal within the heating coil. This can lead to larger current surges which could prevent the oscillation from starting as mentioned above. Also do not try to heat large amounts of metal. This project is only suitable for small induction heaters.
Brain
You will need a brain that functions reasonably well to make this project safely. If you are one of those people who is known by your friends as "a bit thick", then congratulations on being able to use a computer and navigate to this page, but unfortunately this project is not for you. It can be very dangerous to build an induction heater, so if you are new to electronics, you should get someone to help you make it. Approach things logically; If it is not working, check the components used are not faulty, check connections are correct, read this whole article and all the comments, search Google if you do not understand any of the terms, or read through our Learn Electronics section. Remember: Hot things will burn you and can set things on fire; Electricity can electrocute you and also cause fire. Put safety first.
The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.
What is the red waveform on the scope?
The red waveform is the gate voltage of the other transistor.
Yes you can.
Rusdi,
There is also the temperature hazard, and then potentially chemical hazards if components get burned. The scope is not needed, but was useful for seing the waveforms and frequency. The scope ground should be the same ground as your PSU. you can then measure at the MOSFET gate, or collector terminals. If you measure at the collector, remember that the voltage could be much higher than the supply voltage so set the scope accordingly.
Surastyo.
I can't seem to find the datasheet for that part number. What are its ratings? They are typically set as GDS, but you need to check the manufacturers datasheet. I also do not see any large inductor (L2) in your picture. I've attached a diagram showing the 7812 voltage regulator being used.
I think 60V is much too low of a voltage rating for the MOSFETs. THey are probably being destroyed by over voltage.
To get hotter temperatures, you need to use more powerful transistors and capacitors, and then use a higher supply voltage.
We don't have anything else available at the moment. You would just have to look for components with larger voltage and current ratings.
Martin, If you are not getting nice sinusoidal oscillations, this could be due to having too little, or even too much inductance in your choke (L2). You may need to experiment with different choke designs to find something that works well with your other parts. Your work coil should ideally be only a little larger than the object to be heated as this will maximise the concentration of magnetic flux. If that does not help, add a photo of your scope showing the gate voltage, and drain voltage waveforms.
Joco, I can't find that part number. Did you make a typo?
Tohooloo, C1 can be as large as you like. The combination of capacitance of C1 and the inductance of L1 form a resonant circuit. A larger capacitance or inductance will result in a lower frequency.
Joco, That MOSFET seems ok. Try using a larger choke (L2).
Neither. You need higher power.
Deyan,
It sounds like your capacitors have too much internal resistance (ESR). You need something that is better for high power, they are typically much larger in size for the same capacitance value. There are many types of transistors that may work, but it is up to you to test if the ones you have are ok. I suspect that a high voltage IGBT will have too large of a voltage drop between collector and emmiter which would mean that the opposite transistor would not switch off properly. I used these 100V, 35A MOSFETs which worked well.
Stephen,
I used these 1000V, 330nF capacitors.
I can only suggest you follow the instructions given. If you use other components, they may or may not work. That is up to you to work out.
1. All those factors will vary the performance. The number of turns will determine the impedance of the coil and therefore how much current will flow for a given frequency. Less turns will allow for higher peak current, but too few and the transistors will blow.
The coil diameter should ideally be just slightly larger than the workpiece that is to be heated. This maximises the field coupling and is more efficient.
The capacitor size will also determine peak current. larger is better, but not too large or the resonant frequency will become too low. Physically larger capacitors will have low internal resistance too so they will perform much better. The bank of caps in your picture look way to small for the amount of metal you are trying to heat.
2. You should get a nice half sine waveform. You need to experiment witht the inductor (L2). Try different numbers of turns until you see some improvement. You could also add 15V Zener diodes between the gate and source pins of each transistor to help protect them from voltage spikes.
3. V+ can be as high as you like, just make sure your components are sufficioent to handle the voltage rise in the coil. You will also need to supply the gates from a stable 12V source.
4,5,6. See other answers.
You can use a single power supply, or seperate ones. If using a single supply it should be at most 15V, or 30V if you use the regulator as shown in another post.
Your power supply is not able to deliver enough current. You need a bigger supply, or many more turns on the work coil or choke.
Yes
The current will depend on the voltage you apply, and the load impedance. More turns on your work coil, smaller capacitors, and larger choke inductance will reduce current.
Nice job. Thanks for sharing Rob.
James,
If you Google the part numbers you will find the manufacturer pdf datasheets. These will tell you which pins provide a particular function. I think it is best you try working this out yourself as you will gain a better knowledge and understanding. You can also check out the section on the site for helping to learn electronics as it will explain a lot about the components and the physics of the electronics involved.
Chanil,
Yes, if you want to limit the current to 1A, then you must increase the impedance of the circuit. Using many more turns in your work coil and the choke will limit the current.
Chanil's video...
ad,
You can reduce C, but you will need t make sure that the remaining capacitors you have are able to take all the current. The advantage of using lots of capacitors is that the current is shared between them.
Eric,
What you describes just sounds like it is due to the limitations of your PSU. Remember that voltage and current are directly related and will be affected by the impedance of your load. If your PSU shows low volts, and high amps, this indicates that the impedance of your circuit is low and your PSU is dropping the volts to keep the current within its ratings.
Yes, it would seem that you just have DC flowing at low voltages
Your MOSFET needs to be able to withtsand the peak current. Measure the DC current your coil draws from your supply whehn you apply 120V. I suspect you need more turns on your work coil and choke.
David, yes.
Hampus, Both. The first version uses the 40V ones, later when more power is used, the 1000V ones are used.
Benjamin,
Maybe it is the 19V supply. Make sure you use a regulator for the gates as shown in a previous post.
Chris,
Yes the choke will limit the current, but only as long as it is oscillating. You should work based on the impedance of half the work coil.
It might be possible to parallel some MOSFETs, but you would need to make short neat connections otherwise they may suffer from interference problems.
The STP30NF10 is used in both versions. We used 4mm brass tube, with a coil radius of 25mm.
You would need some type of interrupter circuit and then vary the pulse width of the interrupter. For example; You could use one of our Power Pulse Modulators set to a low frequency to supply the power to the circuit. Adjusting the pulse width setting would proportionally adjust the power in the heater.
Hans,
You would also need a very large smoothing capacitor, but it could work.
whisk,
If your solder is melting so quickly it is probably because your wire is too thin. You need to make the coil from very thick wire or copper pipe.
It looks OK. Is there any reason the tips cant be closer together, or even placed end to end? Separating the two halves of the coil means that the field in each coil will oscillating in strength, rather than alternating polarity as you would have when the coils are together. You would really be better off having two separate circuits and coils as it would be most effective.
Hans, Most losses will come from resistance in the components. Mostly in the coil in this case, but losses in the capacitor are not insignificant. It is important to use capacitors with a low ESR. You have things a little mixed regards to altering frequency. Increasing either inductance or capacitance will lower the frequency. At higher frequency there will be more losses in the capacitor dielectric, and also in the coil due to the skin effect. The skin effect would also mean that at high frequencies the heating would be concentrated in thinner layers on the surface of material sample.
Justin, Yes, the voltage rises as described in the article would mean that exposed terminals or the coil could have high voltages present. You should avoid letting the heated object touch the coil as it could short circuit and damage your transistors.
wellington, I have no idea what you are talking about. Nicollas, I do not really understand all you wrote either, but it sounds like your circuit is not oscilating. If you are also using different diodes, it could be because they have too much voltage drop which prevents the transistors from being switched.
No. The resistance of the coil would be too high. The losses in the coil would cause it to get very hot and waste a lot of power. Copper is the best material to use. Brass was only used here because we had the pipe in our workshop and it was small enough for making this simple demonstration.
Nicollas, Mike; Use the diagram in post 4649 that includes a voltage regulator. Use a bigger choke, and place a large capacitor parallel to the PSU to help it cope with current surges.
Mike, Andreas, The inductor L2 serves as a choke to prevent high frequencies reaching your power supply, and also as a ballast to limit current. The calulations will depend on your operation frequency and desired current. 22V is fine, but you will need to feed the gates via a regulator as shown in a previous post. You should probably use more than four capacitors.
Andreas, 6 or 8 will work OK. Using 8 may share the current a little more and therefore not heat up so much. Reg, the temperature of the MOSFETs will depend on the current flowing and the frequency. If the frequency and current is quite high, it is normal for them to heat up. Try using a larger heatsink, or MOSFETs with a lower drain-source resistance.
See the calculations posted by kevin in post 4817. With a 36V input and IRF540 transistor you are likely to blow the transistors. As shown in the article our 30V input was causing it to push close to the limits of the transistors used.
reg, if the gates are not switched on with a high enough voltage, the transistors will heat up significantly. Waheed, adding a large object in the coil will increase current demand a lot. if you want to limit the current, use a bigger choke (L2).
A straight bar is ok, but will need more turns compared to a toroid. Those caps should be ok as long as they are capable of withstanding large currents and high temperatures. You can just link the ends using some PVC pipe as long as the copper is connected together too.
Try using a much much bigger choke, and regulating the voltage used to feed the gates. Make sure the supply to the gates is well regulated and filtered.
Grant, The radiator is a modified CPU cooler from a computer. I think this one came from an old DELL PC.
Steve, The voltage rise in the circuit will be about 3.14 times your input voltage. But your capacitors voltage rating should be significantly larger so that they are not being pushed to their limits. I would suggest using one rated for at least 6 times your input voltage.
Are brake lines stainless steel? That has a high resistance, as do thin wires. You need to use thick cable or pipe that is highly conductive.
Looks ok. You can try the caps you have but they may overheat quite easily.
Looks ok, but dont let your heatsinks touch together or you will just be causing a short circuit. Fit a capacitor to the output of your regulator too, that will help smooth out any noisy power line. Something like 330uF or more.
Daniel, Andreas,
Make sure the supply to the resistors is regulated and smoothed with a capacitor.
Check that your supply is capable of providing the peak current demanded by your coil.
Decouple the supply to the gates by placing a capacitor from 12V to GND while keeping the connections as short as possible.
Place a 12 to 15V zener diode between the gate and source of each MOSFET (cathode to the gate). This can help reduce noise and protects the transistors.
Try replacing your choke with something with huge inductance so that power is limited significantly. You can use an ordinary mains transformer for this. Just use an output winding as the choke. If it still wont oscillate, make sure you don't have a dud transistor or diode somewhere.
You should just replace both MOSFETs in your induction heater to be sure. Yes, pretty much any low power transformer will have enough inductance to limit the current to a couple of amps or less. It will be useless for significant heating, but allows you to test if it is oscilating without blowing components. You may also want to add zener protection to the transistor gates.
See post #4649 for a diagram including a regulator. Yes, the capacitors in your induction heater must be low ESR otherwise resistance losses will soon heat them to destruction. Yes, copper is better due to lower resistance. Brass was used simply becasue we had some available at the time. I've since built one with copper which I will post later, but I did not see any noticable performance difference and the heater coil still needed to be water cooled.
Iron based metals heat well because of hysteresis losses and conduction losses. Metals like copper and aluminium can be more difficult to heat partly due to higher conductivity.
The magnetic field is strongest at the inside edge of the coil. The skin effect also forces heating to concentrate on the surface of a material.
Place something metal in the coil and see if it gets any warmer.
Frank, The diagram is ok. You should only use one regulator. The way the connections switch on and off the gates is described in the article.
Aamer, Show us your work coil and iron rod.
I still think you need a bigger choke. The huge inductance of the transformer winding is allowing it to oscillate, so you just need to find the right iinductance value for your setup. When powering up the induction heater, I would suggest that you do so without any metal within the coil, then add the metal after.
Yes, I think you will need to experiment with what works best with your specific PSU and heating coil. You could also try using a Power Pulse Modulator between your PSU and the induction heater circuit. This would allow you to vary the power to the heater. You woild set the frequency settng to a low value like 20 Hz, then you can adjust the duty setting from 0 to 100% to give you a 0 to 100% adjustment in heating power.
Your PSU is not able to meet the peak current demaned by your setup. When you first connect power, there will be a surge of current which is mostly limited by your choke (L2). Use a bigger choke, and add some large capacitors to your PSU.
See the troubleshooting section I've added to the end of the article. You don't tune your induction heater. It automatically works at the resonant frequency. The link I gave you is to a product which will allow you to limit and control the input power so that you do not blow your transistors while testing it. I don't think adding another DIY circuit is going to help you, as it just increases complexity. Adding 1 turn to your choke is going to make little difference. Add something like 20 turns. I really do not think there is anything else left to suggest to you. If you are following the article and all the advice, but it is still not working, then you must have faulty parts, wrong connections, or a PSU that is not up to the job.
While I can't comment on every individual transistor model anyone might use, I can suggest that if you use one with longer rise/fall times, you could compensate by using a larger capacitance to lower the resonant frequency of the system.
It only becomes an issue if the rise/fall times are a significant value compared to the period of the operating frequency of the circuit. The transistors are switching when the voltage (between source and drain) is almost zero. Just work out what the switching time is as a percentage of the period. By minimising this value, the switching losses are reduced. In this circuit you would probably be more concened with conduction losses due to high currents unless you need it to operate at some very high frequency for some reason.
No they wont. That looks like a polystyrene capacitor and judging by the thickness of the wires, it is not meant for high currents. You need to use polypropylene capacitors or an equivalent that is specifically made for high currents. For larger objects you need more power.
This link should answer that for you.
You should allow more time for your load to heat up. I've added a spice simulation to the article just above the troubleshooting section. The STP40NF10 was not in the library so I just chose something else in the library. Run the simulation then check out the collector waveforms and inductor current. The simulation does not include any load, but you can add this if you wish. I'm not here to answer questions on how to use LTSpice though.
You are using different components and some kind of DIY power supply. You will of course not get the same results.
Lol, the spice file is fine, I really don't know what you must be doing. You will need a higher input voltage than 12V to get heating like shown in the video (I used 30V). Have you also considered that your capacitors may be damaged, or just not up to the job?
This is the result obtained by me. was very good and oscillates at frequency of 75kHz. Thanks for the help RMcybernetics and friends.
Aamer, It is already an asc file. I don't know why you renamed it. Yes 12V will work but of course less powerful than 30V. As mentioned multiple times, the capacitors need to be quality polypropylene or equivalent. It may oscillate when using other caps, but the performance will be poor. If they are damaged by voltage spikes, that will also prevent proper operation.
Nicollas, Thanks for sharing. Nice build quality.
Charles, please read through the other comments. As mentioned already, brass was only used because it was available at the time. Copper pipe would be better. Yes you can use whatever coil shape you like. However the heating effect may not exactly match the shape as the magnetic interactions and shape of the object will dominate the effect.
Hello i build you heater, and it works ok....Now i want more power....but i hav one question... If i use bigger FET's / IGBT,up to 600v and 150A (MG150Q2YS40).. Can is use the same diodes to the gate, i think the power over the gates will be more than 20 volts....
You can not just replace the transistors with power IGBTs. The saturation voltage of the transistors would be too high, preventing proper switching as explained in the article. A different and more complex circuit would be needed.
The link is directly to an asc file. You can click to view it, or right click and save it to your computer.
The simulation does not include any load and is not accounting for the losses in the system which is why it only draws a low current. You should observe the voltage on the 30V supply. During the first moments it will drop very low which could prevent oscilation in a single supply system if not accounted for. You should also consider the initial voltage spike as this could blow any of your components. Try this simulation. It will not oscilate becasue the PSU has too much internal resistance. Run it, you will only see DC, then alter the resistance to something lower and you will see it begins to oscilate.
Yes, add the regulator and zeners as suggested.
Yes, use a single 24V supply and regulator for the gates. When using two supplies, did you create a common ground? You could change the MOSFETs if you like, just choose good ones with low resistance and high speed.
Well the STP30NF10 used here does fine even with 30V input if you have a regulator and zener protection on the gates, but you can try other transistors if you want.
There's nothing else I can suggest.
Looks nice. DId you etch your own PCB? You may want to reinforce the PCB traces from the caps though as they will be carrying a lot of current. You can see the regulator diagram in post 4649. The zeners would just go between the gate and source with the cathode to the gate
It would heat it, but I would not call it a furnace. You may even struggle to get it red hot. Once such a large load is placed in the coil, the current draw will rise significantly, and quite probably need more than 5.5A. We will however post a new project in future which allows for higher power levels.
You can't use this circuit at those voltages. You would need a different, more complex setup which is beyond the scope of this article.
Links to all the available parts are in the article. If you add them to your basket, you can get a shipping price calculated automatically.
As long as the water is not contaminated with significant amounts of electrolyte (like in salt water), then the length of tubing should make the total resistance so high that any current flowing in the water would be neglegable.
2n3055 is not suitable. Use the MOSFETs mentioned in the article.
Vgs does not determine Vds when the gate is saturated (such as above 10V). The voltage applied to the gate here is 12V, but the voltage from the supply for the rest of the circuit is 30V. When a 'Tank Circuit' (inductor and capacitor in parallel) is pulsed, it will resonate at its fundamental frequency. If the Q factor of the circuit is good enough (there are not significant losses through resistance etc), then there will be a resonant voltage rise in the circuit. The peak voltage here will be about pi x input voltage which is why we get about 90V from 30V input.
The power actually builds up in the LC tank circuit. Once running, the current drawn from the supply will be less than what is actually flowing in the induction heater circuit. Try the simulation in the article to see this.
Farhad, The choke in the induction heater is to separate the high frequency oscillations from the PSU, and to limit the current flow. This also helps ensure you get a good sine wave output. When oscillating well, the frequency should be pretty close to 1/2pi*sqrt(LC) where L is the combined inductance of the two halves of the coil. Adding a load will also alter this. The simulation does not take in to account many factors such as the specifics of your PSU, or parasitic components.
Joseph, Yes 12V will limit the power. You may not need the additional regulator, but I would recommend it as it helps protect your transistor gates and ensure smooth operation.
Joseph, If it has +12V and -12V then just use the -12V as your GND connection. This gives you a 24V supply.
Trevorb, Bigger choke.
I've used 500uH in the simulation. 2.8uH is way too small. Please read through the other comments and troubleshooting section carefully. I have mentioned this multiple times.
Just use the -12V in the same way as GND is used in the diagrams. It will work just fine. You don't need to treat it any differently than an ordinary 24V supply. You can find torroidal cores inside old amplifiers or computer power supplys.
Frank, Cons are limited power and needing a center tapped coil. You would need capacitors that are specifically designed for very high current, high frequency use.
Dimitris, You can add parallel MOSFETs if you need more current handling.
Rajesh, No, it must be the coil.
You can use pulse width modulation to control the power. I found that our PWM-OCm works very well. To use it, I connected a diode between the gate terminal of each MOSFET, and the L- connector on the Power Pulse Modulator. The cathode side of the diodes connects to L-.
You also need to power the OCm from the same power source, or create a common ground if using a seperate one. When the OCm switches on, it pulls the MOSFETs low, thus disabling the induction heater circuit.
You can now adjust the modulation frequency and duty very easily. Note that the duty control is inverted when doing this.. i.e. turning up the OCm to 100% will set your induction heater to 0%.
Frank, there is allready a gate resistor. Increasing this will slow down the switching and increase losses. To protect the gate, use a zener diode between gate and source.
Rajesh, No, just do as described.
Sachin, It could work in theory, but that is not a practical circuit. I can only offer support for the circuit in this article.
This is not the place for getting support for your cooker. Contact the manufacturer. This is only for information and support for the DIY Induction Heater project above.
A car battery has a huge current capacity. The problem with this is that the sudden rush of current when connecting the circuit could blow the transistors before the oscilation even gets started.
I would suggest using a PWM so that you can slowly turn up the power. See post #5013
The inductors are described in the article and comments. Nothing needs to change for a wider coil, but you may find that it will not heat large items so well.
Robert, The specifics of the choke and work coil do not need to be exact. We soldered the wire directly to the side of the pipes, but leaving enough space from the end so that water cooling pipe can pe pushed over.
Sam, You will need to use a PWM as suggested in post #5013. If you set the pulse frequeny to something much lower (50Hz is fine) than the resonant frequency, then it will not cause any oscilation problems. Your arduino can be programmed to disable the PWM when it detects the temperature i s too high, then re set it agoun when it has cooled a little.
Sara, a full bridge would be a different system altogether. I can not offer any help for that as it too far outside the scope of the article.
We do not currently sell an assembled unit. We will have some new products available soon for making induction heaters. Check our Facebook page or newsletter for updates.
1) Because the current is delivered to the center of the coil, then each transistor switches alternately so that current flows in both directions.
2) Probably, but it will not be simple. The material, size, shape, and position in the coil will all effect the heating. There is also the frequency, current, and coil dimentions to consider.
Yes you can, allthough you may find the solder melts if not kept cool. More capacitors is better as it helps share the current and reduce frequency.
I am not sure there is anything else to suggest. There are a lot of tips in the article and comments. You will have to work through those :)
The center tap does not need extra cooling. The large currents circulate between the coil and capacitors. For extended high power use, you might need to cool the capacitors too. The PWM will not heat up as it is only controling the transistors and not switching any significant power directly.
Facepalm! Please read and follow the troubleshooting tips and the other suggestions throughout the comments.
A 9V (PP3) battery does not have enough power to heat a cup significantly. There is no point using induction heating for this anyway. Just a standard resistance heating element would be best.
I have an old yaskawa V1000 drive for induction and pm motors would i be able to use this as an induction heater or salvage parts from it
No, it may contain some useful transistors, but you would be better off just buying the few parts that this project requires.
Hi, I've been trying to find an affordable 0.1uf capacitor to use in a chain of 40, for a total capacitance of 4uf. I found two such models: The first is significantly cheaper, but it is described as "General Purpose" vs the more expensive "AC Pulse, Suppression" model. Also, the second model is "Double Metallized". Are these features necessary for a ~600W heater, or can I go with the cheaper model? Thanks!
bob, Neither will be suitable. You can not cheap out on parts if you want to make it work at 600W.
Michael, No. The arc welder output is very low voltage. You can not just replace the MOSFETs with IGBTs. As mentioned in the article, the voltage drop would be too large and would not allow the opposite transistor to switch off
This circuit is just a simple DIY induction heater project. It would require something more complex and using more expensive parts to work at significantly higher power levels.
Christopher, Absolutely the PSU is not good enough. This is the number one point in the troubleshooting section. Please read the whole article and comments. The answers are there.
bob800, they basically wont have enough metal inside them or at the connections to support large flows of current. The ones used in this project are only able to withstand short runs at 300W. The 1000V rating is not going to help since in this project the voltage only increased to around 100V.
Ian, Too big is OK, too small could just mean not enough inductance. The one used here is 550mm od and 18mm thick. I spread the turns but it wont make a significant amount of difference.
The solid wire might be easier for forming a coil, but apart from that, either will be OK. This diagram shows the addition of 2 diodes to the circuit so that it can be linked to one of our PWM Control circuits for adjusting the power of the induction heater.
The duty control of the pwm circuit is inverted compared to the output power of the heater. which means setting the duty to 100% will turn off the heating. So before turning on the power, set the duty control to 100%. You can then gradually adjust it so that the heating and flow of current is at the level you want. Any of our PWM circuits will work for this as connecting this way does not pass the main power flow through the PWM. You should also set to quite a low frequency such as 50Hz as this seems to allow the induction heater to resonate properly between pulses.