Induction heaters are used to heat conductive materials in a non-contact process. Commercially, they are used for heat treating, brazing, soldering, etc., as well as to melt and forge iron, steel, and aluminum.
This Instructable will walk you through the construction of a high-power (30kVA) heater, suitable for melting aluminum and steel. Note that to take full advantage of this design, you will need a 220V outlet, at least a 50A single-phase one and preferably a 50A or 60A 3-phase outlet.

About the author:

Bayley Wang (me) is a EE student at MIT. I'm responsible for a variety of nefarious power electronics projects which you can find on my blog; perhaps most interestingly is oneTesla, which has since gained a life of its own as a startup creating DRSSTC kits.


  • This project uses mains voltage. While well-behaved, 110/220 mains can seriously injure, maim, and/or kill you if used improperly.
  • The voltage across the tank capacitor can potentially ring up to hundreds of volts. Don't let the 20:1 step-down ratio fool you!
  • When scoping the circuit, beware of ground loops.
  • The work piece, naturally, can get very hot. DO NOT TOUCH! Less obviously, do not rapidly quench the work piece with water, as this can lead to dangerous sputtering.
  • This project uses power electronics. Under fault conditions, semiconductor devices used in this project may rapidly heat, vent, and/or release rapidly moving shrapnel. Shield appropriately.

WIth that said and done, let us move on.

Step 1: Bill of Materials

For this build, you will need:
  • 2 IGBT half-bridge modules. I used Powerex CM400DU-12F 400A 600V Dual IGBTs; anything of similar power handling and switching speed should work. These can be purchased as cheap surplus from Ebay.
  • 4 MOSFETs or IGBTs for the gate drive. I used HGTG30N60B3D's, which are way overkill for the application. They need to be able to dissipate about 30W without burning up.
  • 2 gate drive IC's, of at least 9A peak current capability. I use the UCC37322 from TI.
  • 2 ferrite toroids. These are your gate drive transformers, and should be able to pass a reasonably clean square wave at 50 kHz. Magnetics, Inc. and TSC Ferrite International are good manufacturers, or you can salvage them from old CRTs or switching power supplies. The powered iron cores from ATX supplies rarely work.
  • Large ferrite toroids for the toroidial coupling transfromer.
  • 1 TL494 PWM IC.
  • 1 at least 20 uF, at least 20V film or ceramic capacitor.
  • Assorted resistors, capacitors, and potentiometers for the driver.
  • 10' of 1/4" soft copper refrigeration tubing.
  • A water block capable of accommodating the two IGBTs. A large heatsink may also work, but I haven't tried.
  • 2 aluminum or copper bars, ~3/4"x8"
  • 2 1/4" compression unions
  • A 4-position rotary contactor, good for several tens of amps.
  • A screw-terminal electrolytic capacitor of reasonable quality. I recommend at least a few hundred uF for 3-phase operation.
  • A high-quality, low inductance snubber capacitor for the bridge. Ebay has cute brick-mount 20 uF blocks for $5.
  • One or more high-quality polypropylene capacitors for the tank capacitor. More on this part later.
  • An analog current meter good for several tens of amps.
  • A 3-phase bridge rectifier (or single-phase if you are willing to settle for single-phase operation only).
  • A suitable project case and associated hardware (3-phase breaker, cord, plug, etc).
  • A water pump capable of a couple GPM
  • Tubing appropriate for hooking up the water-cooling.
  • A Variac for testing.

Step 2: Words of Wisdom

The IGBTs: or "bricks", as we like to call them. They should be good for 600V (not a concern, I've never seen a brick rated under that before), at least 200A (I use 400A modules to be, safe), and more importantly, need to be fast. This is where you need to check the datasheet - IGBTs have an inherently long turn-off delay. For 65 kHz operation, rise time + turn-on delay + turn-off delay + fall time should be under 2 uS.
Bricks come in several types: single-transistor, dual transistor, 6-pack, and some rarer types such as chopper modules. Single-transistor modules are prevalent for 1200V and larger IGBTs, and have the highest thermal ratings and are the most difficult to mount. Duals (half-bridge modules) are the much easier to mount and can dissipate less. They are most common for 600V modules. 6-packs are used for 3-phase inverters, require no external power connections, and have the lowest thermal ratings.
Use what you see fit; this tutorial uses half-bridge modules.

The tank capacitor: is very very important. It handles tremendous amounts of reactive power at very high frequencies. It is absolutely essential that this part be selected appropriately. It must be a high-quality polypropylene or mica capacitor. I use giant snubber capacitors made by Eurofarad; alternatively, a series/parallel array of smaller capacitors (such as the Tesla coiler's beloved CDE942 series) should work. The ultimate capacitor, of course, is a water or conduction-cooled unit made by Celem, but such caps will run you about $150 for a 2 uF unit. You want enough capacitance to resonate with your work coil at no more than 70 kHz.

Step 3: Principle of Operation

Induction heaters function by surrounding the work piece with a coil carrying a high-frequency (kHz to low MHz) alternating current. This induces eddy currents in the work piece, which acts as a shorted 1-turn transformer secondary. The currents can be tremendous, on the order of several thousands of amps. This causes high I^2R losses in the work piece, heating it.

Schematic Description
Ignore the transistor model numbers; I just used what Eagle had built in.

IC1 is a TL494 acting as an oscillator with adjustable dead time and frequency. The output is fed into the input of two UCC37322 9A gate drive ICs, which "beef up" the signal into something capable of driving high-capacitance transistor gates. The output signal is passed through C5 to insure only the AC component reaches GDT1, a gate drive transformer. This transformer provides the electrical isolation necessary to drive Q1 through Q4, which form a full-bridge. This intermediate bridge is necessary to provide the high average power necessary to drive Q5 through Q8, a full-bridge of large IGBT modules.
This bridge forms the main inverter. The output of this inverter is stepped down through a 20:1 torodial transformer TR_MATCH, which provides impedance matching as well as isolation for L_WORK, the work coil inductor. The capacitor C_TANK forms a resonant LC circuit with L_WORK; when driven at resonance, this circuit displays zero reactive impedance to the inverter, allowing for higher powers and minimizing switching losses in the inverter.

Step 4: Construction: Controller

Construct the logic circuit as you wish, either by using the attached images to make boards or using perfboard or a breadboard.
The gate drive transformers must be able to pass a high-quality square wave at your operating frequency. To check this, wind 10+10 turns on the toroid, connect one set of windings to a signal generator, and scope across the other. The output should look like a reasonable square wave.
The GDT should be wound with 5 twisted wires to minimize leakage inductance. Many people have had luck with using CAT5 cable, which comes pre-twisted.

Step 5: The Inverter

The inverter should be very well-cooled, either with a large heatsink or a waterblock. I used a waterblock for compactness and robustness; but a big (think 12"x12"x3" with several hundred CFM of forced-air cooling) should work too. The pump should be relatively large to handle the pressure drop through the work coil (mine was rated for 2GPM).
The main filtering capacitors should be placed close to the bridge itself, preferably bolted across the busbars. You should also use a snubber capacitor (the black box in the picture) placed directly across the transistors to reduce voltage spikes caused by excitation of the parasitic inductances in the inverter layout.
Using half-bridge or six-pack modules is the easiest way to buld the inverter; a bridge of single transistors will require access to a machine shop to do right.

Step 6: Work Coil/Tank Circuit

The coupling transformer should be toroidal. Wind ~20t around some large ferrite cores (I was using a stack of 4 ~4"x1" cores).
The tank capacitor will get warm. It should have significant terminal area to conduct both heat and thousands of amps. If you are using a MMC of small capacitors, solder them individually to large copper plates. If you are using a Celem or a giant snubber, bolt large copper plates to the terminals. Then in either case, solder the terminals to the copper tubing that forms the rest of the tank circuit.
Attach the work coil to the tank circuit using compression fittings; this allows you to change work coils to accommodate different loads.
Make the work coil out of at least 1/4" copper tubing. Thicker tubing is less lossy, but harder to handle; trade-off between the two as you see fit. When winding the work coil, it helps to fill it with sand to prevent the tubing from collapsing. As a rule of thumb, the resistance of 1' diameter copper tubing at 65 KHz is 0.8 mΩ/m; that is, to compute the resistance of your secondary, multiply 0.8 mΩ by its length and divide by its diameter in inches.

Step 7: Testing and Usage

Assemble everything according to the schematic. Use a current transformer on the primary side (100t burdened with a couple ohms around a ferrite toroid will do) to monitor the waveforms.
Using a current-limited bench supply (preferably 30V, 10A), slowly ramp up the voltage until enough current is drawn to give a clear reading on the 'scope. Adjust the frequency pot until the waveform is a clean sinewave, and current draw is maximized (you may have to search a little to avoid harmonics). If you don't have a scope, just tune until current is maximized (mine drew something like 40A at 200VDC on the bus, unloaded).
With ~30V on the bus, load the work coil with a bolt. At a few hundred watts in, it should get hot within a couple minutes. If it draws power, but the workpiece doesn't get hot, check the transistors for heating. If they get excessively hot, your bridge is shooting through.
If all is well at low powers, you are ready for a high-power test. Use your favorite DC source (single phase, three-phase, smoothed, unsmoothed, etc - it doesn't really matter) to power the bridge. Preferably, use a Variac, in case it draws too much current (you can predict current draw from the low-power tests by noting that the heater is a fairly linear load). Don't forget water cooling!
At a few kilowatts, without a crucible, you can melt aluminum and copper and make steel orange-hot. 10 KW+ (50A dryer/stove line or 3-phase) is necessary to melt steel in open air. A crucible helps a lot.
You can control power by very slightly detuning the inverter, or by changing the bus voltage, or by tapping the matching transformer. The latter is a recommended feature, and steel and copper have very different effective "resistances".
Good luck, and have fun!

Step 8: Sources for components

By popular demand, I've added this page.

For the power components, one word - EBAY.
EBAY EBAY EBAY. There is no way this project could have been remotely affordable without it. For the IGBT's, the most reliable source is CTR Surplus, who goes by the usernames ctr_surplus, deals_ctrsurplus, and lisa_ctrsurplus. CTR Surplus also has a constant supply of large electrolytic capacitors, snubbers, and heatsinks used in this project.
The capacitors are also from CTR Surplus - a search for "Eurofarad" works wonders.
Copper tubing is best purchased from Home Depot (assuming you live in the US). They have prices that beat most Internet sources.
The toroids can be from Magnetics, Inc or TSC Ferrite International.
Miscellaneous small components can be purchased from Digi-key.
Arrow has very good prices on transistors, far lower than most other suppliers.

Submitted by MITERS for the Instructables Sponsorship Program

<p>How much steel can I melt say if i make a crucible for it and keep all the heat in can I melt 40kg of steel</p>
<p>not with 30kVA. Maybe 10kg and that takes some doing like vacuum insulation (impractically expensive as the ceramic material has to hold a vacuum as well as withstand 3000F). For 40kg might as well stick to an acetylene-fueled kiln.</p>
<p>Im thinking if i skipped the rectifier in this, could i power the bridge directly with a 3 phase, 400V stick welder with some unknown DC output at 150A. ??</p>
<p>Here are the photos of what i have done.</p>
<p>hi</p><p>I need some one make for me induction heater. i want to heat pipe 10 inch diameter, if u can do it send me mail <a href="mailto:bbtec3d@gmail.com" rel="nofollow">bbtec3d@gmail.com</a>. if it ok may i will buy from u hundreds</p>
<p>l making induction heating now</p><p>I send photo pictur yourself</p>
<p>I need some one make for me induction heater. i want to heat pipe 10 inch diameter, if u can do it send me mail <a href="mailto:bbtec3d@gmail.com" rel="nofollow">bbtec3d@gmail.com</a>. if it ok may i will buy from him hundreds</p>
<p>I need some one make for me induction heater. i want to heat pipe 10 inch diameter, any one can do it send me mail <a href="mailto:bbtec3d@gmail.com" rel="nofollow">bbtec3d@gmail.com</a>. if it ok i will buy from him hundreds</p>
<p>I need some one make for me induction heater. i want to heat pipe 10 inch diameter </p>
<p>How much steel ca you melt with this if you use a 10 kw furnace</p>
<p>Another important point the pcd layout and the actual one constructed in step 4 are different to the circuit diagram in step 3 don't go off the crcit diagram</p>
<p>Thats fascinating</p>
<p>Thats trendy<br></p>
<p>Its fantastic</p>
<p>Thats cooler...</p>
<p>Here is the waveform when is comming out of the ucc37322 before it goes into the toroid. Also i used an arduino as a PWM generator there is a photo of it below here is the code</p><p>void setup()</p><p>{</p><p> pinMode(8, OUTPUT);</p><p>;</p><p>}</p><p>void loop()</p><p>{</p><p> digitalWrite(8, HIGH);</p><p> digitalWrite(8, LOW);</p><p>}</p>
<p>I found out a few things since my last post. The first thing was that the PCB Layout was incorrect on the oscillator PCB. On the ucc37322 the pins 2 and 3 should be connected together or the bottom one connected to 5 volts.Also the little ucc37322 chips short out really easily don't connect the oscilloscope all the time without thinking also don't connect the oscilloscope when the first PCB is connected to the second PCB through the toroid. Check the wave form coming out of the ucc37322. you should only check this when the toroid is not connected though or on the seondary coil when the second PCB is not connected. the image below is the waveform coming out of the second PCB with the mosfets. (also with the toroid i used one out of a microwave the other one i bought from JAYCAR did not work at all the wave form of that one was really bad and not square at all. (this is before it is connected into the second PCB.))</p>
<p>I took 5 Wires of Cat 5 and wound them around the toroid (ferrute Core) od 35 mm ID 20mm 13mm thickness.I have wound the wire round 15 times and all the wires are twisted together i did this with a drill. I put 15 volts into the circut and Just get noise out.</p>
<p>After building the first PCB It appears that it does not work i have connected an ossisliscope up to it and all i get is noise. I am not sure it is a real circut. </p>
<p>Another important point the pcd layout and the actual one constructed in step 4 are different to the circuit diagram in step 3 don't go off the crcit diagram</p>
<p>Now i have drilled the holes using a 1mm drill bit</p>
<p>I am currently building this project. an easy way to make the circuit board is easy to make if you put it on a pdf. I attached it am made it to scale. I then printed it on press and peel transfer paper and etched it using an eching compound the instructions are on the attached image of how to do that. I bought all of the parts Bayley said to buy. </p>
<p>Great project, can you please send me the schematic drawing. </p><p>thanks, </p>
<p>Thats superb...</p>
<p>this is really cool, if you had a chance could you upload a basic circuit diagram i want to build a baby version of this to heat nails, any help is greatly appreicated </p>
<p>hello</p><p>This is a great project</p><p>could you explain more about the coupling transformer and send me power schematics and power components connections</p><p>thank you </p><p>soroush_senemar@yahoo.com</p>
<p>Hi,</p><p>I am needing an induction heater to melt stainless for metal casting.</p><p>Will this heater melt stainless in a crucible?</p>
<p>hi, what kind of measuring system would you use to measure the current through the coil? i'm working on a induction heater and I don't know the currents and frequencies that pass through the coil, i'm not sure how to measure them since i believe the currents are about 700-1000 A.</p>
<p>do the ferrite cores have to be that large?, I am having difficulty finding any that big here in the UK</p>
<p>Thanks! They're possibly one of the best made containers of any sort.</p>
<p>Thanks! They're possibly one of the best made containers of any sort.</p>
<p>do the ferrite cores have to be that large?, I am having difficulty finding any that big here in the UK</p>
<p>I bought mine last week from mag-inc. I`m in the US but, they might be able to ship. Seen some one e-bay too. </p><p>http://www.mag-inc.com/company/news/new-4-inch--kool-mu-toroid</p>
<p>This is the best work I have seen, thanks for sharing. Given the one picture however I wonder if your getting 30kva. Can we see more results somewhere? I understand a much lower frequency would be better for melting, what changes might that require? Thanks, Ben</p>
<p>I've got a counter top induction range that I'd like to reverse engineer into something like this, can I use the same schemata?</p>
<p>hi my friend i want buy you this is induction system how much?</p>
<p>I've got a counter top induction range that I'd like to reverse engineer into something like this, can I use the same schemata?</p>
<p>this link will give you a bigger schematic</p><p>http://www.instructables.com/file/F20WZQPGQBCHZIY/?size=ORIGINAL</p>
<p>have noticed that the photo of the inside of the case the tank coil is multi tapped and there is a toroid by the tank cap that I can see no mention of and the schematic has mosfets whilst the rest of this says IGBTs for stage 2</p>
<p>I've got a counter top induction range that I'd like to reverse engineer into something like this, can I use the same schemata?</p>
<p>I have purchased and assembled all of the components as illustrated. The only thing I am having difficulty with are the two small ferrite inductors. Can you please send me the schematics for these?</p><p>Thank you.</p>
<p>Have a look at this: </p><p><a href="http://wiki.4hv.org/index.php/Gate_drive_transformer" rel="nofollow">http://wiki.4hv.org/index.php/Gate_drive_transform...</a></p><p>Good explaination about using a toroid as a gate drive TXer. It's important info about making this instructable since without it you are likely to lose a couple hundred dollars blowing you IGBT if done wrong. I personally think naming specific toroid types would have been proper for &quot;instruction&quot;. I would start with something like : FT-150-J. Maybe bigger and fairly thick. That is a ferrite 1.5 inch O.D. </p><p>Wrap it tight, place it near the transistors as he has pictured. That is important. In the schematic he has a series resistor in the first gate drive board so you should not have to place one of your own. </p><p> You should not have to wrap more that 15 turns to get the proper signal transfer. No less than 9 turns. That is the &quot;grey area&quot;. Too many wraps and it's bad. Too few and it's bad. He hints to 10 windings and that is a good starting place. Trial and error here without a scope could be frustrating. If you try it without one, monitor those IGBT and transistors with low bus voltage for a while to see how hot they get. I would use a variac and no more than 40 volts if it sucks less than 10 amps and adjust for max current draw with the inverter. If it can't handle that you will probably have a little explosion at 240 volts. </p>
<p>About the 2 ferrite coils, my 2 cents.</p><p>Since these are basically isolation TX's, and from the hints from how bwang comments and the pictures, I believe he is using CAT5 cable which has 5 sets of 2 twisted wires. And that would be better to have each winding twisted tightly so it makes sense since they come that way.</p><p> And I would assume that he is using ferrite only and not iron cores that are of the material best made for the frequency they operate. That would be, I think, FT-xx- J or 77 type cores. You probably can not just use any core since some types of materials will actually &quot;choke&quot; signals at certain frequencies. So you should have the right ferrite to begin with.</p><p>Now with lack of detailed info I can only offer help to windings. I would assume that they are 1:1, meaning the primary will have the same amount of windings as the secondaries. It could be a bit more or less. It would be nice to know more about how he did it and I wish to have seen that in more detail. </p><p> So I would take the 5 pairs of twisted wires from the CAT5 cable and wind them around the toroid coil about 10 times. Choose one of those 5 pairs and put it to the driver, and the other 4 to the transistors as in the schematic. This is where having an oscilloscope would be handy as well as more info because of the trial and error. You are transferring the square wave signal from the drivers to the transistors. The signal needs to be clean. The wrong coil can cause no function to ringing. </p><p> I could be wrong and the windings could be a lesser or more ratio. But it would not be much, on order of . 2 in difference. He might have even wound the 4 pairs of wires first then would the primary over them. I don't know. </p><p> If you ever read this bwang, please tell us what core materials you ended up using. It appears you at least tried one other coil that did not end up being in your final pic. And info about the windings@! </p><p>Hope this helps. </p>
<p>Bwang, Thank you for the great build. After mulling over your project I have a few questions and considerations. </p><p> You explain in short many of the aspects to this project but there are a few details that beginners might not be able to understand and are hard to deduce from the text. May I suggest more detail about winding the toroid cores for gate drives. I think it is confusing. I am sure you left it a little vague becuase they are areas where a bit if trial and error are needed to tune it just right and depends on the core itself. And just to be sure you used strictly ferrites and not powder iron ferrites for the gate drive TXs?</p><p> Also I think pointing out the use of ferrite for the main coupling transformer. I have seen builds using type 3 iron cores work but they got warm. Toroids are confusing to newer persons that might want to attempt this. </p><p> The schematic is useful but I found differences in it and you pics. The potentiometers are interchanged on the schematic from what is shows later. I think it was the 20k and 50k. And it looks like you used a 10 turn for the pot your mounted control. Just to be clear, which one did you mount on the board and which one on the chassis? </p><p> Last thing of question would be layout. Have you experienced any funky signals from placement? I see you mounted (glued), yours very close to the chassis. Was that needed becuase you got bad signals? </p><p>I hope you can chuck in a comment back to this. I am sure there are many persons who would appreciate it. </p><p> Thanks!</p>
<p>please, can someone tell me how to wind the &quot;gate drive transformers&quot; to get 8 terminals to drive the mosfet and the IGBT.</p>
<p>Great project, can you please send me the schematic drawing.</p>

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