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>But i asked in a place on the internet that sells induction furnaces from 10 to 100+ KW and he says that with 15KW you can melt 40kg of steel but it takes longer obviously i am gonna make a good crucible for insulating, but is there anyway i can turn this into a say 30KW and what about acetylene fueled kiln whats that is that like propane and forced air can i melt 40kg of steel with that or do, whats the difference between propane and acetylene</p>
<p>The internet lies.... regularly.... please fact check. And Punctuate....PLEASE!</p><p>Acetylene: <a href="https://en.wikipedia.org/wiki/Acetylene." rel="nofollow">https://en.wikipedia.org/wiki/Acetylene.</a></p><p>10kw vs 100kw will be very different... both in construction and price tag.</p><p>40 kg is roughly 88 lbs. You're basically melting a large German Shepherd or a reasonably fit 5th grader... That much VOLUME is going to need a VERY large crucible...a cylinder roughly 6&quot; in Diameter by 10&quot; tall...ish... not quite 3 gallons of molten steel....(http://www.aqua-calc.com/calculate/volume-to-weigh...</p><p>I've never seen a crucible that big for sale...</p><p> and that Crucible will need industrial grade insulation...Think: Aerogel. Quantity+Performance=Cost....</p><p>The setup can scale bigger, but most homes won't have the facilities necessary for handling any larger amperage, without some modding of the main distribution panel... (and a $1k+ permit)</p><p>I think you may need to examine a more cost effective method for handling that much steel. consider multiple melts?</p><p>What's the underlying purpose? why does it have to be 40kg? does it all need to be liquid at once? perhaps pre-purchasing materials and fabricating via fasteners may be your best bet....?</p>
<p>40 kg is roughly 88 lbs. You're basically melting a large German Shepherd or a reasonably fit 5th grader HAHAHAHAHAHAHAHAHAH :) <br>well I can make my own crucible but for the power source IDK <br>yes 40 kg because I want to make my own anvils and weight plates but say in one batch to make 4 10kg ETC you get the point <br>but how much is 30KVA in KW</p>
<p>Please Punctuate. Use Periods and Commas and things.... It is quite difficult to read your comments without them...</p><p>Honestly, &quot;but say in one batch to make 4 10kg ETC you get the point&quot;....actually, I don't... are you saying that you may not need to do all of it at once, or that you DO have to do all of it at once? please be concise...</p><p>&quot;well I can make my own crucible but for the power source IDK&quot; Can you, now? Please, enlighten me. I don't know where I could even source the materials for building such a behemoth... or even how I would lift it... with 88 lbs of molten steel in a massive crucible made of very dense material... can you lift 150-ish lbs with your arms straight out, and pour it with control? I sure can't...</p><p>anvils don't have to be 88 lbs... mine's 40 lbs, and it does just fine for my smithing... many are smaller. consider a smaller anvil...Especially as a first time casting. in fact, don't do an anvil at all right off the bat. try casting a cube, or a cylinder, or even a small muffin shape. additionally, You're not just talking about any steel... You mean hardenable tool steel... that changes the game significantly. this makes everything beefier. and harder to melt.<br></p><p>Finally, WAY before starting anything this ambitious, try looking around for the info first. It's very difficult to explain technical topics to someone with very little knowledge of it.</p><p><a href="http://lmgtfy.com/?q=convert+30+Kva+to+Kw" rel="nofollow">http://lmgtfy.com/?q=convert+30+Kva+to+Kw</a></p><p>Don't ask what a power factor is. Look first, and ask questions to things you still don't know.</p>
<p>lol I know right, sounds like a Tim-The-Toolman disaster in the making. I hope he videos it in case he accidently pours molten steel on himself (assuming he doesn't electrocute himself before that or dies from exploding IGBT shrapnel in the eye), would make a nice video for Bestgore.</p>
<p>Meh screw the $1k permit and stupid expensive union labor that entails. I simply pulled out my main 100A breaker and dropped in a 200A for less than $50 (the cost of the 200A breaker on ebay) since my annual Section 8 recertification doesn't bother checking the electrical panel (I'm going to assume after initial insurance inspection it's the same with everyone else). The pole transformer will not explode, it's rated 25kVA but can easily do 2-3x that for a few hours at a time (with about 10% voltage drop). The cables get warm but I doubt they will melt as long as it's not running for hours on end. If was worried about fires I'd get fire insurance.</p>
<p>How about to heat a 3&quot; dia bolt that is 2' long and has a 21mm dia hole through the center of it? The entire length would need to be heated to roughly 350F to make the bolt stretch. I'm thinking you would need a minimum of 35kva. I am looking for a unit that is self-contained (internally cooled). Is this something that you think you could make?</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>

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