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Introduction

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.


WARNINGS

  • 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.
Hi, I want to make this project. You can send me its schematic to this email : shivana.5511@yahoo.com<br>
<p>Hello,</p><p>I was wondering why the ferrite toroids for the coupling transformer are so large?! Wouldn't it be better to have toroids with a smaller diameter to reduce magnetic losses?!</p>
<p>Magnetic losses occur more with smaller toroids because magnetic saturation occurs faster with a smaller amount of iron</p>
Ok, it makes sense...thank you for your reply.
<p>anytime</p>
<p>By the way, I would have another question if you don't mind...maybe you have an idea.<br>I saw a comment from lavila540 on this page who ordered the following ferrite cores for his induction heater:</p><p><a href="http://www.mag-inc.com/company/news/new-4-inch--kool-mu-toroid" rel="nofollow">http://www.mag-inc.com/company/news/new-4-inch--ko...</a></p><p>But I would aim for those cores (with the P material):</p><p><a href="http://www.mag-inc.com/home/Advanced-Search-Results?pn=49725" rel="nofollow">http://www.mag-inc.com/home/Advanced-Search-Result...</a></p><p>where the inductance and permeability are much higher. But in the first case they call it the &quot;Kool Mu Permeability&quot;...so is there a difference with a &quot;normal permeability&quot;?! I am a bit confused...<br>What would be the most important characteristics to look at?<br><br>Thanks</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>Hello lavila540,<br>Have you finished your induction heater? Does it work well?<br>I was wondering why you chose these ferrite cores? Is it working well with these ones (no heating)? What is the most important characteristics to look at?<br>Do you think these ferrite cores might work as well:</p><p><a href="http://www.mag-inc.com/home/Advanced-Search-Results?pn=49725" rel="nofollow">http://www.mag-inc.com/home/Advanced-Search-Result...</a></p><p>I'm aiming for the P material. But comparing yours and these ones, the permeability and the inductance are much different...I am confused...<br></p>
<p>Greetings,</p><p>Is it possible to get the schematics emailed.</p><p>jeff@fd-intl.com</p><p>Thanks</p>
<p>If possible, I would like receive schematic diagramms by my e-mail.</p><p>FYR, e-mai address is <a href="mailto:franzhwang@hanmail.net" rel="nofollow">franzhwang@hanmail.net</a></p><p>Thanks</p>
<p>i want document. you can send me? please...</p><p>sarawut262535@gmail.com</p>
Where is your scmatic? <br>I want to build a very small one
<p>hello </p><p>need to circuit diagram to progect </p>30 kVA Induction Heater
<p>what is the current going into the tank? The capacitors I have found by Eurofarad have been rated around 150 amps max. After the current is stepped up by the coupling transformer won't the current exceed this?</p>
<p>Not sure if you know, but if not then your work has been stolen:<br><a href="http://ofslides.com/bwang-546040/presentation-1019981">Check here</a><br>Brooklytonia found the website and opened a thread about it in the forum as well.<br>However, if that is something you published there yourself forget about it ;)</p>
<p>I'm wrong-1,800,000 VAR=1,800KVAR.If I'm getting 400 amps to the work head than the tank circuit should have unreal current in it,I can't even calculate it!</p>
<p>My system will be operating at 30khz with 1.92 microhenry work coil with 1/2&quot; tubing I believe I will sweat 56% Silver solder onto .This F0 will not over drive the IGBT's and create great penetration.I Should have many thousands of amps in work coil with Q of 126 icrease in input tank current.</p>
<p>I'm building my system around 4 600 amp Powerex's and BG1A gate drivers.I have a 16 tap 800KVAR workhead.My main tank capacitor is 15uf at 6kv,300amp oil filled capacitor rated at 1,800,000KVAR,weighs about 30 pounds! I am driving the inverter with a 130 vdc at 400 amp military grage generator and a 60 hp Suzuki samari engine.This gives me This gives me 52,000 or 52 kiolwatts of power to work with.This should defiately smelt a little steel?</p>
<p>Okay, bare with me because electronics is far from my field of expertise, and I have a few questions I'm hoping someone can help answer. </p><p>First, why is it necessary to have a rectifier (its not really mentioned) if we are just going to reconvert the signal back to AC? I'm guessing that a DC source is needed for the input to the IC which is the oscillator which then drives the gate drives, the power stage and eventually the tank circuit. That being said it also appears that the rectifier is wired directly into the IGBTs, is it necessary to use DC to drive these? Am I on the right path with any of this? </p><p>Second, it's stated that the the frequency and dead time of the oscillator can be controlled, but how exactly? How is the frequency of the AC current in the tank circuit actually controlled? </p><p>Lastly, what is the function of the input capacitor and why is it necessary? There's no mention of it other than in the picture at the beginning. </p><p>If anyone could take the time to explain these things to me I would really appreciate it. </p>
<p>Going another direction, I want to anneal brass tubing. I'm *trying* to build something that will heat rifle cases to around 750*F. without over annealing them, and do it in a very short period of time so I can maintain production volume.</p><p>This takes a coil that is open enough for the brass to enter on a belt/conveyor and exit the same way, so the coil is longer, oval with the ends bent up to allow for brass to pass into the induction coil, and out of the induction coil as it proceeds down the production line.</p><p>I CAN regulate the belt speed through the coils... And I can get the coils very close to the brass, but what I'm having an issue with is the amount of brass moving on the line (Mass) and building an inductor with enough power to make the brass reach the designated 750*F.</p><p>With rifle brass, It's a pretty good conductor, so it doesn't heat as fast as steel, and I'm not trying to anneal the entire brass, just the top 3/4&quot; or so... But production still puts a lot of brass in the coils at one time, so the heating is VERY slow, which leads to thermal transfer down into the case body/bottom, which I DO NOT want. I would rather the sides/bottom stayed under 450*F.</p><p>I'm considering a water bath for the bottom of the cases, which is going to add more mass and slow the induction heating of the top of the brass...</p><p>Since this is for a high volume competition shooter (100K rounds/year), and not a business, I would be glad to pay a REASONABLE amount of money for someone that can help address these issues.</p><p>I've seen the high volume MANUFACTURERS have induction heaters that would knock out the entire process in just 3 or 4 seconds, I'm not looking for something that draws 440 volts AC and spins the electric meter off the side of the garage, but I would consider 220 VAC single phase, providing the unit works efficiently and doesn't cost a fortune to build or operate...</p><p>Anyone got any ideas how to build something that doesn't bust the bank?</p>
<p>I'm sorry to disappoint you a little bit, but there's one caveat to your water bath plant: all the copper alloys are not only good electrical conductors, but good heat conductors as well (there's a reason why all the high-quality heatsinks are made either from pure copper or aluminium with a copper core just above the CPU). Thus if you'd add water to any parts of the brass casing, you'd make it even harder for it to heat up to your desired temperature of 750 &deg;F, because water is a VERY good coolant (it has one of the highest heat capacities of all the fluids).</p><p>Since there seem to be no 3-phase electric outlets installed in US homes at all for some strange reason, I'd recommend you obtain some REALLY high amperage outlets for this project (a 100A one would get you reasonably close to the 30 kVA mentioned in the project). Moreover I'd also consider lowering the frequency a tad bit (no more than 10-20 kHz tops), get a bit smaller pipes, wind them in very close loops (while making sure that the loops are adequately insulated from each other e.g. by a lacquer) and wind multiple loops on top of each other (this increases inductance a LOT). All of these things (and probably quite a few others folks more knowledgeable about this topic than me perhaps know about) are just tweaks though: the main issue is that you MUST deliver more energy to your brass cases than necessary for heating them. Frankly if I were you I'd just use some heating elements instead.....</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>Not that I'm aware of. I'm not sure whether there are any welders on the market that could supply 30 kVA of power. Even on 400V (3-phase) level that's 75 amps. On the voltage levels typical for welders (like those 20-40 volts mentioned above) you'd need the welder to supply AT LEAST 750 amps (not accounting for conversion losses of course). It goes without saying that such welders (if they even exist) are ridiculously expensive. So expensive in fact that you'd be better off even commissioning some freelancer (or a local EE student) to build this PLUS paying the whole BoM than buying an appropriate welder that'd supply the required power.</p>
<p>Not really. Welder voltage too low and not stable at all (usually 70 or so volts with no load and 20-40v at that 150A). Sure you can run 350v-400vdc circuits on 35-40vdc but at only 1% the power since then it will also be at 1/10 the current. 300 VA might get a small 1/4-20 screw hot, but why build all this just to do that? That's like buying a Ferarri but never driving over 55mph.</p>
<p>could you send me the schematic? may email: nguyenhuanute</p><p>@gmail.com</p>
<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>Did anyone tell you that you are annoying, you cant just say that someone has no knowledge, because you don't even know them or in this case me and if your that stupid you can read what I wrote because I got my punctuation wrong then your just a snobby little big ego geek that study's all day and night but despite doing that gets nowhere.</p>
<p>Wait, let me look at my map of the internet.</p><p>Ah yes! &quot;Here there be trolls&quot; Gotcha.</p><p>That's all folks!</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>Power utility: &quot;don't do that&quot;</p><p>Hopefully they aren't oil filled; they will explode eventually.</p>
<p>Pole transformers are insanely over-engineered since they are designed to handle switching spikes and voltage transients from thunderstorms and run at the full spec plate rating with only 1-2% loss 24/7 for 30-50 years. For 1 min runs they can do 10x their rating and only get warm. I know, there's a few Youtube videos of a guy running a 3 kVA one on a 150A circuit with no ballast at all (36kVA, over 10 amps on the 7200v side with a huge voltage drop) to see if it would blow up and it didn't. Now if he allowed that to continue for an hour yeah it would probably boil the oil and shoot the lid off. But that's when the utility just comes and replaces it with a bigger one.</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>i need complete circuit diagram , help please <br>if someone has simulation file then pls email me saad.sc.saad@gmail.com</p>
<p>I'm just an ME/MSE and want to modify this kit to include capabilities to quickly rotate the casting while running a DC current through the sample. Without digging through all the EE I would like to know if it is possible. Thanks!</p>
<p>I am building this induction heater and i have a problem. In oscilator you have 6R resistor, what value is that?? Thanks</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>Here are the photos of what i have done.</p>

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