Induction Heater - 6" Coil vs. 1/2" bar

  • Published on Jan 7, 2013
  • Updates on this project are being posted on the new Patreon page:
    You can also support the future of this project there as well.
    Heating a 6" section of a 1/2" bar. The heater is pulling about 1500 watts when the bar is cold and about 6500 watts once it heats up. Much more efficient than my previous induction heater.
    For details on how to build your own visit:
    ReactorForge Blog:
  • Science & TechnologyScience & Technology

Comments • 321

  • Chris Russell
    Chris Russell 19 days ago

    i miss playing with an industrial unit. it would have vaporised that 1/2" bar in about 2 seconds...

  • creator Space
    creator Space 3 months ago

    We made it well.

  • Vincent Robinette
    Vincent Robinette 8 months ago

    Did you notice a drop in inductance as the iron transitioned from ferromagnetic to paramagnetic as it heated past the curie point?

    • Vincent Robinette
      Vincent Robinette 8 months ago

      @Josh Campbell Exactly. By just measuring the frequency, it can be calculated by the value of the capacitors who's values don't change, even though the impedance changes with frequency.

    • Josh Campbell
      Josh Campbell  8 months ago +1

      @Vincent Robinette I didn't answer your entire question. You asked if I noticed a drop in inductance. The short answer is yes technical, but I'm not reading it out. You could calculate the actual work piece inductance based on the current PSC2 inverter output compare register value. The PSC2 OCR is changed dynamically as the phase difference between the inverter current and the inverter voltage shifts in an attempt to keep the frequency operating at the resonant point (keeps inductive and capacitive reactance equal). Since we know the inverter frequency (because we are setting it) you would just use the series resonance circuit formula and solve for L.

    • Vincent Robinette
      Vincent Robinette 8 months ago

      @Josh Campbell I understand that, it's the eddy current squared, X the resistance of the metal, that determines how much heat is induced into the workpiece, but I was curious about the change of inductance. The only way to tell, would be to put a frequency counter on the tank circuit capacitors, and look for a sudden change in frequency, as it crosses curie point. It should go up. If you put ferrite in the coil, the frequency should drop. Aluminum or copper, should cause a rise. Hot steel should take on the electrical properties of brass, or bronze. Iron is a poor conductor compared to other non ferrous metals.

    • Josh Campbell
      Josh Campbell  8 months ago +1

      Yes, you can tell when it crosses the curie point but heating doesn't slow down. In fact, it speeds up (gets easier) since the resistance of the workpiece rises with temperature.

  • Nawras Alil
    Nawras Alil 10 months ago

    how i could make the copper heated like this iron stick in the same this cuircut?

    • Josh Campbell
      Josh Campbell  10 months ago

      Using the same setup, I have successfully heated copper as well. I used a smaller coil to get a higher resonant frequency and used it to braze other coils! :)

  • Adanqasim Qasim
    Adanqasim Qasim 11 months ago

    Hi Dr farind how are you
    This in Pakistan Delivery mechanics ho Mac prieszy
    My watsyb 00966592673439

  • William Alexander
    William Alexander 11 months ago

    What is the largest Loop size you could make the coil before heating became impossible or the magnetic field was negligible?
    (Size Ratio of Loops to object passing thru loops)
    I don't know if I'm asking this right..

  • The Last Stylebender
    The Last Stylebender 11 months ago +1

    Please teach me how to build something simple to heat my small swimming pool bro.

    • Josh Campbell
      Josh Campbell  10 months ago

      You could make a simple low-cost solar-type like this:
      I wouldn't recommend hooking up an induction heater to your pool! ;)

  • Andys WroughtIron

    Can i just buy one from you? Great job man

    • Josh Campbell
      Josh Campbell  Year ago

      Absolutely, and thank you for the follow!@Andys WroughtIron

    • Andys WroughtIron
      Andys WroughtIron Year ago

      Just realized you had a patreon. Following now

    • Andys WroughtIron
      Andys WroughtIron Year ago

      Thank you. Let us know when its ready this would me so much.

    • Josh Campbell
      Josh Campbell  Year ago +1

      Almost, I'm working on it! I have the web store setup and running with a few essential items. I'm working on refining the other systems and getting them listed as well as sourcing some of the other vital components now. :)

  • Dr. john villegas

    necesito fabricar uno para 6 inches ratio

  • Sean Fagan
    Sean Fagan Year ago

    What's crazy is if you put your clock inside their it would still be cold.

  • Indigo Dragon71
    Indigo Dragon71 Year ago

    Why not use a graphite rod instead of an iron rod? Then enclose the induction coil in a thin sleave of titainum to cause titanium to glow white hot? You could use much lower voltage to generate heat and even better idea would be to line a insulated cylinder with nintinol thermal electric generators with the titainum sleave being positioned directly in the middle with air being forced around it to heat the air. The Nintinol thermal electric generators could then generate the volts needed to operate the electronics to operate the the induction and the electric fan to draw in air through the insulated cylinder. A space heater you can plug in to a wall socket or 12 volt plug or clip to a 12 volt battery to start it up then the space heater becomes self sustaining after Nintinol thermal electric generators kick in. Then you would have a self powering space heater you could use in a tent a camper or trailer or shelter without any fears of generating toxic fumes. 😊

  • Eslam Kaled
    Eslam Kaled Year ago

    Please send your e-mail address

  • Shanta Hsieh
    Shanta Hsieh Year ago

    I took great plans from Avasva . It help me a lot with my own solars.

  • La Boîte Du Web
    La Boîte Du Web Year ago

    Hello I'm French and I would like to make an induction heater. I'm looking for plans and schematics for your heater but on your website there is no information available. Where to find it? Thanks a lot

  • Stylemilitar Comandos

    I want to be as smart as you and do the same invention in my hands but I do not know what things you use the truth

  • FreeFlamingInfinite
    FreeFlamingInfinite Year ago +1

    Soooo... 26A at 800V p-to-p?
    You sure you got that voltage right?
    Surely you're not running at 10.4KW?

    • FreeFlamingInfinite
      FreeFlamingInfinite Year ago

      Great answer! Thanks for the clarification. Makes sense now, and an efficiency of 95% is extremely impressive to say the least! I have heard rumors of the sneaky power tactics implemented by most companies especially when it comes to sound equipment, but now I see just how sneaky they're being.
      Thanks again!

    • Josh Campbell
      Josh Campbell  Year ago +2

      Great question! The 800 Vpp measurement is across the capacitor in the tank circuit. To calculate input power what we need to look at is the input voltage and current. So 240VAC at 26A = 6,240 watts of total input power. And since it runs at a power factor near 1, the reactive power is near 0 making 6KW the true input power. (KW = KVA, look up the beer analogy for reactive power)
      Extra (continuing with the beer analogy):
      To get a DC voltage for the inverter, induction heaters and similar machines must rectify the incoming AC voltage. Add filtering to this rectification and you lower the power factor to a point where only about 60% of the total reactive power (KVA) is doing real work (KW). Most companies take the reactive power (KVAR) and add it to the real work power (KW) then display the reactive power or KVA as the machines total power. This number one of the measurement you often see on the front of an induction heater, in its part number, or plastered on its eBay listing. It is NOT the portion of power doing real work or heating power of the unit but the full reactive power. A good rule of thumb, if you see a 15KW induction heater on eBay you should probably calculate for a power factor of 0.6 meaning only 60% of that 15KW is doing real work. So.... 15KVA x 40% leaves 9KW after removing 6KVAR. Pretty sneaky but nothing new.
      The reactor forge uses stronger components and a different type of filtering raising the power factor to around 0.96 to 0.99. This means that nearly 100% of the input power is doing real work. When the machine is running at resonance it is extremely efficient and about 95% of the power makes it into the work piece. This is pretty stinking significant especially if you compare it to heating metal with a flame. Consider for a moment how much of a fuels energy makes it into the work piece when burning it and transferring that energy through convection... Hint: you would almost invert that 95%, crazy!

      No, it's running at 6.2KW.

  • Tim O'Brien
    Tim O'Brien Year ago

    Is the Induction Coil solid copper?

  • Paco Bosch
    Paco Bosch Year ago


  • Eric
    Eric Year ago

    By resonant frequency, you mean the frequency to most excite the atoms in the material? I'm assuming it changes with temperature?

  • FIREHAWK1979
    FIREHAWK1979 Year ago

    You could heat up a section of steam pipe with water vapour sprayed into it to make a rocket, or desalination still.

  • Selim Pul
    Selim Pul Year ago

    What is the cheapest and easy way to make induction heater to heat 16 mm diameter steel bar? Thanks..

    • Selim Pul
      Selim Pul Year ago

      Josh Campbell thank you for your detailed explanation josh. I will be on it.

    • Josh Campbell
      Josh Campbell  Year ago

      The cheapest way to make one? Start with a DIY controller using a low-cost microprocessor to generate the PWM pulses for the inverter, no display no input other than a start button. When the switch is pressed ramp down the frequency from the maximum, your inverter can handle until resonance in the tank circuit occurs. This can be determined by a variety of methods. Use the PWM signals generated by your controller to drive high-speed switches such as IGBTs or MOSFETs, this is your inverter. The inverter drives an impedance matching transformer. Make the transformer out of toroidal cores or whatever ferrite material you can get your hands on, just make sure it is a material type that can handle frequencies in the kHz range and power levels in the kW range. Make your tank out of eBay surplus high voltage & current capacitors with copper tubing to connect it all. Pump water through all of the tube to cool it. Use a pond pump or a salvaged windshield wiper pump. Be careful with water and high voltage! If you would like more detail, then ask more detailed questions. ;) I'm working on guides to explain all of this in MUCH greater depth with photos and models.

  • Josh Campbell
    Josh Campbell  2 years ago +1

    Apparently, I sell induction heaters out of this company in India... nice! (notice the image is taken from this video)

  • meshugunner
    meshugunner 2 years ago

    I assume this is now defunct since the links don't work and there is no schematic out at Github

    • Josh Campbell
      Josh Campbell  2 years ago

      Also, I'll be using the Patreon page for updates that don't fit into the Github style (social etc.).

    • Josh Campbell
      Josh Campbell  2 years ago

      I understand, there is a lot on git hub. The Wiki (tab) will help explain the what and as far as the where well you just need to navigate the directory structure under the Code (tab). Schematics would be under hardware. I'm working on getting the new schematics and code for the CriticalMass Core on there but the older stuff is there now.
      And yes there is a tank circuit, but no the current machine drive the tank with IGBTs and a power stage controller to generate the signaling and control the resonant frequency. The old machine used a PLL to generate signaling and lock onto Fr.

    • meshugunner
      meshugunner 2 years ago

      Thanks Josh. I"m afraid I find that site confusing. Where do I find a schematic? I assume you have a tank circuit powered by big mosfets and some switching source to drive the gates?

    • Josh Campbell
      Josh Campbell  2 years ago +1

      I've updated the link and have actually been working on this recently. Finally! ;)

  • Setyawan Tulus Raharjo Saminista 67

    pemanas itu pantas diterapkan pada mesin penekan batang baja untuk pembuatan bola besi

    • Josh Campbell
      Josh Campbell  2 years ago

      Ya, itu salah satu kemungkinan penggunaannya.

  • Ciobanu George
    Ciobanu George 2 years ago

    LIKE! I have no knowledge of electric or electronic parts.. Please, tell me how much will costs to build something like this? Thank you in advance.

    • Josh Campbell
      Josh Campbell  2 years ago

      This could be a pretty dangerous project for a beginner so I would work on that part first. The raw material cost for "something like this" can vary wildly. Some throw together a working version for less than a hundred bucks, this one setting on a desk top with no case, extras, controls or display is about $4-500. Not counting supporting items like an oscilloscope, auto transformer, programers, etc... Understanding electrics and then the circuit will get you the answer to that question.

  • FixItStupid
    FixItStupid 2 years ago +1

    Nice Work

  • Robert Applegate
    Robert Applegate 2 years ago

    Be careful to keep that thing off the international emergency frequency or you're going to have an experience that you won't like!

  • MAXTIL 2016
    MAXTIL 2016 2 years ago


  • Eren Saygı
    Eren Saygı 2 years ago

    Verry nice
    I also tried that type of ind. heater but it didnt work very vell, i got
    some coupling issue, maybe I miss something about it, I would like to
    buy your circuit plan if you say ok ???

    • Josh Campbell
      Josh Campbell  2 years ago

      I've been extremely busy but I will get it up here eventually.

  • Parallax
    Parallax 2 years ago

    Would make a cool looking but unsafe light fixture

  • Rookie
    Rookie 2 years ago +1

    Its my first time knowing what an induction heater and i have a few questions about it.
    1.Does it burn your hand if you touch the outside of it?
    2.How hot can the metal get? much voltage or amps does it use?

    • Rookie
      Rookie 2 years ago +1

      Thanks! This helps alot!

    • Josh Campbell
      Josh Campbell  2 years ago

      1. No but don't touch it.
      2. The IH generates electric currents inside the conductor called eddy currents, those currents cause resistive heating. Also magnetic hysteresis adds a small amount of heating to magnetic metals below their curie temperature.
      3. This one, 240V up to 60A but I limit it to 30-40A range with short spikes into the 50's.

  • Alexis Carrel
    Alexis Carrel 2 years ago


  • Boost - Nova
    Boost - Nova 2 years ago

    This man here is a genius!!! Take my money!!!

  • Metal Rott
    Metal Rott 2 years ago

    I'd like to build one like that with a little more power to make killer knives.

    • Andy LEE
      Andy LEE 2 years ago

      I am an expert in induction heating industry,
      Please write to me, your detailed request, i will help you!
      Whatsapp No.: +86 131 1368 8127
      Pls add my Skype ID: andrew6682527
      QQ: 2996496980
      We can chat online!
      Any comments, that'll be appreciated!

  • Beautiful Mind
    Beautiful Mind 2 years ago

    how much amps?

  • Mahendra Kumar Pallapothu

    How can I contact you for a project concept. Please let me know your email/

  • Becky liu
    Becky liu 2 years ago

    Will u add me as your wechat friend qq3001096024



    • GunFun ZS
      GunFun ZS 2 years ago

      If you look in the 'about' section above he has links to the project plans. PS, typing in capslocks with a request is considered impolite. It's equivalent to Shouting AT a Stranger with a demand.

  • Fabiano Sansoni
    Fabiano Sansoni 2 years ago

    hello, you can share the project diagrams, thanks

  • mediaguardian
    mediaguardian 3 years ago

    Why are home made induction heaters so slow to heat up the metal? Even the most elaborate setups are slow. I have seen them in manufacturing systems where they heat up a 1/2" steel rod almost instantly.

    • GunFun ZS
      GunFun ZS 2 years ago

      Wattage and focus. This is spread over a large area with a lot of thermal mass. The systems you are talkning about are liquid cooled so they can handle a lot of wattage and are focussed to rapidly heat only a small area of the bar before the rest is able to heat sink away the energy.

  • Advanced Nutrition Inc

    Josh, Great Work !! ... I see you have taken a lot of attention to detail, water cooled coil, serious cooling for your drive board. Why do you need so much circuity to create the drive wave? I see a sine wave and a square wave. I would guess the square wave is the main drive wave outside the tank circuit and the sine wave is whats generated inside the tank circuit once you have tuned it properly. I see you have at least 3 circuit modules. I assume you are able to modify each part of the drive signal including frequency. In my mind it seems it could be simpler - what creates the need for so much circuitry? I know you are doing zero crossing detection, etc.

  • Donald Duck
    Donald Duck 3 years ago

    Wirbelströme / eddy currents

  • Zaron DarkStar
    Zaron DarkStar 3 years ago

    I am interested in making an adjustable induction heater like yours, but I have been searching for a good, step-by-step, from the wall socket to the coil video guide on how to set one up. But I am frustrated because I haven't found a good one yet. Everything I have found so far has either been bits and pieces, or just videos of them working, or very small ones. I would love to see a full walk-through of your setup! I am subscribed, and eagerly waiting for a new video!

  • Jim Martin
    Jim Martin 3 years ago

    If so could not a stand alone heater be designed using a capacitor a TEG a fan a electromagnetic pump and a heat exchange coil? Novartis

  • Jim Martin
    Jim Martin 3 years ago

    Could a titanium pipe be heated the same way to heat gallium being circulated through the pipe?

  • Jai Kishsn Koil
    Jai Kishsn Koil 3 years ago

    lathe machine

  • levettp
    levettp 3 years ago


  • Nick Merritt
    Nick Merritt 3 years ago

    Cool video, I had a few questions. So you said the "resonant frequency" changes as the material heats up. Is this referring to the AC frequency, and is there a sweet spot for energy transfer efficiency for any given material? Also, why does the inductor draw more current throughout the process? Thanks!

    • nathaniel newman
      nathaniel newman 3 years ago +1

      Same power and higher frequency:
      Think of it as this: you poura gallon of water every minute to fill a bathtub with the drain open, the frequency is that gallon of water.
      As the molecules heat the frequency increases, so you have to pour faster to keep the water from draining from the tub. that heat isn't free...
      The heat is a factor of the mechanical loss of electricity through the conductor.
      As the water gets warmer, the tub requires more water per minute to fill...
      Maybe a beter analogy is Gelatin as you can see the density change. If it is cold it is slow and as it heats up it moves faster, so you need to pour more gelatin through a funnel to keep it at the same level. that is the physics behind higher current to keep an already hot element hot compared to a unit that is at a lower heat, that is why computers should be cold, not hot!
      once it gets hot it gets super inefficient.

    PAULO BARBOSA Vagal 3 years ago

    vende cuanto custa responde

  • Lemonschooner
    Lemonschooner 3 years ago

    Could you theoretically use something like this for blacksmithing, or would it be better to stick to traditional methods of heating the metal?

    • Corpus Crewman
      Corpus Crewman 3 years ago

      @Lemonschooner The way that the knife is passed through the coil causes some parts to become heated and some parts stay unheated. thus causing an uneven heating.

    • Lemonschooner
      Lemonschooner 3 years ago

      Hm. What is it about this method that creates uneven heat? Something to do with the design of the coil (like the spaces in between loops) or something inherent to the way the metal is heated?

    • Corpus Crewman
      Corpus Crewman 3 years ago

      You could definitely use this for smithing, but a normal charcoal furnace is better for a more even heat and therefore greater steel integrity.

  • Fernando Reynoso
    Fernando Reynoso 3 years ago

    Boring : (

    NITESCIENTIST 3 years ago

    nice workstation.

  • Jose Bueno
    Jose Bueno 3 years ago

    Hydrogen engine

  • John Conrad
    John Conrad 3 years ago

    why did you not show the complete setup? just to show that induction heating works?

  • ExploitCode
    ExploitCode 3 years ago

    What if you put finger in?

  • Nick Mariani
    Nick Mariani 3 years ago

    Great build, I'm wondering how much that celem cap cost you and what the capacitance value is? Also, where did you order from?

    • Andy LEE
      Andy LEE 7 months ago

      i will answer your questions , you can add my whatsapp +8613113688127 ,i will tell your more details,

  • Krause Sciens
    Krause Sciens 3 years ago

    Question: Is the resonant frequency increasing or decreasing when it starts to heat. I am assuming an increase, as it would take more energy to heat the material hotter and hotter.
    Question 2: What was the range in frequency change across the heat range visible in that video? Like, how much frequency adjustment occurred for you to hit the resonant frequency from room temp to when you tuned past the resonant frequency?

  • ahmed mohamad
    ahmed mohamad 3 years ago

    hey this is awesome man can i build one to melt metal and how can i make the frequency goes up to KHZ

  • Artistic Diyer
    Artistic Diyer 3 years ago +4

    very good video, i brought a 1000 watt Induction Heater for Harding home made tools works good

    • Joao Ferreira
      Joao Ferreira 3 years ago +1

      I think your induction board is similar to this one you can see in this link: sending attached, isn't it? (sorry about link but I don't know how to attach an image here)
      Your information about the transformer is very, very important.
      I want to buy one of these boards to weld (brazing) in small pieces of mild steel. The solder melts at temperatures between 550º - 790º (1025ºF - 1450ºF).
      I'm looking for a good power supply of 48 V -. 20 Amp, according to your information.
      Pls let me know your opinion.
      Thank you
      Joao Ferreira

    • Artistic Diyer
      Artistic Diyer 3 years ago

      yes does work good, but you do need a good power supply capable of putting out at least 20a continuously.
      or use two or four lead acid battery's in series. not got a video of it working.

    • Joao Ferreira
      Joao Ferreira 3 years ago

      Can you inform about your 1000W Heater, model, price etç? Have you a video of working?

    • Artistic Diyer
      Artistic Diyer 3 years ago

      +Artistic Diyer got it from this website here

  • Alex V
    Alex V 3 years ago

    So keeping the frequency at the resonant frequency maintains the temperature and raising the frequency above the resonant frequency raises the temperature? Wouldn't the peak temp. be at the resonant frequency?