A Simple Induction Heater

For those of you not familiar, an induction heater is a device capable of heating something up very rapidly using a changing magnetic field. [RMC Cybernetics] decided to build one and was nice enough to write up the project for the Internet’s learning and amusement. A full explanation as well as a schematic and build instructions are provided on their website.

This heater works using a principle involved in most transformers. When there is a change in the magnetic field near a conductive object, a current will be induced in it and it will generate heat. Interestingly enough, while transformers are designed to minimize this heat, an induction heater instead aims to maximize this heat in whatever object is placed within the coils.

[RMC] Has provided a video of how to build the heater as well as it in action after the break! Skip to to 1:42 to see the heating in action. Or watch the whole thing to see how it’s built.

[youtube http://www.youtube.com/watch?v=2-EZ3M31Zj8&w=470&h=315%5D

23 thoughts on “A Simple Induction Heater

  1. That’s quite clever, I wonder if it could be used as a soldering iron? You’d have a “ink pot” containing the coil and a simple metal rod with a handle, a bit like his screwdriver. You could have many metal rod with different head size.

  2. every time i see an induction heater, i’m wondering, what would happen if something (metal) or someone accidentally touches the coil. they are always avoiding it, so i guess something bad ?

    1. Ferromagnetic metal would obviously become hot. But others like aluminium wouldn’t. People would be a problem if the coil is not covered, as someone could get shocked. Simply cover the coil with epoxy or any other heat-resisting, fire-proof, non conductive sealant and it’s not a problem anymore. I have a induction cooktop and I love it :)

  3. I’ve never used one but these are fantastical for old cars with rusted/seized/stuck bolts. Oxy/acet torches work just like these but may set fire to rubber bits or electrical wiring nearby.

  4. There’s no danger from putting your finger into the center of the heating coil because I^2 is kept low by the high resistance (R) of your finger. (actually, that’s the DC P formula though, but close enough for the girls I go with)

    And there’s no danger of electrocution either because of the low voltage even though the current is high.

    Just keep in mind, you’re always using electricity when it’s turned on (although not nearly as much when there’s something metallic sitting in the coil, but I don’t think I solder fast enough to use one of these without it cooling off too soon. It’d make a heck of a branding iron though! :)

    1. http://en.wikipedia.org/wiki/Aluminium
      Electrical resistivity for Aluminium at 20 °C is 28.2 nΩ·m
      Melting point is 933.47 K, 660.32 °C, 1220.58 °F
      Molar heat capacity is 24.200 J·mol−1·K−1

      Or recalculating from Molar heat capacity into grams heat capacity is 0.897 J·g−1·K−1
      Or it’s Volumetric heat capacity is 2.422 J·cm−3·K−1
      Which value used depends on whether you are using metal weight or volume in your calculations. The numbers will show what you would expect: a tiny hollow fragment will melt, and a large solid piece of metal will warm up. All you are doing is transferring energy from the primary winding into the short circuited (Aluminium to be melted) secondary winding in a transformer.

      So we need to workout the energy required to raise the temperature of some Aluminium (1g) from average room temperature of 20°C (293.15K) to Aluminium’s melting point at 660.32 °C (933.47 K). A temperature increase of 640.32 °C or 640.32 K.

      So the energy required is 0.897 J·g−1·K−1 by 640.32 K which is 574.36704 J·g−1

      So if you had 10 grams of Aluminium then you would need 5743.6704 Joules of energy to raise its temperature from room temperature to just it’s melting point. But this is a lower limit because we have ignored any radiated or conducted heat away from the metal or any stirring Eddie currents within the metal. We are assuming that as the temperature increases that these constants remain constant, which is not the case. e.g. Aluminium’s Electrical resistivity increases like most other metals as it’s temperature increases.

      Electric power
      Power is the rate at which work is done. It has units of Watts. 1 W = 1 J/s

      So if the primary coil is providing 10 Amps at 30 volts, AKA 300 Watts
      And assuming that 100% of the primary power is transferred to the secondary, which it isn’t.
      300 Joules of energy is being added to the short circuited secondary winding every second.

      So a 10 gram piece of Aluminium should melt no faster than after 5743.6704 / 300 = 19.1 seconds
      And a 100 gram piece of Aluminium should melt no faster than after 57436.704 / 300 = 191.5 seconds

      The real issue is that as the piece of Aluminium gets bigger and bigger more energy will be lost through convection, conduction, Eddie currents before the metal has a chance have enough energy transferred into it to melt.

      I am totally ignoring some of the underlying physics involved to make most the maths as easy as possible.

  5. Yikes! More physics than I understand. But it sounds like yes, it would work, depending on time and weight/volume? You could make a fancy little mass-casting machine with this. A conveyor belt with little forms, going under a melting machine…

    1. It is not that complex. The summary is: Io raise the temperature of a piece* of Aluminium metal from room to melting point takes Energy. The source (primary winding) is supplying 300W, which is 300 joules of energy added every second. Assuming that all the energy added to the metal, and all of it stays there (both of which are false assumptions, but good for a very rough initial lowest ballpark figure). The answer is how long it will take to add the energy and melt the metal in seconds.

      I added the maths just to show how to use the numbers from Wikipedia can be used. But I’m leaving out the bit about how useful skin effects are on the secondary (metal to be melted) and ideally using Litzendraht wire for the primary coil to reduce skin heating effects on the primary source coil.

      *piece – is a fixed volume or a mass of the Aluminium metal.

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