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Hopefully this is not as off topic as it might seem.

Some background information:

I've created the coil below to use as an induction heater from regular 230Vac household insulated wire. The coil is attachable to a commercial 2kWatts 230Vac induction cooktop. It works, the iron crucible lid up yellow hot. To prevent the insulation on the coil from melting I had it submerged in water, with a glass jar inside to prevent the water from reaching the crucible. But the setup is very impractical, the glass cracks due to the heat (differences?).

How can I create a coil with equal inductance and dimension that can withstand much heat and without shorting the wires (800°C or so)?

Sloppy home made copper coil inductor

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    \$\begingroup\$ You should start by using bare wire (or even copper tubing), and supporting the coils with something (ceramic? silcone?) that can handle the temperature. If you use tubing, you can run coolant through it. \$\endgroup\$
    – Dave Tweed
    Commented Feb 27, 2014 at 15:18
  • \$\begingroup\$ What frequency is being used for the induction heating? \$\endgroup\$
    – Andy aka
    Commented Feb 27, 2014 at 15:28
  • \$\begingroup\$ Isn't the goal of induction heating that the inductor itself only slightly warms up if at all? \$\endgroup\$
    – jippie
    Commented Feb 27, 2014 at 15:48
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    \$\begingroup\$ @jippie I think the issue is not necessarily the wire heating due to resistive losses, but thermal conduction from the target that is being heated. \$\endgroup\$
    – W5VO
    Commented Feb 27, 2014 at 16:15
  • \$\begingroup\$ Was the glass jar plain glass, or Pyrex? (borosilicate, like a lab beaker not the plain glass sold as "Pyrex" kitchenware in the USA?) Pyrex should stand up to thermal stress much better. \$\endgroup\$
    – user16324
    Commented Feb 27, 2014 at 17:15

1 Answer 1

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First, as Spehro points out in the comment below, you should make sure your coil matches the inductance of the original cooktop coil. This will minimize losses in the coil itself, some of which radiates as heat.

Then you should be using copper tubing for your coil, which you run coolant (often water) through. The currents going through the coil are high frequency anyway, so most of the current is in the outside of the conductor, which is fine for a tube. You'll have to make sure to properly isolate the coolant from the user, ground, and other metal and circuit parts as it will carry a small current from the coil.

There are a number of diy induction heater examples that use this technique. If you need an example, try a search for them. The image below shows more than you need. The transformer and huge capacitor in the upper left are already taken care of by your induction cooktop circuitry. The interesting part will be the copper tubing, which is connected to the plastic tubing on the lower left which then leads to a pump and a bucket or radiator.

Image of DY induction heater with coolant loop in coil

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  • \$\begingroup\$ Not sure leaving those spanners so close is a good idea! :-) \$\endgroup\$
    – user16324
    Commented Feb 27, 2014 at 17:17
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    \$\begingroup\$ Note that the capacitor is resonated with the coil inductance, so you should try to match the inductance of the original coil to minimize heating. \$\endgroup\$ Commented Feb 27, 2014 at 17:18
  • \$\begingroup\$ I've thought about a DIY induction heater from scratch. I build some 12Vdc units, but whenever I tried to upscale the voltage, the mosfets blew up. I'm not so experienced with electronics and it was costing me quiet some money, those smoking expensive high amp mosfets. Anyway, I took apart this cooktop, and calculate the inductance of the coil and made a solenoid that should approx have equal inductance. Winding that same coil with tubing, it is impossible to match the number of windings while maintaining the dimensions. But I see, I've to change my approach. \$\endgroup\$ Commented Feb 28, 2014 at 6:31

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