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Last update 02/17/2009

Induction Range

 
Ranges inducted since 05/27/07
An induction range heats the steel pot not by applying thermal heat but by inducing a heavy high frequency current into the pot's bottom.  Inside the range is a multi-turn coil that serves as the primary of a transformer.  The pot's bottom serves as the one turn shorted secondary.  Thousands of amps flow, very rapidly heating the pot and cooking the food.

A thought immediately comes to mind - can an induction range be used or converted to a neon electrode induction heater?  The answer is provisionally, yes.  The range has the ability to tune itself to accommodate different size pots and pans.  And it tries to protect itself from running unloaded by detecting the presence of the pot of appropriate metal (iron or steel, aluminum is too conductive) and turns itself off if there is no load (pot).  Making the range work as an induction heater will revolve around controlling the power and fooling the protection and tuning circuits or bypassing it.

My first experiment (sorry, no pictures) involved winding a coil similar to the primary one and placing it on top of the range.  Heavy leads carry the current to the work coil of a few turns that loop around the neon electrode.  This showed great promise, though the protection circuit was touchy.  I played around with adding pieces of iron plate on top of the coil.  That helped but the real solution will be to defeat the protection circuit.

Meanwhile, enjoy some pictures of the internals of this one.  This model was sold on QVC.  This one and several of the others are warranty returns.  All had the same problem - an inductor missed getting glued to the board and shipping vibration broke the solder joints. Their carelessness = my gain!  I bought 'em in a box of misc junk at a flea market.

As I recall, this unit runs at about 35khz, a perfect frequency for neon induction heating.  New, this consumer model is less than $100.  I see them occasionally in pawn shops and at flea markets.  Something to keep an eye open for.
 

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The unit with the ceramic lid removed.  The orange spiral is the induction coil, would with Litz wire.  The greyish-black frame around the coil is a ferrite core/support.  
With the primary coil removed.  The heat sink contains one big honking power MOS-FET that drives the coil in a half-bridge configuration, the two gum drop caps below the heat sink forming the other half of the bridge.

The power electronics are directly line-operated.  The two toroids at the lower left are EMI filters and are what vibrated loose during shipping

 

  
A closeup of the primary coil.  The Litz wire construction is plainly visible.  The thing in the center with the white goo is a thermal sensor that turns the unit off if the ceramic plate gets too hot.  
The bottom of the main PCB.  The numerous little solder blisters on the traces is a trick to increase the current carrying capacity of the trace without having to go to thicker copper foil.  The black thing in the center-left is a Klixon thermostat to protect the power semiconductor.  
Why I got these things so cheap.  Here is where the toroid's weight broke the solder pad during some impact.  There was a spot of hot glue on the toroid but apparently the ChiCom slave laborer in charge of glue squirting missed.