Induction Range

Custom Search

since 08/13/09

The induction range is a nifty kitchen appliance. It heats the cooking utensil by inducing high current to flow in the bottom of the pot. This high current causes ordinary ohmic heating. The major advantage of the induction range is efficiency. The range itself does not get hot. Indeed, one can lift the pot from the range and then (carefully) touch the top. It can be quite warm from heat conducted back from the pot but it will not be red hot, as with a conventional range. Very little waste heat is released to the room. I especially appreciate this characteristic in my motorhome which has limited air conditinoing capacity to begin with.

In this section, I present a short dissection of an induction range that was sold by the QVC network for a time. I bought several non-working returns for a song. The easily fixed problem is visible below.

Here is the range as it arrived from the salvage company. Nice and compact. The top is heat resistant ceramic to resist the heat from the cooking utensil which can be quite high in the case of a fry skillet.

The innards. The round orange coil in the center is the induction coil that projects a magnetic field up through the ceramic top and into the utensil. The circuit board and power stages are below the coil. Pay attention to the upright toroidial (orangish) coil at the lower left of the PCB.

This photo shows the control board with the inductor lifted out of the way. The little square metal can in approximately the center contains the microprocessor that makes the unit run. It is shielded from the intense magnetic field for obvious reasons. The power FETs are attached to opposite sides of the heat sink. This unit uses essentially the same half-H-Bridge architecture as I did except that the work coil is not resonated. This works well when there is room for a number of turns on the work coil and where a ferrite magnet concentrator can be used.

Here is the work coil. It is a helical coil wound with Litz wire. The black plastic looking stuff is the ferrite magnetic field focusing core. It's solid under the coil so that the field projects upward. The white thing in the center is a thermostat that rests in contact with the ceramic top. It shuts down the unit if the top overheats.

The guts splayed out. The bottom of the board uses a clever array of solder bumps to increase the current carrying capacity of the copper foil. The black thing at center left is another thermostat to protect the electronics from overheating.

Why the units were non-functional. This is the back side of the board where those torodial coils rest. The coils were supposed to be secured to the PCB with squirts of glue but the machine apparently misfired. The heavy inductors were left to flop in the air and shipping jolts broke the solder pads. Trivially easy to fix.

Another view of the broken PCB pads. This is something to look for in any electronic device that contains a switching power supply or switching electronics. This is the first thing that I look for when I receive a non-functioning piece of electronic gear.