 How to mod a commercial induction stovetop for power control
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Dago
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Tue Feb 22 2011, 07:32PM
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Registered Member #538
Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181
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I'm going to make a sous-vide cooker (basically a 50-65C or so immersion heater that is temperature controlled) and I was able to buy an induction cooker cheaper than a regular tabletop cooker. I pulled it apart and drew schematics of it:
Power/power supply side: 
Controller side:
Then theres the board with three 7-segment displays and a few leds and buttons and a 74HC164 for control but I didn't bother drawing it. It is connected to the "Buttons" connector next to the controller.
So basically it is controlled by some mystery controller (probably some proprietary IC) since I was not able to find any info on it (heres a picture of it with markings: ) that has sense wires going to a current shunt (just a thick jumper on the board), and to the both connectors going to the heater coil (IGBT drain and after the impedance matching coil). Theres also some sort of temperature sensor (or possibly a hall sensor with a magnet but I doubt it) in the middle of the heating coil connected to the HITE connector. Also a thermistor on the IGBT and some sort of connection going to near the SMPS (AC_TF connector) which I'm not 100% sure what for (possibly phase locking?).
So basically I need to modify it so I can adjust the power with a separate microcontroller to make it temperature regulated. What I'm currently thinking is to adjust the cooker for full power and then somehow "cut" the control signal (via PWM) going to the IGBT which should be pretty trivial IF the onboard controller won't freak out. Other method to adjust the power would be to adjust the feedback lines somehow but that would make isolating the external controller a tad harder. Using the pre-existing power settings won't work because even the 1st power level is too high (and theres ten of them), water will heat to over 50C.
I haven't done any scoping yet because I don't have a suitable isolation transformer, but I'll try to borrow one somewhere.
There are a couple of extra pictures here:
Does anyone else have any experience hacking these induction cookers or have any idea on the onboard controller type and how it might react if I fiddle around with the drive signal going to the IGBT? Or any other idea on how to adjust the power?
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