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Autotuning Induction Heater Update-Fun with Steel Bolts

That’s induction and heater is simple to construct and uses the same technology used in single resonant Solid State Tesla Coils (SSTC). Inductive heating with this unit have been optimized and I go through some of the changes that made it work better. Also, for a link on how to make this particular unit check over here: https://autotuningmainsinductionheate... From what I have learned so far, the main thing that helped to improve performance was a better impedance match between the coupling transformer and the series primary tank circuit. This made a huge difference in heating effect as demonstrated in this video. How this works: The coil shown here uses a small 100 turn current transformer and burden power resistor of about 20 ohms such that 1000A=200V. 200V is too high so I use a current shunt which is 1/10 the cross sectional area of the 3/8” copper tubing to give a more manageable 20V. This is clipped by a series of zeners and clipped down to a 5V square wave which is fed jnto a hex inverter which runs the feedback loop. I’m using a water block to cool the FETs and the work coil. When the input voltage is low, there is not enough current in the primary tank to initiate current feedback. The low signal generated by the 555 is attenuated by a 7.5kOhm resistor and appears on the input pin of the hex inverted as a clipped off sine wave which shows up on the input pins of the inverting and non inverting mosfet driver chips as a rectangle wave (less then 50% duty cycle). The narrow rectangle wave provides some heating but not much. It is a good way to control the power use by the system. When voltage is turned up the current in the tank increases a lot and then feedback loop kicks in as the feedback signal is only attenuated by a 150 Ohm resistor and overrides the low signal from the 555 which is attenuated by a 7.5 kOhm resistor. At this point the duty cycle jumps to 50% now with square wave input to the mosfet driver chips. Heating and current draw markedly increases. When the work coil is not loaded, the current draw increases to 30A or greater which is hard on the mosfets and tank capacitors. If I could come up with a circuit perhaps using a relay switch controlled by a microprocessor to turn off the feedback signal from the current transformer when the coil is not loaded, I would have a product that is bullet proof. So far with this build I have not lost any MOSFETs. If anyone has any suggestions such as using an ATtiny 85 or similar microprocessor to control a relay switch to turn off feedback at say 30A DC current draw, that would be awesome!