I am currently designing a circuit that includes a nichrome coil used as a heating element. The wall adapter is 25V 5A DC, which leads to different buck converters that takes it down to the appropriate voltages. The Buck converter that leads to the coil is set to have an output of 15A. The Flow to each component including the heating coil is controlled by a number of MOSFETS.
I have noticed that upon testing the heating coil (in testing I have separated the component being tested from the others so in this situation the power goes straight from adapter to buck to coil to MOSFET then back to buck), the MOSFET (which is rated at 30A and 60V) is overheating and melting. I have tried using heat sinks, splitting up the current between multiple MOSFETS, and added PWM to allow the MOSFETS time to cool down, but I can only make the PWM rest periods so long before I can no longer achieve the desired heat. Still with all of this, the MOSFETS heat up and begin smouldering.
Because of the amount of MOSFETS I've ruined and amount of dangerous fumes I've inhaled, I feel it is time to turn to the experts for insight.
My assumption is the circuit is in essence a short circuit, although I would have assumed the coil would have supplied ample impedance.
Does the fact that the buck converter is lowering the voltage mean that excess amperes are being drawn?
On a side but still related note, if the circuit is in essence acting like a short and drawing uncontrolled current, will this risk damaging the adapter?