I am having an issue with my circuit. Specifically, with the FQP30N06L MOSFETs failing after only a couple of runs (a run being powering the circuit).
I'm using a 24V DC power supply and originally had a 3V Arduino running the program, but I switched it to a 5V in the hopes that this would solve the issue (it did not). Each MOSFET is connected to a KVLA105-5P 1" x 4" heater element, that's supposed to turn off once it reaches a set temperature.
What tends to happen is either it won't stop or it won't heat up at all (I've had both happen a number of times, right now it's not heating up). I checked the pins on the Arduino and they're behaving normally (high when heating, low otherwise). If it's heating but not stopping, the voltage across the heater is around 24V and if it's not heating at all, the voltage is zero. It does not get hot in either scenario.
I've replaced the MOSFETs a dozen times at this point and it always solves the problem, but I don't understand why they keep failing. Why do they keep failing?
I've updated the schematic as well as added images of the board. In the original schematic I had the gate grounded and the source hooked up to the Arduino. This configuration did not work as in there was no measurable difference between having the transistor or removing it entirely. Troubleshooting-wise I've replaced the 3.3V Arduino with a 5V one and added a level shifter (the screen runs on 3.3V logic), I've tried switching the power supply (have used both a wall connection via power jack and a standard external DC power supply) from 12V to 24V. I have tried adding each component one at a time and everything worked until I moved it to the system (I was testing using a different set of heaters but even when I move it back to those it no longer works) Right now, it is not heating at all and both of the leads to the heater are measuring 24V.