I'm building a thermostat for a TEC-based minifridge I built last summer.
Using the 555IC and a thermistor, I plan to create a 30Minutes defrost cycle when the temp falls below 3℃.
The defrost cycle is implemented by switching the peltier (modeled as a 120W bulb) power from 12V to 5V*
The whole device is powered by an old ATX PSU rated for 300W, so I get 3.3V, 5V and a 12V rails for free.
*from what've I learned switching the peltier completely off will induce thermal stress on the TEC couples leading to shorter life for the device.
The 555 is powers a 6V relay that switchs off the 120W load.
The 555's trigger is connected to a voltage devider where the lower potentiometer+resistor simulates the thermistor and the upper potentiometer enables temp control.
I set the 555 cycle to ~5 seconds in the simulation to make it presentable
