I would like to a build a temperature sensing variable speed fan controller for my truck. Currently using a purchased 2 speed on/off relay based controller, but my fans are overloading the whole circuit when the controller is powered on during a high speed temperature scenario. On low speed, I have the fans wired in series to spin both slower - works great. Each fan initially draws 100 amps at full 12v. On the low speed (6v/series), they cruise about 20a together. On high speed, they settle in around 25a each.
I am somewhat experienced with arduino and using a few references to build in specific features I want, but here is the main example I am going by. https://circuitdigest.com/microcontroller-projects/automatic-temperature-controlled-fan-project
My question is around the type and size of transistor that I would need to handle the amount of current these fans draw. Some examples have MOSFET while others have FET or even standard PNP. I am pretty new to working with transistors and can't find any references that make sense. Would love to get a reference to learn this calculation and appropriate type.
Edit: removed picture with incorrect wiring diagram.