I am desinning a water system for my garden which will consist in an Arduino opening and closing water valves. I am trying to accomplish this within the smallest enclosure possible and I was hoping to not require any heatsinks. Somehow although the (overkill) MOSFET I am using is rated 100A at 55V but it is getting really hot when the valve is open. I measured the coil to be 25 ohms so at 12V I figure it consumes in the area of 480 ma. I am clueless as to why the MOSFET is getting hot with so little.
This is the circuit I am working with, obviously the switch will be replaced by an Arduino pin and provide 5V to the gate.
Am I missing something?