I want to operate a 12V automotive fan with a 3.3V uC signal. The (37-year-old) centrifugal fan draws 3.2A for about 100ms at startup and then a steady 1.2A while running for a maximum of 30 minutes. Originally, I used a Panasonic 12V, 25A automotive relay (www.farnell.com/datasheets/1809465.pdf) and 2N2222 NPN BJT. I also added a 100Ω resistor and 100nF cap across the contacts. The circuit works fine on the PCB I prototyped.
I assembled a second circuit and replaced the relay with a 27A P-channel power MOSFET (www.farnell.com/datasheets/1712479.pdf). Assuming I understand the data sheet correctly, there is already a diode present so that component was deleted as was the RC snubber. I can also operate the fan now at various speeds using PWM. This circuit also works fine on the breadboard.
There are similar threads but I haven’t noticed a consensus on whether a power MOSFET is considered a suitable replacement for a relay. I don’t need the PWM option and am unsure if it is even advisable to operate the fan at anything other than its designed parameters. The MOSFET is $1.50 but the relay is only $3.50, not a consideration for a one-off. Should I prefer one design over the other? Should I use a FET rather than the 2222 BJT if I want to use PWM? Is the RC snubber necessary for the relay? Is there anything else I haven’t considered like excessive heat when using the MOSFET?