@John P, what I meant is, the heat rise in the mosfet is due to the Rds times voltage in. With Rds meaning resistance - drain to source.

This has nothing to due with the amount of Watts that a mosfet can transfer, when fully turned on. The fully turned on state is limited to the TO-220 package, which is set at ~75 Watts by the JEDEC.

 

Highly theoretical, even 50 Watts are not possible even if you have a good cooler.

I have run some experiments with these IRF MOSFETs. You can approach about 40W but that's it- coolers get very hot and that's no good for surrounding components. TO218 transistors are more appreciate for larger currents.

You should have some reserve or the component will explode if you have a small current surge.