I get where you’re coming from with the wattage calculation but you can’t apply it in that way to this situation from what I can see.
The drivers we’re using are chopping the input voltage at high frequency to try and maintain the current that we want. This means that the motor won’t receive your power supply voltage directly, so a wattage calculation using P=V*I with the supply voltage as V will give you the incorrect value.
The torque is proportional to coil current so you’ll lose a lot of torque if you use that method when setting up your stepper drivers. I’ll verify it once I get my DRV8825s but they’ll be a few weeks.
Saying that, we won’t be able to run the motors at full current anyway because they’ll be too hot for the PLA mounts. We should adjust them to get the best balance we can between motor temp/driver current+temp/torque though.
My motors are specified for upto an 80c rise above ambient so I know if I ran full current the PLA would soften.
Btw, absolutely love your design. I can’t wait to get it up and running, I’m printing off all the parts while I wait for some of the stuff to arrive from China.