Is there a way to tell how much current a stepper motor will draw? I'm trying not to overload the max current of my power source.
In this particular case, it's a 12V stepper. IIRC, the resistance is 60 ohms between 2 wires, 30 ohms between a wire and the common wire. It's a 5-wire stepper.
Is it as simple as 12V/30ohms = 0.4A? I assume it'll draw the most current starting from a start, and less once it starts spinning.
The data sheet for the stepper motor will tell you the current requirements. It's better to go larger than you think you need, in terms of a power supply. A power supply running at it's upper limit will run hotter than one running at 50 % of it's rated capacity.
Is it as simple as 12V/30ohms = 0.4A?
I assume it'll draw the most current starting from a start
It draws the most current when it is stopped. The coils are powered but not being pulsed. The maximum torque is then produced. As it speeds up there is at first no difference in the current. But when it is stepped faster the average current drops because it takes time for the current to build up in the coil. The torque also drops.
You reach a point when the torque drops so low that it won't even turn its own mass. This is the stall speed.