So I bought a stepper motor, but I need to know how much current it will draw so I can get the appropriate power source. The motor is described thusly: Portescap #S42L048S02-M5. 24V, 5 Ohm, 7.5 Degree per step. 42mm diameter x 22mm. Two mounting holes on 51mm centers. Four 3" leads. Shaft - 3mm diameter x 11mm long. 16 tooth, 9.75mm diameter brass gear.
Notice it doesn't say anything about amps. But I thought about Ohm's Law (V = I R) or (I = V / R). Does this mean that at 24 volts it will draw 24 / 5 = 4.8 amps? That sounds a little high to me.
Your calculations sound right; this is a relatively beefy motor. Worse, it's likely 4.8A per phase, and there are two phases so you will be drawing 9.6A from the power supply worst-case.
Of course, you don't have to run the motor at its full rated current. You can either apply less than 24V or use a current-chopping driver that allows you to explicitly set how much current you want, regardless of applied voltage.
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Reading around I do see that some manufacturers -expect- current control to be used on their motors. From there I had a bf and went to Portescap and found that they don't list that motor but do have a 42L048 family. I looked through -all- the can-stack steppers at Portescap and -none- of them are over 12V. Further, only the 5V motors have such low resistance.