Steppers, Power Supply, and Current

I am getting ready to get some stepper motors, and am having difficulty choosing what I thought I needed. I am building something similar to the JGRO design. So, from what I read, I will need something in the area of 275+ oz-in motors.

I have a power supply from some old equipment, Regulated 24v @ 4.5A. I am not sure if this is going to be enough. I will be using a A3977 board to drive the motors. With this, the whole system should be limited to 2.5A * 3 = 7.5A, way too much. But I do understand that I should rarely get anywhere near that.

I have read the write-up from Gecko, and saw (sorta of understood) that a motor should pull no more than 2/3 of its rating. What I see available from all the places I've found is that a 275-oz-in-ish motor should be close to 2A a piece.

I am completely off base, or am I going to be close enough to get started?

(I do have plans to upgrade the power supply, but not right away.)

The question is what do you want to accomplish, and how fast. Speed costs, patience costs less. People have a tendency to look at all three axis the same and they are not. A moving gantry design like a JGRO needs on the X axis are different than it needs on the Y or Z. In all honesty, the a3977 on a JGRO X wouldn't be my recommendation. A high 200ozin stepper is enough power but if you want X rapids to be snappy you need a higher voltage driver on the X. The A3977 is perfect for the Z, OK on a Y as long as the correct motor is used. Works on the X, but it is methodical.

Thank you pminmo. I truly appreciate the input.

All of that had occurred to me, in some form or another. However, the X-axis on my machine will be driven by a set of acme threads, and the y-axis will be the standard all-thread (unless I can help it). So I was kind of figuring that I would have pretty good X motion, and slower Y. But since the machine would have an extended X, I was hoping for a pretty good trade off.

My question was more towards how much current would be required under realistic circumstances, and if my power supply would meet the need.

Any thoughts?

You maybe a little light on the power supply, but if you already have it, I'd say use it and monitor it. I've done 3 axis of 3977's with two 2A phase motors and a 1A phase motor with a 4A unregulated supply with no issue. But it was an unregulated supply at 29V with a substantial filter cap.