Steppers, Power Supply, and Current

[kiltjim]

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.)

[pminmo]

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.

[kiltjim]

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?

[pminmo]

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.