Power supplies required to drive a bunch of steppers

[danthoskin]

Hi,
It's been a long time since I got to play with the Phidgets stuff, but it's nice to be back!
I was hoping that someone could verify my thinking for me. I have a project that has a total of 18 of the 57STH56 steppers driven by 18 4a Stepper Phidgets (VINT, STC1003_0). The steppers are rated as 2.8a at 12v. Without getting into how I got there, am I correct in figuring that 2 supplies at 24v, 15a output will be enough to support those in the unlikely event that every stepper has to move at once?
Thanks,
Dan

[fraser]

That should give you (as im sure you calculated) about 1.6A per motor in a worst case scenario. The requirement depends on the load, the motor current is basically proportional to the load it's driving, and it won't draw more than it needs to move steps. If you're not expecting a ton of load on the motors, it is likely good. If you have large amounts of torque acting against the motors at all times, you may run into issues.

Current is generally in a worst case scenario when they are holding position, rather than moving.

[fitchett]

It's actually more complicated. Holding current is usually the worst case current, but not the worst case power.

I bet you will find that a single 24V 15A power supply will happily run all your steppers. If you think there is a possibility your application will call for all steppers to accelerate hard at the same time, you'd better separate the STC1003 into two banks, powered by two power supplies.

Don't bother getting the PSU4017 power supply - it's current limiting functionality is not useful for stepper motors. The less expensive PSU4016 will do just fine.

[danthoskin]

Thanks guys. Your help is much appreciated.
Dan