How to calculate Power supply minimum current limit

[[Beer]]

Hello!

I am a bit confused about minimum current limit of power supply unit (PSU).

For example.
Let's say I have a 2 phase stepper motor with 3A / phase.
If I understand this right, then 2x3A = 6A per motor.
Since I am building 3 axis machine (3 motors), then...
3 x 6A = 18A (on full load I guess. So this would be maximum)

Usually Voltage range is specified for the controller (e.g. 20-50V), but no current limit.
What is MAX power of the motors: P = U*I = 50V * 18A = 900W
What is MIN power of the motors: P = U*I = 20V * 18A = 360W

Ok. So it depends on motors power supply!

But....
I found a controller with MAX 20-36V max 3A/phase (motor: 3A/phase)
PSU DC output: 30V/5A
So according to my previous calculations: 3 motors sink max 18A, but PSU can source max 5A.

What is the trick?
Is it all about pulses? PWM?

How do I calculate minimum current limit for my PSU?

I appreciate all answers

[Beer]

[H.O]

Hi,
Have a look at the Step motor white paper published by Geckodrive. Some of it may be specific to Geckodrive products but it covers a lot of general step-motor theory.

[[Beer]]

Great document.
Thanks for sharing it.