Friday, 1 January 2016

Understanding how much power a stepper motor draws


I had a previous question describing a power management system where I was trying to power 7 stepper motors from a wall outlet (with switching power supplies and motor drivers). I realized during this question that I may not understand how to fully calculate how much power, in Watts, a stepper motor will draw.


Setup:


enter image description here


Questions:


1) What is the maximum power that this motor can draw in the described setup? How do the calculations from phase current + suppler voltage + motor parameters (see below) relate to the torque-speed calculations for finding power? E.g. it'd be nice to see something like P = V * I = Torque * Speed so in the future I can estimate missing quantities quickly.



2) Can I limit the power drawn by the motor via the motor driver, by choosing a lower current mode?


3) How does microstepping affect power usage? By default I will probably microstep to 400 steps/rev (by half).


4) Are there any random events (like stalling, first time starting up, etc) that may cause large unexpected spikes in power consumption? And can I count on the PSU + motor driver to protect against it? They claim all sorts of protection features.


References:


Example Motor Specs:


Phase:  3
Step Angle: 1.2°
Holding Torque: 2.0 Nm (283 Oz-in)
Phase Current: 5.8 A
Inductance: 1.85 mH

Resistance: 0.62 Ohm
Rotor Inertia: 0.00818 oz-in-sec2

http://www.americanmotiontech.com/products/productdetail.aspx?model=es-m32320-283-oz-in-3-phase-nema-23-stepper-motor-1000-line-encoder


http://www.omc-stepperonline.com/24-phase-nema-23-stepper-motor-driver-2450vdc-15a45a-256-microstep-m542t-p-293.html




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