Optimal Motor Voltage

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16 Feb 2022 16:56 #235050 by Kylehopestolearn
I am looking to understand optimal voltage for my motors.  From what I understand voltage is dictated by motors and then multiplied by driver specifications. I have 57HS76-2804-05 motors with ST-4045 drivers.  The spec sheet on the motor is 3V 2.8A.  I can't find any optimal multiplication on the drivers specs for motor voltage.  I run one power supply at 25volts (specs say output can be up to 20amps).  My drivers are set to 3amps with switches. When all three axis are moving I get errors or 2 axis many small movements and wondering if my voltage is wrong.  I understand the 1.89N.M of the motors is not large and the z weight might be pushing the motors capability but want to understand voltage and amp draw before I make that conclusion.  Each axis moving individually works fine and precise.  Multiple axis over time get missed steps and the z can drop in height during movements so before I get better motors I want to understand my errors.   Yes I need to do the math on weight of my gantry and z axis and calculate needed motor strength which I am currently trying to do but understanding optimal voltage is something I need to understand also.  
Any advice or input would be great. 

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16 Feb 2022 21:00 #235078 by tommylight
Replied by tommylight on topic Optimal Motor Voltage
There is a lot of very bad info on the net regarding stepper drives and motors (and everything else), so i am not in the mood of starting a fire right now, so here is the very short version:
-Voltage does not matter, current does
-Some math that voltage has to be a multiple of something or another is wrong
-Use the voltage the drives can safely handle, cheap drives if it says 50V = use 36V max, good drives use whatever is close to max rated
-If you need speed from stepper motors, it is imperative to use low inductance motors, 1-3mH max
-Mind the current settings on the drive, on cheap drives you can go 20% above motor rated current, on good ones 20% below. Also mind the peak and RMS values, ignore peak at all times.
-I have 2.3V stepper motors wired to Lam Technologies drives running at 75V for over a year, still no smoke! :)

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16 Feb 2022 21:47 #235083 by Kylehopestolearn
Thank you again.  Everything you said does align with what I've been able to read on the web including that there is a lot of bad info.  Also the more I learn it is very apparent that you get what you pay for when buying parts.  
The following user(s) said Thank You: tommylight

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17 Feb 2022 09:55 #235111 by tommylight
Replied by tommylight on topic Optimal Motor Voltage
Do not overthink it, just get something usable and make it work, later it will be much easier to choose what you need.
Also you did not say what errors you get.

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17 Feb 2022 11:52 #235124 by Kylehopestolearn
As for the errors I get.  Since I've built the machine from scratch I have encountered a lot of errors but I'm down to just one that stops me from using the machine for what I want to do right now.  I want to do some wooodworking to start with.  I ran my first 3.5 hour program (a 3d roughing pass) so single z movements and x y clearing.  It did that correctly for the first time (I was happy).  I tried a 3d finishing pass so many movements all axis.  The z axis either took extra steps down or lost up steps.
This error makes me think it is either to heavy for the motor although test axis up and down for 10min works no issues or I am losing power to the motor.  I wanted to try to understand the total lack of specific power supplies out there for motors better.  I am going to first try to increase voltage to say 36 and run the 3d finishing pass.   It messes up not long into it if it's going to mess up. 
My trial and error method is going to be: increase voltage, increase driver amp setting, run two power supplies

I am happy I have had all the problems I've had so I could learn what I have about self built machines.  This forum has helped me understand so much above Linuxcnc so many thanks again.   

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