MPCNC: 12V or 24V?

wilriker

I am thinking about (or rather try to not think about ) building a MPCNC. Since it does not have any heater components (with high currents) and probably won't move very fast (at least not while cutting) I think 12V would be sufficient assuming the spindle will be powered separately.

Is there anything I am missing that would be improved by using 24V?

Veti

you want 24v for the nema motors.
You will get more torque out of them.

wilriker

@veti Why would 24V result in more torque when the motor drivers are current based?

dragonn

@wilriker At high speeds. Read about BackEMF.
When the motor BackEMF exceeded the power supply voltage stepper motors are losing torque.
And a stepper driver can not push more then the power supply voltage.
That is why stepper motors in CNC a driven often with 40-50V

wilriker

@dragonn I know about the high speed part. But for a MPCNC high speeds are only for travel and I could live having them at say 100mm/s max. I don't think I will be cutting with 100mm/s. Except maybe paper.

dragonn

100mm/s doesn't really tell much because what matters is the rotating speed of the motor.
https://reprapfirmware.org/ here is a nice EMF calculator, just do you math for 12V and 24V

deckingman

@wilriker
Manuel,

Turn your question on it's head. Then it becomes "why would a 12v PSU be better than a 24V one"? Generally, they seem to cost the same. The answer may be a factor of what other peripherals do you want to power ( fans, lights etc) and are these peripherals available one voltage but not another?

wilriker

@dragonn I know the EMF calculator. It was probably the most visited webpage in my browser's history for quite a while while I was selecting new motors for my printer.

@deckingman I think your idea is the better approach here. Also currently this is all in the just-wanna-have-it stage. I have absolutely no need for a MPCNC I would just build it to have it built.

And you are right, peripherals are (in my experience) more widely available for 12V than for 24V.

I am going to mark this question as solved with: 24V is always better for your steppers because they could run faster than with 12V. And a buck-down converter can always take 24V to 12V in case of peripherals not available at native 24V.