In theory, yes. Probably more than double. Sorry, this won’t be perfectly clear, and it probably isn’t perfectly accurate.
The steppers produce current when they move. You might have seen the machine come to life when you move the gantry quickly with the machine unplugged. They do this when powered too. That current goes against the power supply and can be thought of as a voltage.
If you have a 12V power supply, and there is some loss due to wiring and connectors and driver stuff, maybe 9V is reaching the coil.
If the motor is stationary, it isn’t creating any of that backward voltage, so 9V is causing a big current in the motor. Maybe 2A. The driver is measuring the current going to the motor, and it is set to 0.9A (or something). So it turns the voltage on and off quickly (by adjusting the duty cycle of the PWM) and it means that the 9V is maybe only going to the motors 40% of the time.
If the motor is moving (this is dependent on the rpms of the motor shaft, not anything that is attached to it), then it might be fighting that voltage with 6V. At that point, the effective voltage going to the coil from the power supply is only 9V-6V=3V. That would (in our imaginary motor) make the current (when on) 2A/3, or 0.6A. The driver then leaves the power on constantly, but it can’t make any more power, so the motor acts like the driver current setting is 0.6A. That results in a lot less torque, and the motor can skip steps. The voltage generated by the motors is doubled when wired in series vs. separate drivers.
If you had a 24V PSU, then you might get 21V at the coil when stationary, and 15V when moving at that same speed. So instead of the driver getting effectively 3V to run the motor, it has 15V.
That is pretty convincing, I know, but I should also point out that if the driver is working at a lower speed, and the voltage generated by the motor is smaller, then the driver can still reach the 0.9A set point, and there is absolutely no difference between the power supplies.
This is the mental model I have in my head. It leads me to these conclusions:
- A higher voltage power supply does not lead to more power at low speeds. We need the most power when milling (not traveling). A 24V PSU is not useful for most CNC machines.
- A lower voltage power supply will reduce torque at higher speeds.
- A higher voltage power supply is about raising the ceiling on speeds where you can still have strong torque.
You can calculate the point where the drivers are in saturation. You need to find the number in the stepper motor spec sheet that shows how much voltage it generates per rpm. You need to calculate the voltage drop up to the point of the motors (or make a good guess). You need to determine the voltage needed to reach the set point current given the resistance of the motor. So if the motor is 5Ohms per coil, and your set point is 0.9A, then you will saturate at 0.9A*5Ohms=4.5V. So if your power supply is providing 9V to the coils, then you need 4.5V to drive the motors at full current, then you can have up to 4.5V feedback from the motors before you saturate. That will give you a max speed at the motor shaft, which you’ll have to convert to mm using the geometry of the machine.
It is also possible to drive the machine past the saturation point. You’ll get most of the torque you asked for. So if you’re skipping steps at 480mm/s, you might reach saturation at 360mm/s. I don’t really know.