How Strict is the Max Vsupply Calculation for Steppers?

[Neale]

One possible reason for different temperatures for the two motors on your Y axis is whether or not you have "half current when stationary" selected on both. A lot of stepper drivers have this option available - it cuts motor current to half normal value if the motor is just holding position and not moving. I'm only guessing here - I would expect the DIP switches on both Y drivers to be set identically.

[mattnedgus]

...the corresponding external case temp of the motor would likely be over 100C...

Hi Muzzer, thanks for your explanation! Sorry I'd not seen your response when I just made my last reply.

It sounds like I was maybe OK with a 90+degC case temperature for a short time then (but it didn't half heat the garage up!).

Would I be right in thinking that:

When using higher voltages (within driver spec), the only real reason to set the motor drivers Peak current to match the motors rated current is to keep the temperature down? Higher voltages are preferred to achieve higher-speeds when direct driving because current flows in and out faster, letting the coil get to a higher current/field strength/torque per step.

- e.g. I supply 68V and I set motors (rated at 4.2A RMS) to 4.3A Peak in the driver (equivalent to 3.1A RMS in the driver on the Leadshine DM856)

And so conversely:

If I wanted to set the motor drivers RMS current to match the motors rated current, I'd need to keep the voltage down below those values generated by Mariss Friemans max Voltage equation to manage the temperature? Greater current flowing in the coil would produce greater torque, but having to run at a lower voltage would mean lower top-speeds.

- e.g. I supply 50V and I set motors (rated at 4.2A RMS) to 4.0A RMS in the driver (equivalent to 5.6A Peak in the driver on the Leadshine DM856)

I've seen so many good but contradicting views on whether to use the Peak or RMS values but I don't understand the fundamental reasoning behind them and this is the best I can figure out at the moment.