How Strict is the Max Vsupply Calculation for Steppers?

[mattnedgus]

4 years into running a DIY CNC Router and I'm still a noob!

So Part 1 to this is that:

I've been running my motors:

I = 4.2A
L = 3.2mH
V = 2.73V

on a 68V supply. The Max Vsupply = 32*(sqrt(L)) equation gives 57V. Geckos guide advises an upper safe voltage of between 4 and 20 times motor voltage, giving 55V.

My question is: Am I risking the motors running on 68V?

The reason I ask (as well as not wanting to burn my current motors!) is that I'm trying to compare the performance of three quite different motors and the calculated max corner speed varies directly with Vsupply. I was using this speed as an indicator of potential motor speed.


Part 2 to this is that:

I've just discovered I've been running my stepper drives under-powered at 3.1A RMS instead of as near to 4.2A RMS as possible (comment from Leadshine confirmed)

I think this explains why I haven't been able to rapid at speeds I'd hoped (and that had initially pushed me to consider NEMA 34's in another post) but it also means the motors haven't been getting as warm as they should. I've measured temperatures in the high 50's (degC) but I'm concerned that if I increase the current I'll be causing the motors to overheat with such a high voltage.