I am building a CNC-like machine using a microcontroller and 'FMD2740A Microstep Driver' modules to drive the stepper motors.
My problem is the vertical axis where, despite a counterweight, there is a load to lift. I want the driver to keep current flowing even after I've stopped sending it pulses. This particular power driver module (MFD2740A) turns off the power a fraction of a second after the last pulses were given. The motor can then free-wheel from the weight of the machine.
I imagine that this is a common problem. My question is two-fold, 1-has anyone used a stepper motor driver in a way to keep the power on, and 2-is the heating issue of having current on constantly a problem?
For the controller I'm using GRBL on an Arduino, an 36V motors.
(later edit) turns out the Gecko GM215 has a dip switch which turns off this behaviour. Looks like I need to just buy this module and not use my MFD2740A. See my answer below.
(another edit) the GM215 does indeed fix this problem, with the DIP switch setting for the standby mode set to OFF, it keeps the current flowing. And after keeping it on for 20 minutes I don't feel any appreciable heating, so that addresses my overheating concern.
Best Answer
If your stepper motor driver does this, and there is no way to override it, you have a crappy stepper motor driver.
Most sane stepper drivers have that sort of behaviour as an option, if they have it at all.
Looking at what documentation I could find for that driver, it claims "In static, current automatically in half", so it's not disabling the motors, merely reducing the power when the axes are static.
Considering it's a Chinese no-name product, I think the only reasonable options are:
We can possibly help with 2, but you would need to be prepared to damage a driver or two, and possibly not succeed.