Stepper driver question

Hey, does anyone know if stepper drivers (these in particular) need to be powered by the controller or can Vmot and ground come directly from a power supply?
Thanks!
joe

Which is "the" controller, or do you mean a generic controller?

The stepper driver itself can take VMOT from anywhere. When plugged into a controller board, VMOT is usually tied to heaters or other stuff. MOTGND is also usually connected to Logic GND on the controller.

But if your stepper is not plugged into a controller (or you have designed your own) then VMOT and MOTGND can be independent.

I'm using an Azteeg X3 right now running on 24V but I'd like to use 36V for the stepper drivers. Also, when all 3 axis move at the same time they seem to be bogged down. Thanks for your reply.

If you have a single power supply with multiple voltages yes. Otherwise to use different power supplies, i dont think so, and i wouldnt try it if i were you. Different power supplies can have different ground levels, and then your control logic may not be where it has to. You could tie the grounds together to ensure they are at same level, but then current may not sink balanced in grounds the same way they would if were separate. The current from both psu can get into only one ground, meaning can easily overrun one of them. To overcome that, could use two psus that are big enough, each rated higher than entire device consumption, but still personally i wouldnt try it. But its your decision to make of course.

Edited 2 time(s). Last edit at 05/31/2013 03:21AM by NoobMan.

Would it only be a problem if logic ground and motor ground are connected in the driver? Guess I'd have to find that out huh?

Be careful. First, take a multimeter and measure the voltage between the grounds. For example, you put step to 5v from one psu, and driver will have it referenced to the other psu ground.

So measure between from your controller 5v to the ground of the other psu, and see if there are 5v or not, this with grounds disconnected.

Well, how did that worked out? I'm curious.

I've actually tried something like this for the heated bed http://forums.reprap.org/msg-191972. It worked but it was a hack and it made some LEDs stay on when they're not supposed to. I've since implemented the use of solid state relays for THAT purpose. In that case the hack was using a mosfet on the ramps board to switch the ground of a 12V supply on and off. It obviously influenced the electronics of the controller. What I'm wondering here is if the stepper drivers function like the solid state relays I'm using in that the voltages involved are electrically isolated. If so, I can use higher voltages for the motors, power them individually, and therefor they won't lose torque at (relatively) high speeds. I'm running at 12mm/sec right now so the dam thing will at least make it through a print! Thanks for your interest noobman but I can't afford to fry more electronics right now. I don't have the electronics skills necessary to go forward with this.

Perhaps a better way to do this is with optocouplers. Some stepper drivers have optocouplers by default for the control signals. With such a device then yes you can use different psu because the control signals are galvanically isolated from the driver, the information is sent as light, but otherwise the two circuits have nothing with each other. The two circuits are only coupled by light. So i think opto isolator could be used on the step/dir/en lines, it converts one side to light, than to whatever voltage is on the other side. This is much better option imho than other hacks. Although ssr internally kinda do the same thing, e.g. convert to light to "couple" the circuits, probably wont work at the speeds that board does, e.g. for step signals.

Edited 1 time(s). Last edit at 05/31/2013 03:53PM by NoobMan.