Ideal voltage for the stepper driver trimmer resistors

Hi,

I was measuring the voltages on my Monoprice Maker Select IIP. Image below shows what I got. I was wondering if these are the ideal voltages or if I should change them. I know there is a formula to compute these somewhere but I’m too lazy to google it (but not to make a picture of it)… hehe.

This may be related to this other post by santoitaliano but I wanted to post a picture showing exactly where I got them on the board.

Screen Shot 2020-10-11 at 9.47.25 AM

Hi Dave ,

I’m also to lazy to google this up, but my recollection was that .8v was a good voltage for the factory motors (i.e. driven at about 90% from max current). The voltages listed seem fine even if the X and E are a bit lower than that. I would leave them alone if you’re not having issues with the X or E motors as they will run cooler with the slightly lower voltages. If those motors are skipping steps, I would look at upping the voltage, or checking the axis/extruder to make sure there are no mechanical issues.

As a side note, I would not push the driver current past 1.5 A. The A4988ET are rated for 2 A, but I don’t think they would last long above 1.5 A with the tiny heatsinks, and lack of airflow in the printer base.

OK, was super bored and googled… Here is a link to a page with the formula for calculating driver VREF for desired current: https://3dprinterwiki.info/setting-the-stepper-current-on-the-melzi-board/

Thanks SilverSurfer,

I also found this one as I was working on something else. Overall, looks like my settings are fine.

Screen Shot 2020-10-22 at 5.23.53 PM

I bring here what @santoitaliano said some time ago:

I was under the impression the C17HD6039-06N is 0.39A and the C17HD40102-01N is 1.02A.

After asking Moons directly, it appears this is incorrect:

  • C17HD6039-06N (Z) - 1.2 A (Vref with 90% safety factor = 0.864V x 2 = 1.728V - this is above the 2A max current of the A4988 drivers)
  • C17HD40102-01N (X,Y,E) - 1.3 A (Vref with 90% safety factor = 0.936V)

Update:

With the original settings I posted above, I “most of the time” get a clogged nozzle about 45 minutes to 1hr of printing. I figured it was heat creep so I checked the heatsink fan. It was fine. So I was thinking that maybe the stepper motor was overheating?

SO I MODIFIED MY EXTRUDER TRIMMER RESISTOR VOLTAGE TO 0.700V. I guess that keeps my stepper from heating? I haven’t gotten any clogs so far. Longest printed item was about 8 hrs. No under-extrusion either.

I’ll keep this 0.700 volt setting for now since I intend to replace the stock extruder motor with a pancake motor soon.