DRV8825 – Max vref?

New Home Forum Mostly Printed CNC – MPCNC Advice – MPCNC DRV8825 – Max vref?

This topic contains 2 replies, has 2 voices, and was last updated by  JKFL 3 months, 2 weeks ago.

Viewing 3 posts - 1 through 3 (of 3 total)
  • Author
    Posts
  • #99124

    JKFL
    Participant

    Greetings,

    yesterday I milled some particle / press board (Dunno what it’s called in english?) and experienced some difficulties. It was a board I had laying around and I wanted to run a test on it just to check the dimensions.

    I noticed that the pressed wood chips started coming off on its own while being milled, but didn’t care that much about it.

    30 min program, after about 20 minutes in its last cutting procedure, the X-axis started stuttering, resulting in step loss… I also experienced Step Loss on the Z-axis at the beginning. I searched for starting values considering vref back then, getting “0,7v for X/Y and 0.48v for Z”. After experiencing step loss in Z, I changed the vref to 0.7, which works fine now. But after yesterday I was wondering what I can do about that. My steppers are 2A steppers and one post from Heath (searched the forum for “max vref”, getting this link) he stated the following:

    So if your steppers are 1 Amp:
    VREF = 1A * 8 * 0.068 *0.9
    VREF = 0.4896VDC

    If your steppers are 1.5 Amp:
    VREF = 1.5A * 8 * 0.068 *0.9
    VREF = 0.7344VDC

    The DVR8825 stepper drivers have a much more simple vref formula:
    VREF = Current(A)/2

    So I was thinking: I should be able to set X/Y to 1V on Vref. I actively cool them with 2 25mm fans directly onto them while a 40mm blower sucks the warm air out of the case where the RAMPS is placed.

    Maybe some more infos on top of that:

    12mm mill (6mm one broke ๐Ÿ™ )
    2mm doc
    480mm/min X/Y movement
    about 20k RPM
    45% Stepover
    As I’m new to CNC milling, these are the starting values I started with. Any hints where to change something here are appreciated ๐Ÿ™‚
    #99133

    Ryan
    Keymaster

    12mm mill

    That is big!

     

    As for voltage, Best I could ever get reliably is 1.1V after that I would get random overheats. Yes you can get a tiny bit more power but it is diminishing returns in my opinion. Focus on your CAM, proper CAM is extremely low load.

     

    1 user thanked author for this post.
    #99577

    JKFL
    Participant

    Sorry for the late reply.

    Yeah, as the 6mm one broke I only had that one left. On top of that, there are not many cheap endmills for 6 or 8mm routers. I finally ordered a 3.175mm adapter thanks to a link I found in the forum. As soon as that gets here, I’ll be able to test smaller mills.

    Again, as I’m new to milling, I don’t want to waste 10-20โ‚ฌ per mill on my testruns. As soon as I get good and reliable results with cheap mills and get familiar with all the settings, I’ll have everything at hand to invest in good mills. ๐Ÿ™‚

    After two of my drivers burnt out on 0.7V (these were pretty old DRVs) I got a new package of 5 and started changing in pairs – So now I got 2 old DRV on X, 2 new on Y and 1 new on Z. The steploss occurred on X. I’ll get back to testing as soon as the new adapter is here.

    It’s good to know that the DRVs can take up to 1V in vref, this way if I run into further issues I can turn it up in 0.05v steps.

    Thanks again for your answer Ryan ๐Ÿ™‚

Viewing 3 posts - 1 through 3 (of 3 total)

You must be logged in to reply to this topic.