Duet2 Stepper Driver Current Limit



  • I read on an old thread that the current limit for the stepper drivers was increased after implementing some changes in RRF to keep the driver cooler.

    Purely out of curiosity I would like to know if there are any more changes planned/possible to further increase the driver's current limit.


  • administrators

    Probably not. In theory, if I could implement standstill current reduction then we could increase the current some more, perhaps to 2.8A. Unfortunately the TMC2660 doesn't handle it automatically, and implementing it in firmware in a way that is totally reliable is difficult. I guess it might be possible to increase the current just in the middle section of high-speed moves.



  • @dc42 is the 2A driver limit (and config setting number) peak per coil at a full step position, or RMS?


  • administrators

    The limit is 2.4A (increased from 2.0A some time ago) and it is the peak value per coil.



  • Hi,
    just doing research on this "old" topic: With heatsinks on top/bottom of the driver and/or active-cooling it could be experimentally increased another 0,2-0,4A up to those 2,8? (Just thinking out loud here...)


  • administrators

    @lb said in Duet2 Stepper Driver Current Limit:

    Hi,
    just doing research on this "old" topic: With heatsinks on top/bottom of the driver and/or active-cooling it could be experimentally increased another 0,2-0,4A up to those 2,8? (Just thinking out loud here...)

    You could recompile the firmware to allow 2.8A, but it would be at your own risk.

    The point to remember is that Trinamic allows a higher current when the stepper motors are moving above a certain minimum rate than it does at standstill, because when the motor is moving, the heat dissipation is shared between all 8 mosfets instead of being in just 2 of them. Also the mosfets are on separate dies from the controller chip in the TMC2660, so the over-temperature detection on the controller chip won't react instantly to an overheating mosfet.

    I originally hoped to implement standstill current reduction in firmware, but that turns out to be very difficult to do in a way that is 100% reliable.

    Duet 3 will allow higher currents, certainly over 3A and maybe as high as 4A.


 

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