More info on higher voltage stepper mod?



  • Re: Higher input voltages for steppers

    Picked up a duet3 a couple months ago, have been running it in a printer a bit but the real reason I got was to replace grbl on my cnc ( for 5 axis in the, hopefully, near future ). Currently I run 48v on a dual Y axis cnc with a moving gantry and single X and Z motors which I obtained from OpenBuilds a couple years ago
    Just wondering if anyone has actually attempted the >=36v mod on the duet 3?

    I have a serviceable understanding around electronics and have done a lot of soldering and what-not in past, however I'm certainly no electrical engineer ( went software for the career for better or worse 😉 ) Anyways, if someone could chime in that's make me feel a bit better.

    Here are the highlights from the previous thread to save you a min:

    From @dc42 comment

    • The limiting components are the 5V regulator (AOZ1284) and the 12V regulator (TS30041) which are rated to 40V. Some of the capacitors in the 5V and 12V regulator circuits may be rated to 35V only, although I know that we often use 50V capacitors there.

    • You can manage without the 5V regulator if you provide external 5V power, however 12V is needed for the TMC5160 driver chips.

    • Probably the simplest way to allow up to 48V would be to remove diode D3 and feed between 12V and 30V to the pad that the cathode was connected to, to power the 5V and 12V regulators.

    • To go higher than 48V, you would need to replace the six 220uF 50V electrolytic capacitors.

    From @nomad comment

    • I think the AOD4184A mosfet and the Schottky CDBA540-HF would not be able to work above 40 volts, so the solution of removing the D3 diode and externally powering the regulators can be dangerous. It is right?

    So basically?

    1. Remove diode D3
    2. Get a 12 - 30v buck converter, wire into the 40+V powersupply, buck converter output goes to diode D3's cathode
      - Suppies power to 12 and 5v regulators, powers TMC5160 and 5v for power to rPi
    3. Need to double check capacitors on board to see if they are rated for the voltage?
    4. Given the last comment, cannot use "AOD4184A mosfet and the Schottky CDBA540-HF" which isn't a huge deal, since it's a CNC, although would be nice to have if it's a low effort change to get the heater outputs working in the 40+v setup

    Thanks to any help/reassurance ahead of time!


  • administrators

    • You should also consider adding a diode between the buck regulator and where the cathode of D3 was connected, in effect to replace D3. Its purpose is to prevent back-feeding from the 5V and 12V supplies into the source, which could blow the regulators.
    • You must not connect anything to the heater outputs, or you will blow the AOD4184A
    • You should remove the CDBA540-HF flyback diodes that are connected to the OUT1/2/3 heater outputs, otherwise if you ever turn on the heater outputs by mistake, you will subject them to 48V and they are only rated for 40V
    • The flyback diodes on OUT4-9 are also rated at 40V, so you must set the two VOUTLC voltage select jumpers to the 12V position, or remove them entirely
    • The 220uF electrolytic caps are probably all rated at 50V, but please check them. Using a 48V supply, there is a real risk that when you disable the motor drivers, the inductive energy fed back into the supply will cause it to exceed 50V. So I suggest you turn the 48V supply down a little.

    That's all I can think of. Do this at your own risk! Thanks to those who pointed out the issues with the AOD4184A and CDBA540-HF.



  • @dc42 Thank you for this, what a great breakdown and exactly what I was hoping to get. Hopefully it'll be helpful for others looking to do the same in the future. The additional diode, removing the flybacks and jumpers I honestly would have missed I'm sure.

    Hopefully I can get some time to give this a run and update. ( understood, at my own risk 😉 )


  • administrators

    FWIW we are considering revising the Duet 3 design to rate it to 50V. At the same time we would reduce the rated current of the 5V output and remove the option to power a Pi from it.



  • @dc42 A worthy sacrifice imho, thanks for the heads up.


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