Steppers on 24V and both permanent fans and pwm fans on 12V ?



  • Hi there.

    I would like to feed my stepper motors with 24V , but my hotend fan (permanent on) and part cooling fans (pwm) are all 12VDC

    I will have 1 hotend fan and 2 PWM part cooling fans.

    Is this possible somehow on duet ? Can the fans run on another voltage than the steppers or do I need to do strange tricks there?

    For info: The cartridge heater in the hotend is also 24VDC

    I searched on google and found multiple posts where it is mentioned that duet has dual power supply possibility and than duet switches to ground etc, but I didn't really find a page with the info about it. For example some basic connection diagram or whatever.

    So I do want to connect :

    1. All stepper motors on 24V

    2. All fans (1 always on and 2 pwm) on 12V . (but these 2 pwm fans may run in parallel)

    3. Heated bed will be 230vAC through a SSR

    4. Heater cartridge is 24V

    5. I don't know if my endstops (optical) can run on 24VDC

    Kind regards,
    Bart


  • administrators

    You would need to remove the V_FAN jumper and feed +12V into the centre pin of that jumper block. Then all the fans will get 12V. But fans are cheap, so why not just buy 24V fans?



  • Because the fans I'd like to buy are not available in 24VDC version 😞 . (at least not easily available in my shop)

    Maybe just a small follow up question, but the 2 PWM fans will actually run on the same PWM speed. Couldn't I then just wire them in series on a 24VDC output of the duet ethernet ?

    For the permanently on hotend fan I could do with direct wiring and let that one just pass the duet (give it a small PSU on its own)


  • administrators

    The problem with putting two 12V fans in series and running them from 24V is that they are not guaranteed to share the voltage easily, so one may end up getting much more than its rated voltage, especially if the other one jams. This is why I don't advise doing it.

    24V fans are widely available on eBay as well as from the large electronic component distributors.



  • I bought some 24V fans. Like you said this is most probably the best way to do it anyway.

    Regarding optical endstops. I was hoping I could use endstops like these http://www.ebay.com/itm/Optical-Endstop-Switch-RepRap-Mendel-Prusa-RAMPS-v1-4-For-3D-Printer-arduino-WC-/221488349461?hash=item3391bc0115:g:h1YAAOSwTuJYrUyC

    They are made to work on ramps, but there is no specification about what voltage they will use.

    The DUET (ethernet) will be driven with 24VDC, but does this have implications for the endstops ? Or are these driven at another voltage anyway ?

    I read that they would work on 3,3V, so if I try my endstop with GND to GND, VCC to a 3,3 voltage supply and then measure the signal, if it works (reacts) then it should work with duet ?

    Kind regards,

    Bart


  • administrators

    Endstop switches are driven at 3.3V or 5V. The endstop connectors provide 3.3V on the centre pin. You may need to reduce the value of one of the resistors (the IR LED series resistor) on the optical endstop to get it to work reliably at 3.3V.


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