Suggestions for case fan setup on BigBox



  • Hi,

    I have two case fans on the BigBox. One blows on the electronics and the other is an exhaust fan at the back. Both have been controlled by a dual temperature controller and are of the 4 pin sort running 12V. PSU is 24V so I have a separate step-down for 12V.

    I have started the conversion to Duet Wifi + Duex5 and kept the controller but started to think more of controlling them from the Duet or Duex5. And as I can enable 12V regulator for the fan outputs I can get rid of the step down.

    Question, Can the Duet adjust fan speed by the case temperature yet? Or is it only on/off. How about CPU / Duet temperature or load through the stepper drivers?

    Options

    • Keep the original controller

    • Only use two wires and PWM from Duet (don't know if I can do this with 4-wire fans)

    • Use 3 wires and feed fans only the PWM signal. Then I need 12V constant from somewhere else.



  • Hmm, after some more digging I think I need to ditch the 4-wire fans if I want the Duet to control them.

    Found some specs about the PWM signal:

    • PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz

    • Absolute maximum voltage level: VMax = 5.25 V (open circuit voltage)

    http://www.formfactors.org/developer/specs/4_wire_pwm_spec.pdf


  • administrators

    Yes it's possible to use 4-wire fans with the Duet. Connect the red and black wires to +5V and ground, and connect the PWM control wire to the FAN- output pin of the controlled fan connector. Set up 25kHz PWM frequency and inverted polarity by sending M106 P# I1 F25000 where # is the controlled fan number. Optionally, connect the yellow tacho output wire to pin PB6 on the expansion connector.

    You can turn the fan on/off by case temperature if you use a thermistor connected to a spare thermistor input channel to monitor the case temperature. On the wish list is to control the fan using the CPU temperature sensor and the overheat warning in the TMC2660 drivers, also to make the PWM increase smoothly with temperature instead of just off or on at a fixed PWM level.



  • Awesome David!

    I'm really starting to like this controller and I haven't event fired it up yet 😄

    I thought 25kHz PWM would be asking too much.



  • @dc42:

    Yes it's possible to use 4-wire fans with the Duet. Connect the red and black wires to +5V and ground, and connect the PWM control wire to the FAN- output pin of the controlled fan connector. Set up 25kHz PWM frequency and inverted polarity by sending M106 P# I1 F25000 where # is the controlled fan number. Optionally, connect the yellow tacho output wire to pin PB6 on the expansion connector.

    You can turn the fan on/off by case temperature if you use a thermistor connected to a spare thermistor input channel to monitor the case temperature. On the wish list is to control the fan using the CPU temperature sensor and the overheat warning in the TMC2660 drivers, also to make the PWM increase smoothly with temperature instead of just off or on at a fixed PWM level.

    My Fans are 12V ans the main PSU is 24V. Is there any 12V regulator on the Duet Wifi or Duex5? Can't find any in the schematics.

    Is it enough to wire the fans to an external 12V source then the PWM to FAN-? What I have read of the PWM signal there should be a pull-up in the fan.

    How many tacho inputs can the Duet have?


  • administrators

    There is a 12V regulator on the DueX5 but not on the Duet. You can wire the fans as you say; or if all your fans are 12V, you can remove the fan voltage select jumper on the Duet and feed +12V to the centre pin of the jumper block instead.

    Schematics are at https://github.com/T3P3.


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