Wiring two 4pin PWM Fans



  • Hi all,

    first of all I just want to say that I really like your Duet3D Wifi board, its greate to use and much better than my UltiBoard 2.1.4 before. So greate work!

    I have a question about wiring two 4-wire pwm fans (Noctua) together that I can controll them both at the same time at Fan0. Regarding to this thread

    https://www.duet3d.com/forum/thread.php?id=3947#p34601

    I got some instructions how to do. I connected the two 12V fans in serie and pluged them in one of the "alwas-on" fan connector. That works fine, but without any pwm control of course. Then tried to connect both 5v+ pwm wires (one from each fan) paralell and put it in Fan0, so for right and left object cooling. Unfortunately, that didnt work. They started at 100%, but when I reduce the speed to about 80%, then one of them just stopped.

    So my target is to put the two pwm fans together that I can controll both fans with the same pwm signal from F0. Acctualy like at hardware stuff, where you have e.g. the possibility to take a Y-adapter and then you are able to control two 4pin pwm fans at one 4 pin header.

    I dont have much knowledge about electronics, but maybe one of you guys can give me a shot how I could do that.

    Fan info: https://noctua.at/en/products/fan/nf-a4x20-pwm/specification

    sen



  • If I got it right you have 24V PSU so you put the fans in series. But you have no chance to make PWM control from a single signal in this configuration without quite a fancy level translator circuit. So your best solution would be like in the last post of thread you gave the link on. You should use a 24V-12V DC-DC converter. Connect its input to your PSU output and its output to power and ground pins on your fans in parallel (yellow and black wires at fan connector). Then you can connect PWM control pins of the fans to FAN0 on DUET board (or any other which are convenient for you) in parallel. This configuration should work and control fans' speed down to 20% according to datasheet.
    ADD: You can try to use series connection of the fan but leave the pwm pins unconnected and connecting power supply pins of the fans to fan connector on Duet board. Then you can use standard pwm mode of Duet firmware. I don't know if noctua's fans would be speed-controlled in this configuration.


  • administrators

    As the previous post says, to use the PWM wire you will have to connect the + and - fan wires from the fans in parallel not series, to a 12V supply which has a common ground with the supply to the Duet. Also you should increase the fan PWM frequency to 25kHz.



  • I have tried it yesterday, works perfect. Thank you for your help! 🙂



  • What is the configuration that works for you? Parallel connection with 24V-12V DC-DC converter or a series one without PWM pin? Just want to know if noctua's fan is working if controlled by PWM of supply voltage.


  • administrators

    I don't advise connecting multiple fans in series, because there is no guarantee that they will divide the voltage equally, especially if they are mounted in different ways so that one experiences greater resistance to air movement than the other.



  • @dc42:

    I don't advise connecting multiple fans in series, because there is no guarantee that they will divide the voltage equally, especially if they are mounted in different ways so that one experiences greater resistance to air movement than the other.

    Me too, I just would like to know if noctua's fans can be controlled by supply voltage PWM to use them with 12V power as they are very low noise and long lasting fans.



  • I have tried to control the noctua fans when they were only plugged in with 12V, but it didnt work.

    My solution was that what you both recommended, to get a 24V-12V DC DC converter for the 12V fans and wired them parallel. Then I wired the two 5v+ pwm parallel and plug them in Fan0 and that works greate.

    Indeed, fans are really silent and have some more benefits , also it works to control them from 20 to 100%. I used a bigger version for radiators of my watercooled pc system where you need high pressure fans and that is the reason why I have chose it for my printer.



  • Thanks for your info!


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