Can't get fan to run at anything but full speed



  • I just got a duet wifi and so far I really like it.

    I'm trying to connect the fans right now, and the always on fan for my e3d was no problem, but getting the cooling fan to work is driving me nuts right now.

    I've got a 24v system, using the
    1.17e (2017-02-10) firmware,
    1.03 (ch fork) Server version,
    1.14a Web interface

    I've configured the fans as follows in config.g:
    ; Fans
    M106 P0 S0.3 I0 F500 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S1 I0 F500 H1 T45 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H1 T45 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

    When I power things up, the fan doesn't start at 30%

    When I give it the M106 Sxxx with xxx being anything but 255 the fan will not turn on.

    M106 S255 will give me full fan speed.

    M106 S128 F0 will make the fan pulse in 1/2 second increments

    M106 S128 F1 will make the fan pulse in 1/4 second increments

    Once I get to an F of 10 the fan will no longer run at all.

    I thought the F was the frequency of the signal going to the fan, and I'm not sure what is going on.

    Has anyone got any suggestions on what to do?

    Thanks


  • administrators

    Yes the F parameter is the PWM frequency. Ordinary brushless fans are not designed to work with PWM and it's surprising that so many do. But some fans don't work at all with PWM, including a 24V blower fan I bought to use as a print cooling fan.


  • administrators

    Yes the F parameter is the PWM frequency. Ordinary brushless fans are not designed to work with PWM and it's surprising that so many do. But some fans don't work at all with PWM, including a 24V blower fan I bought to use as a print cooling fan.



  • Ok, so my only option is to buy a brushed fan??

    Or is there a way to turn off PWM for the fan control.

    I'm coming from the RAMPS/Marlin world, and honestly I find it surprising that brushless fans don't work



  • I guess I'll try a low pass filter, I think I've got all the parts


  • administrators

    Most brushless fans do work with PWM even though they were not designed to. Based on what you have told me, I can assure you that other electronics and firmwares won't be able to drive that particular fan using PWM either. As I said, I have one particular fan that doesn't work with PWM, but I also have at least 5 fans that do. Some of them need the PWM frequency reduced to 100Hz from the default 250Hz.

    PC fans that are intended to be used with PWM have a separate 4the wire for the PWM control signal.



  • It worked fine on my Rambo board



  • @ncbob:

    It worked fine on my Rambo board

    In which case, I'd guess that if you set the frequency to the same as the Rambo board uses than it'd work on the Duet.



  • Yeah, the trick is figuring out what the PWM frequency is on the rambo board running marlin. I don't see it in Marlin anywhere and I can't find any documentation on the Ultimachine site or anywhere else.

    The F setting is only available in reprapfirmware, not in Marlin.



  • @dc42:

    Most brushless fans do work with PWM even though they were not designed to. Based on what you have told me, I can assure you that other electronics and firmwares won't be able to drive that particular fan using PWM either. As I said, I have one particular fan that doesn't work with PWM, but I also have at least 5 fans that do. Some of them need the PWM frequency reduced to 100Hz from the default 250Hz.

    PC fans that are intended to be used with PWM have a separate 4the wire for the PWM control signal.

    Sorry to hijack, but do you have any links to a decent blower fan 24v? I've bought 2 and they're both rated high, but perform like crap. They are nice and quiet though 🙂



  • @ncbob:

    Yeah, the trick is figuring out what the PWM frequency is on the rambo board running marlin. I don't see it in Marlin anywhere and I can't find any documentation on the Ultimachine site or anywhere else.

    The F setting is only available in reprapfirmware, not in Marlin.

    In that case, just play around with the frequency until you find something that works. PWM is what it says - Pulse Width Modulation and it's just a way of switching on and off quickly but also varying the ON time compare to the Off time. So there can't be anything unusual about the way that the Duet does it compared to how some other board does it apart from the switching frequency. You could also play around with the "B" parameter (blip time). If the fan kind of oscillates but doesn't actually spin, a quick blip is a like a kick start to get it going.



  • @deckingman:

    @ncbob:

    Yeah, the trick is figuring out what the PWM frequency is on the rambo board running marlin. I don't see it in Marlin anywhere and I can't find any documentation on the Ultimachine site or anywhere else.

    The F setting is only available in reprapfirmware, not in Marlin.

    In that case, just play around with the frequency until you find something that works. PWM is what it says - Pulse Width Modulation and it's just a way of switching on and off quickly but also varying the ON time compare to the Off time. So there can't be anything unusual about the way that the Duet does it compared to how some other board does it apart from the switching frequency. You could also play around with the "B" parameter (blip time). If the fan kind of oscillates but doesn't actually spin, a quick blip is a like a kick start to get it going.

    I've already played around with it from 1hz all the way up to 25000. At lower hz it cycles slowly until about 6 or 7 hz then it won't run at all unless the pwm is set to 255. at higher increasing hertz it won't start running until about 2000, and then at pwm settings of 250 or higher. Going to higher frequencies and it can start spinning as low as 200, but I think the speed is not really changing.

    If I get a chance I'll through my scope on it and see what's happening.


  • administrators

    Another option is to put a R-C filter in series with the fan so that the PWM gets smoothed out and you drive the fan with a variable voltage. Connect a resistor of between10 and about 200 ohms between the Duet fan output and the fan. Also connect a capacitor of at least 100uF in parallel with the motor.

    I find it very hard to believe that the same motor works with RAMBO. The RAMBO board has a flyback diode in parallel with the fan output, but apart from that it has nothing else that would make a difference.

    Standard Arduino PWM frequency is about 490Hz, but I don't know whether Marlin uses that or alters it.


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