Thermostatic Fan Control

  • HI Everyone,

    I have a question regarding thermostatic fan control. I have two fans that are PWM controlled that cool my board and power supply. Currently I have then mapped to the MCU and driver on the Duet and drivers on the Duex. One thing I have noticed is that when the fans kick in (40 degrees Celsius) they kick in which is fine, and they seem to turn off when the MCU temp gets to 39 degrees. Is there anyway you can adjust the temperature they kick off at? I would like to get them going for a bit longer to drop the MCU temp down so they don't have to start as often (Say 35 degrees).

    Kind Regards,

  • @samlogan87 If I understand you correctly, you want to increase the hysteresis from 1 degree to 5 degrees or thereabouts. So the fan comes on when the temperature gets to 40 degrees but will stay on until the temperature drops to 35 degrees C, yes? If so, I don't think that can be done. But there is way to do something similar.

    If you use the format T35:40 in your M106, then the fan will cycle from zero PWM at below 35 degrees to full PWM at 40 deg C and above.

    You can also use the "L" parameter to set the minumum fan speed. If you set it to 255, this will force any non-zero PWM value to be 255 - effectively fully
    on. But that would simply turn the fan on fully at 35 deg C which isn't what you want.

  • You could use a long blip time. If your fan needs 40seconds to go from 40 to 35deg, you could set the blip time to 40s. When the themperature hits 45, the fan will turn at 100% for 40s.

    This isn't what you want, but it could do nearly the same thing. This not a nice and clean way to do it, by the way...

  • Moderator

    I think Deckingman has the right solution. Set the min fan speed to something low so that it's constantly running at a slower speed. The board should probably be getting cooled during the print anyway. If you can find a good low speed set point you can maybe avoid the constant off and on cycle.

  • I just run fans all the time, wired to the power supply. Why wait until the things gets hot to turn on the fan? If you object to the noise, run the fan at a low voltage. I have a 208VAC fan blowing slowly (117VAC in) and quietly across the controller board as long as the machine is powered up.

    Turning on a fan after things have heated up seems a bit like closing the barn door after the horses have run out.

  • @deckingman @Phaedrux yes correct. I thought it wasn’t a customisable parameter so that’s fine. Hopefully when conditional g-code gets released it might be something that can be done. I may have a play around with how low I can run the fans. They are proper pwm fans so I maybe able to run them really low to the point they are circulating air but are almost inaudible. Currently they start at 0.3 at 40 and ramp up to 1 at 65 degrees.

    @mrehorstdmd i would hardly call 40 degrees hot. I have gone to great lengths to make my printer almost silent (watercooling, air pump for part cooling) so having a 80mm fan running constantly is annoying. I currently don’t have an office so it sits in the lounge, which annoys the wife when it’s running.

    Kind Regards,

  • @samlogan87 As well as the "L" parameter, there is also the "X" parameter which will limit the maximum fan speed. It might be worth having a play around with that to see if you can get adequate cooling at a lower (and therefore quieter) speed.

    BTW - do you have any details of the air pump you are using for part cooling.? It's something I am considering doing and I've been looking at pond air pumps but noise level data is a scarce.