Minimal effect of PWM for Hotend Fan

  • I found enabling pwm doesn't do much in reducing fan speed or led brightness.
    Even setting it to S2 or S0 reduces the speed only to about 80-85%.
    (S1 seems to be identical to S255)
    Note: I had to increase pwm frequency to 30khz to get pwm working, using default values the fan would stop at S253 or below.

    Is this expected behaviour, and is it save to operate the smart effector with these settings?
    M106 P1 S0 T0 F30000

    Actually i would like to use use thermostatic mode
    M106 P1 T70 H1:2 S0 F30000

    I want to reduce the fan speed because it runs at a resonance frequency and other than that i would be happy to neduce the fan noise.
    Something like 65 or 70% fan speed should be ok.

  • I'm really surprised at your PWM frequencies. I'd have thought that 30,000 is far too high. I control 8 different fans on my printer, ranging in size from 30 mm, 40mm and 60mm. All apart from the part cooling fan run in thermostatic mode. All of those run best at PWM of 250 with the exception of the 30mm fans which run through a 24 to 12v converter. For these to work with PWM, I have to drop it to 10 hz. Having said all that, all fans are different. Some work well with PWM and some don't but if I were you, I'd try lowering the PWM frequency rather than setting it really high.

    If you want to run in thermostatic mode, the "S" value is the maximum speed so for example some of my fans are configured thus:

    M106 P7 S255 I0 F250 H108 T40:50.

    Effectively this starts the fan when the temperature on H108 reaches 40 degC, ramping up to fully on (S255) when the temperature reaches 50 degrees C. At 45 degrees, the fan will run at half speed (equivalent to S127).

    Other fans are too noisy at full speed so for them, I limit the maximum speed to half by using S127. In this case, the fan will still start at 40 deg C but reach a maximum of half speed at 50 deg C. At 45 deg C, the fan runs at 1/4 speed (equivalent to S=64).

    Edit- You can also set a lower theshold. For example my hot end cooling fan is defined thus:

    M106 P1 S255 I0 L125 F250 H1 T60:140.

    What this does is turn the fan off below 60 deg c. At 60 deg C it will start at half speed. Between 60 and 140 deg C, the speed will be proportionally set between half speed (L127) and full speed (S255). Above 140 deg C, the fan is fully on. The effect of this is that it knocks a few seconds off the warm up time for the hot end without noticeably increasing the cool down time. It's a noisy fan so having it off all together at temperatures below 60 deg C is beneficial to me.

    Hope that makes sense.

  • I'm aware the S Parameter sets the maximum speed.
    Im already using the thermostatic mode but with pwm disabled (S255) which works fine:
    M106 P1 T70 H1:2 S255

    The fan immediatly stops when i drop below 10000 Hz and the full range down to S2 can be used only at 30000 Hz
    Its the standard E3D 30mm fan that comes with the E3D V6. Is this known to be an problematic fan when using pwm?

    Frequencies between 5 khz and 25 khz produce an really annoying sound and frequencies below 100 Hz result in annoying flicker of the leds on the smart effector.

    Some Ideas:
    The leds connected in parallel to the hotend fan may cause issues when using pwm by shorting the fan connectors.
    Other than that at 30 khz i suspect the minimim "on" time for pwm on the duet may just be too large to provide an effective pwm.

  • Just a short update:
    After replacing the 30mm e3d fan with a 40mm one, pwm works great at all frequencies.
    However still have to set the frequency to >20khz to not have either flickering LEDs or an anoying sound.


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