[BUG] BTT SKR Mini E3 V3.0 and FAST_PWM_FAN_FREQUENCY

[unitrix0]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

I wanted to reduced the noise from my part cooling fans when not running on 100%. So I enabled FAST_PWM_FAN, but to what ever value I set FAST_PWM_FAN_FREQUENCY, the fans wont even turn on anymore. I've tried 125490, which I think would be calculated value for my board and 25000. And since I run 12V fans I set FAN_MAX_PWM to 110.

I have also found this older bug report but I'm not sure what the conclusion is. Is it not possible to do this with this board?

Bug Timeline

No response

Expected behavior

Setting the PWM frequency by enabling FAST_PWM_FAN and setting FAST_PWM_FAN_FREQUENCY

Actual behavior

The fans don't even turn on with 100% fan speed.

Steps to Reproduce

No response

Version of Marlin Firmware

Marlin bugfix-2.1.x (Sep 3 2023 12:41:13)

Printer model

No response

Electronics

BTT SKR Mini E3 V3.0

Add-ons

No response

Bed Leveling

UBL Bilinear mesh

Your Slicer

Cura

Host Software

OctoPrint

Don't forget to include

• [X] A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

Configurations.zip

[ellensp]

running 12v fan on 24v will not work long term

You still sending pulses of 24v to a 12v device (its not just a restive load, this works fine on a heater)

Also setting FAN_MAX_PWM to 110 is also wrong... if your trying to limit the power (if it was just a restive load)

to get equivalent to power you need 1/4 ie FAN_MAX_PWM 64

power = voltage * current

so for a 12ohm fan (just for simplicity of the example) at 12v it will draw 1 amp. so that is 12watts at 24v it will draw 2 amps, so that is 48watts

ie 4 times the wattage, so to keep the same wattage you need 1/4 duty cycle , not approximately half

[unitrix0]

Strange, for a moment I felt like I should never ever touch anything in my Marlin configuration again...

Anyways, I had the old 24V fans still laying around. So I commented out FAN_MAX_PWM and tried it again with FAST_PWM_FAN_FREQUENCY = 25000. Now the fans work when speed set to 100% but anything lower they stand still.

[ellensp]

why did you ignore the warning?

Marlin/src/module/temperature.cpp: In member function 'void Temperature::init()':
Marlin/src/module/../inc/../../Configuration_adv.h:646:34: warning: unsigned conversion from 'int' to 'uint16_t' {aka 'short unsigned int'} changes value from '125490' to '59954' [-Woverflow]
  646 |   #define FAST_PWM_FAN_FREQUENCY 125490  // Define here to override the defaults below
      |                                  ^~~~~~
Marlin/src/module/temperature.cpp:376:64: note: in expansion of macro 'FAST_PWM_FAN_FREQUENCY'
  376 |   #define SET_FAST_PWM_FREQ(P) hal.set_pwm_frequency(pin_t(P), FAST_PWM_FAN_FREQUENCY)
      |                                                                ^~~~~~~~~~~~~~~~~~~~~~
Marlin/src/module/temperature.cpp:380:47: note: in expansion of macro 'SET_FAST_PWM_FREQ'
  380 | #define INIT_FAN_PIN(P) do{ _INIT_FAN_PIN(P); SET_FAST_PWM_FREQ(P); }while(0)
      |                                               ^~~~~~~~~~~~~~~~~
Marlin/src/module/temperature.cpp:2858:5: note: in expansion of macro 'INIT_FAN_PIN'
 2858 |     INIT_FAN_PIN(FAN0_PIN);

First thing is our tying to set to high a fan frequency 125490, but it is being truncated down to 59954 this has a maximum value of 65535

reduce this value to acceptable levels.

[unitrix0]

why do you not read my comments completely?

[ellensp]

also did you see "Setting very high frequencies can damage your hardware." ?

did you look at the specification of the mosfet to check it can actually do this high speed without burning?

Started with provided config files... you got this HUGE warning and you didnt even mention it...

[unitrix0]

...tried it again with FAST_PWM_FAN_FREQUENCY = 25000.

[unitrix0]

don't know what you're trying but it's not gonna work.

[github-actions[bot]]

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