I ran into an issue where once I connect the 3rd wire (techometer) the fan will get a constant 20.4v making it hot to the touch and smelly. This voltage is supplied even if the hotend is cold.
I connected the 2 pins to the FAN 1 header and the 3rd PWM wire to the Z-endstop PC2 pin.
It seems that no matter which PWM pin I choose, I either get ADC error min/max temp out of range or this constant 20.4v to the fan while it’s not spinning.
Is there any other way I can kill the heaters if there’s a fan failure of the temp near the heatbreak is rising?
If you only have a 3 pin PWM fan then there is no RPM signal and I doubt you can monitor RPMs in this way.
My CoreXY uses a 4 pin PWM fan with tacho signal and is configured like this on a BTT SKR2:
[fan]
pin: !EBBCan: PA0
enable_pin: PB3
cycle_time: 0.01
kick_start_time: 0.200
shutdown_speed: 0
hardware_pwm: false
tachometer_pin: ^EBBCan: PB7
tachometer_poll_interval: 0.0005 # will support up to a 30.000 RPM fan with 2 pulses per rotation.
If you only have a PWM fan then try different cycle times and if your board supports it hardware PWM.
Would also be nice in any way to have your klippy.log attached!
What exact fan are you using?
Hey there sorry for digging this thread up but I have the exact same setup and the exact same question:
@terra said that you need to put a diode in between the tacho-output and the tacho-pin, but what kind of diode? Do I not need a step down module 127V → 3.3V?
Also I had the issue that the PWM control didn’t seem to change the output voltage and therefore the actual rpm, any ideas why this might be the case?
@EddyMI3D I know what PWM does but by changing the pulse width it lowers the effective voltage. But that was not my point. The point was that the actual rotation of the fan didnt change for different %-levels that I changed in Klipper.
Also normally if one would measure the voltage of a PWM driven output, the multimeter (or at least my multimeter) shows a ever changing value since it can’t keep up with the speed of the changing voltages.
In this case my multimeter showed a steady 12V output.
Could it be that this is the case because I put a step down converter between the fan and the output pins on the mainboard (the output is 24V)? I read somewhere that the PWM is realized by the GND pin, so maybe I need to plug the GND of the fan directly into the mainboard and only run the VCC pin through a step down module?
To your second question:
I want to get a tachometer signal to my motherboard, so I need to plug the cable into my mainboard somewhere. But the signal coming from the fan should have the same voltage as the operatin voltage of the fan which is 12V. The logic of the SKR Mini E3 v3.0 is running on 3.3V and as @terra already said, just plugging it in may damage the mainboard.