SOLVED 12v PWM water pump "Fan" on 24V Duet 2



  • Just doing a sanity check...
    I recently put one of these water cooled hotends on my 24v duet 2 wifi system.
    https://www.aliexpress.com/item/32850217541.html
    The pump is essentially a 12 volt 4 wire fan.
    All my other fans are 24v, so I'd rather not change all of them.
    To get it running I simply used a mosfet module triggered by one of the fan headers ( I have both a 12v power supply which I use for LEDS).
    The fan RPM wire is connected to PB6 and correctly displays the pump RPM when at full power, but of course not at other PWM levels.
    I'd like to correct that (even though I probably will never run at less than 100% PWM)
    If I read the docs correctly I should be able to wire it like this...

    +ve wire to 12v +ve on power supply
    -ve wire to 12v -ve on power supply
    RPM wire to PB6
    PWM wire to Fan header -ve

    This should allow me to do away with the mosfet and not have to worry about a buck converter should it not?

    I've replaced the very noisy 12v radiator fan with a 24v 4 wire fan as well.
    I plan to vary the fan speed dependent on the coolant temperature just to keep noise as low as possible.
    As I understand it, I can use an GPIO to read the RPM, but only PB6 is displayed in DWC.
    Is that correct?



  • For those interested, I got this working in the way I stated.
    As a bonus, both the water pump speed and the radiator fan speed are shown on DWC.

    For water pump
    +ve wire to 12v +ve on seperate power supply
    -ve wire to 12v -ve on seperate power supply
    RPM wire to PB6
    PWM wire to Fan header -ve

    For radiator fan
    +ve to always on fan +ve
    -ve to always on fan -1ve
    RPM to exp.e3.stop
    PWM to PWM fan -ve

    Pump & Fan config.g settings:

    ;water pump
    M950 F1 C"!fan1+^exp.pb6" Q25000                             ; create fan 1 (water pump) on inverted pin fan1 and set its frequency.  Set RPM to E3 stop with pullup enabled
    M106 P1 C"Water Pump" H1 L0.5 X1 B1.2  T50:60                       ; set fan 1 name and value. Thermostatic control is turned on.  Monitoring hotend sensor
    
    ; water temp monitor & fan
    M950 F5 C"!fan2+^exp.e3_stop" Q25000                                        ; create fan 2 on pin fan2 and set its frequency.  Use e3.stop with pullup for RPM
    M308 S5 P"e1temp" Y"thermistor" A"Water temp" T10000 B3950  					; Configure Water temp sensor
    M106 P5 C"Radiator_Fan" H5 L0.3 X1 B1.2  T30:34    	; set fan 4 value, turn on at 30% if the water temperature reaches 30, and increase to full speed gradually as the temperature rises to 34C
    
    


  • @OwenD Just doing a sanity check...

    You failed, sorry ....

    Use a 12V converter

    Don't know about your related questions.



  • @OwenD said in 12v PWM water pump "Fan" on 24V Duet 2:

    +ve wire to 12v +ve on power supply
    -ve wire to 12v -ve on power supply
    RPM wire to PB6
    PWM wire to Fan header -ve

    That's what the manual says.
    But the question is, will the PWM_in pin accept 24V pulses? And will the Duet survive a 12V RPM signal on PB6? The manual doesn't specify the RPM output level, nor the required PWM input. Maybe both are 5V?
    The only option is to test the pump with security in your mind. Set the Fan header to 5V (for testing) and let the pump spin. Don't connect the RPM pin. Then read the output voltage of the RPM-pin. (Oscilloscope preferred)

    @jens55 said in 12v PWM water pump "Fan" on 24V Duet 2:

    Use a 12V converter

    Doesn't help at all, when there are additional pin voltages to consider...



  • @jens55 said in 12v PWM water pump "Fan" on 24V Duet 2:

    Use a 12V converter

    Doesn't help at all, when there are additional pin voltages to consider...

    Which is why I specifically indicated that I was only commenting on sending 24V to a 12V fan!



  • @jens55
    No SIr. The original fan is powered by the pump-powersupply. And he said, he'll replace it with a thermostatic controlled 24V fan.



  • @jens55 said in 12v PWM water pump "Fan" on 24V Duet 2:

    @OwenD Just doing a sanity check...

    You failed, sorry ....

    Use a 12V converter

    Don't know about your related questions.

    Wow, thanks for your insightful and carefully crafted explanation.
    It's the ability to get such detailed information from the experts that makes this forum great.

    @o_lampe
    My logic was based on the fact that the pump motor is essentially a four wire fan in design and therefore requires constant 12 volts on +/- and a pwm signal for speed.
    Where that 12 volts comes from should matter not aside from if a common ground is required.
    On further searching I found this document which appears to support my hypothesis.

    https://railcore.org/customization/12v_fans.html

    With regards to PB6, it wouldn't be a question if I was using a 24v fan, so it's unlikely 12v will do any damage if indeed the rpm signal ever gets that high.

    As for the pwm signal to the pump, I must admit I'm unsure. The specs on the fans I looked at say the pwm input is typically 5v.

    The radiator fan is completely separate and is 24v.
    My only question there is in relation to reading the rpm.



  • I am glad I could be of help even though you do not appreciate my input. I hope that other people reading this will get the gist that it is not a good idea to hook a 12V fan to a 24V power supply.
    If in fact you were going to run the fan on 12V, then you did not make this fact clear. Yes, on re-reading one can interpret it that way but then why ask about a 12V fan on a 24V duet?
    Anyway I am done with this thread.



  • @OwenD
    Even if it's a 5V signal from the 4-pin devices, some pins on the Duets only survive 3.3V.
    You can make a voltage-divider from resistors, because it's only a one way signal.
    It would be worse if you could only send 3.3V on the PWM pin. It might work, but I wouldn't rely on it.
    In that case you'd have to use a level-shifter daughter board.
    Better check the Duet schematics.



  • For those interested, I got this working in the way I stated.
    As a bonus, both the water pump speed and the radiator fan speed are shown on DWC.

    For water pump
    +ve wire to 12v +ve on seperate power supply
    -ve wire to 12v -ve on seperate power supply
    RPM wire to PB6
    PWM wire to Fan header -ve

    For radiator fan
    +ve to always on fan +ve
    -ve to always on fan -1ve
    RPM to exp.e3.stop
    PWM to PWM fan -ve

    Pump & Fan config.g settings:

    ;water pump
    M950 F1 C"!fan1+^exp.pb6" Q25000                             ; create fan 1 (water pump) on inverted pin fan1 and set its frequency.  Set RPM to E3 stop with pullup enabled
    M106 P1 C"Water Pump" H1 L0.5 X1 B1.2  T50:60                       ; set fan 1 name and value. Thermostatic control is turned on.  Monitoring hotend sensor
    
    ; water temp monitor & fan
    M950 F5 C"!fan2+^exp.e3_stop" Q25000                                        ; create fan 2 on pin fan2 and set its frequency.  Use e3.stop with pullup for RPM
    M308 S5 P"e1temp" Y"thermistor" A"Water temp" T10000 B3950  					; Configure Water temp sensor
    M106 P5 C"Radiator_Fan" H5 L0.3 X1 B1.2  T30:34    	; set fan 4 value, turn on at 30% if the water temperature reaches 30, and increase to full speed gradually as the temperature rises to 34C
    
    

  • Moderator

    @OwenD Well done.


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