Controlling water pump and radiator fan



  • Hi All,
    Just to double check how to connect a water cooling pump and a radiator fan to the Duet Ethernet.

    Using a single hot end, one pump and a radiator with fan. Both the pump and fan are 12V and below 1.5A.
    I don't want to switch the fans over to 12V as the part cooling fans are still 5V.

    If running the pump all the time, I simply wire it into the 12V of the PSU.
    If running only when the hot end is active, I wire the + to the VIN and the ground to the GND pin of FAN0 and use

    M106 P0 T50 S1 H1

    to switch on the pump when the hot end temp rises above 50C.

    For the fan of the radiator, I do a similar thing.
    I have a thermistor measuring the temp of the water and when it goes above 45C I want the fan to switch on.
    The + wire goes to the VIN and the ground to the GND of FAN1. For the fan settings I use:

    M106 P1 T45 S0.5 H2

    This is assuming I connect the thermistor to the Heater 2 sensor (E1 connector) and want the fan to run at 50% of the speed.

    Is this all correct?

    One extra question, connecting to VIN, what is the best way to to do that? There is no pin available with 12V as far as I can see and shoving it in with the screw connectors is not very elegant.


  • administrators

    The water pump may draw a high starting current if it uses a brushed DC motor. if this is the case, then you should use either an external mosfet switch that can better handle the starting current, or a resistor or surge-limiting thermistor in series with the pump to reduce the starting surge.



  • Currently, I have it on a direct 12V external power supply.
    I noticed that when I switch it in, it starts up slowly.
    Does that tell you anything?


  • administrators

    @zesty_lykle said in Controlling water pump and radiator fan:

    I noticed that when I switch it in, it starts up slowly.
    Does that tell you anything?

    That could mean that it has slow-start built in. Measure the starting current, if you can.



  • On my crappy multimeter, it starts at 0.28 amps and settles on 0.3 amps.
    But I don't think my meter is quick enough to accurately measure the starting current. I will see if Brian can measure it.

    But at least the rest of the config is correct, yes?


  • administrators

    For the water temperature you need to set up a virtual heater, not use heater 2.


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