12v Water Pump on a 24V System



  • Hi Everyone,

    I know this may have been covered off before but I just want to make doubly sure before I blow my board up or something silly like that. Basically, I am pulling a water cooling system out of an old computer and thought I would put it on my printer to keep the noise level down a bit more (Already have a Berd Air style pump setup that is virtually silent). The hotend fan I have is quite noisy. So I have purchased a V6 water cooling hotend from https://youprintin3d.de/hotendszubehoer/e3d/wasserkuehlung/792/water-cooled-heatsink.html. The issue I have is that it is hard to find 24v Pumps. All my PWM fans that I have for board cooling etc are 24V so I do not want to revert to 12V fans for everything. So the 12V pump I have pulled out will have to do.

    My plan is to have the pump thermostatically controlled off the same parameters as the old hotend fan (Starting when the hotend gets to 45 degrees). I then have another thermistor that will monitor the water temperature and via a virtual heater, will turn on the 24V PWM fan accordingly. I have also purchased a 12V power supply as well.

    My questions is how to wire it. I will be using the 3 PWM outputs on the main board (I have a Duex2 as well) for the 3 fans (1x Board, 1 x 24V power supply, 1 x radiator). My Berd Air setup runs off a heater output that has been remapped. I understand that the fan outputs are negative switching. Does this mean that I could go from the 12v power supply to the pump, negative of the pump goes to the negative of the fan output on the DueX2 and then I need to put another wire from the negative of the board or 24V power supply back to the 12V power supply. Or am I better to remap a heater output on the Duex2 for the pump? The pump is 10.8W. It is an older pump that will not be brushless so will I need to add a flyback diode as well to protect the input?

    Any help would be greatly appreciated.

    Kind Regards,
    Sam



  • Yeah, you can run 12v from the supply though the pump and to the negative of the fan output, and then connect the 12 and 24 negatives somewhere.

    It says the Duex has flyback diodes for the fan output as of rev 0.8. way bottom of the page https://duet3d.dozuki.com/Wiki/Duex2_and_Duex5_Features

    it also says they have a 12v regulator, you may be able to use ?



  • @bearer thanks for your reply. I will have a look at what revision my board is. It would be great if it does.

    I thought about this however, I didn't want to do it as if I blow up a fan mosfet on the main board, I can still shift it to run off the duex2



  • oh, if your primary goal was to run it off the main board it has flyback diodes as of revision 1.02.



  • @bearer I was alway planning on running the Water Pump off the Duex2 and I may do the radiator fan off it as well. Is it just the heaters that don't have the flyback diodes as I had to put one on my air pump when I put it in. I forget. It was a while ago



  • Correct, no diodes on the heater outputs, just the fans. But if you already have a diode put on the pump then its a non issue, connect it wherever you like.



  • @bearer

    Yeah that is for the air pump. The water pump doesn't one at the moment. I believe I have a spare somewhere. It is just under an amp running at 12V so I may use one of the heater outputs on the Duex2 to drive the water pump just to be safe.



  • Gotcha. two pumps, just to keep it simple:D

    Worried about the current on the fan output? Duex fan transistor is good for 4.4A and the Fan connector i believe is rated for 4A.



  • Yeap haha. Should make it a quiet printer which will be good. I have to have it in the lounge and the wife hates it.



  • @bearer

    Just referring to one of your replies, are the Duex fan mosfets rated that high (4.4A)?



  • according to schematic and datasheet https://assets.nexperia.com/documents/data-sheet/PMV40UN2.pdf
    (obviously you have to verify the power dissipation and junction temperature as well)


  • administrators

    We recommend that you do not run water pumps that used brushed DC motors from the fan outputs. This is because the starting current for a brushed DC motor is usually many times the running current, and will probably exceed the 4.4A rated current of the bed mosfet.

    If your E1 Heat output is free then you can use that to drive the water pump; but then you must use an external flyback diode.



  • Ok I will remap a heater on my Duex2 board and use that. Thank you @dc42



  • @dc42 said in 12v Water Pump on a 24V System:

    We recommend that you do not run water pumps that used brushed DC motors from the fan outputs. This is because the starting current for a brushed DC motor is usually many times the running current, and will probably exceed the 4.4A rated current of the bed mosfet.

    If your E1 Heat output is free then you can use that to drive the water pump; but then you must use an external flyback diode.

    Maybe add that to the warning about adding diodes to brushed motors in the wiki for completeness? (And good catch!)


 

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