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DC step Down & duet 0.85

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  • undefined
    Gaou
    last edited by 24 Nov 2021, 12:35

    Guys i need some advice .

    I am running two fans on my printer but one of them ( hotend one) is 12v while my whole system runs on 24v.
    So i thought to connect a dc step down converter to get 12v out of 24v. My thinking is to get this close to the mainboard in series with the fan, but i am not sure if this is a good idea as the whole delta eefector seems to get power from that always on fan pins.

    What do you think should i procced and the only problem will be the leds or apart from that i am gonna run into much problems.

    Thanks in advanced,
    Pavlos

    Delta Printer || Duet 0.85 || firmware 1.23

    Laser K40 || Duet 0.85 || Firmware 1.26.1 || Web 1.22

    1 Reply Last reply Reply Quote 0
    • undefined
      rjenkinsgb
      last edited by 24 Nov 2021, 12:57

      The simplest thing is just connect a resistor in series with the fan.

      Look at the fan rated current and use a resistor that drops 12V at that current.
      eg. If it takes 40mA, the ideal resistance would be 12(V) / 0.04 (A) = 300 Ohms.
      Minimum power rating = current x voltage so 12 x 0.04 = 0.48W
      Use at least double the power rating so it's not running excessively hot; eg. 300 Ohms (or 330 Ohms) 1W.

      If yours works out to something other than a standard resistor value, use the next higher one.

      Robert J.

      Printers: Overlord pro, Kossel XL+ with Duet 6HC and "Frankentron", TronXY X5SA Pro converted to E3D toolchange with Duet 6HC and 1LC toolboards.

      undefined 1 Reply Last reply 24 Nov 2021, 15:36 Reply Quote 0
      • undefined
        Gaou @rjenkinsgb
        last edited by 24 Nov 2021, 15:36

        @rjenkinsgb said in DC step Down & duet 0.85:

        The simplest thing is just connect a resistor in series with the fan.

        Look at the fan rated current and use a resistor that drops 12V at that current.
        eg. If it takes 40mA, the ideal resistance would be 12(V) / 0.04 (A) = 300 Ohms.
        Minimum power rating = current x voltage so 12 x 0.04 = 0.48W
        Use at least double the power rating so it's not running excessively hot; eg. 300 Ohms (or 330 Ohms) 1W.

        If yours works out to something other than a standard resistor value, use the next higher one.

        the fan doesn't give me the watts of amps. so i measured the resistance and i am getting 8.20Mohm.

        that makes me 12v / 1.5A = 8ohms and 18watt power rating ... am i doing something wrong here ?

        Delta Printer || Duet 0.85 || firmware 1.23

        Laser K40 || Duet 0.85 || Firmware 1.26.1 || Web 1.22

        undefined undefined 2 Replies Last reply 24 Nov 2021, 16:14 Reply Quote 0
        • undefined
          dc42 administrators @Gaou
          last edited by dc42 24 Nov 2021, 16:14

          @gaou you should connect the step down converter to VIN. Then connect the + side of the fan to the converter 12V output, and the - side of the fan to the negative pin of the Duet fan output connector.

          The only other part of the Smart Effector that gets power from the fan pins is the LED lighting, which is connected in parallel with the hot end fan.

          Duet WiFi hardware designer and firmware engineer
          Please do not ask me for Duet support via PM or email, use the forum
          http://www.escher3d.com, https://miscsolutions.wordpress.com

          undefined 1 Reply Last reply 25 Nov 2021, 19:44 Reply Quote 0
          • undefined
            rjenkinsgb @Gaou
            last edited by 24 Nov 2021, 16:17

            @gaou said in DC step Down & duet 0.85:

            am i doing something wrong here

            A brushed motor will read near dead short, an electronic / brushless fan would likely give an extremely high reading, neither of which relates to the normal running current.

            Without specifications, the only way to know the operating current is measure it while the fan is running on a 12V supply.

            Robert J.

            Printers: Overlord pro, Kossel XL+ with Duet 6HC and "Frankentron", TronXY X5SA Pro converted to E3D toolchange with Duet 6HC and 1LC toolboards.

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            • undefined
              Gaou @dc42
              last edited by 25 Nov 2021, 19:44

              @dc42 said in DC step Down & duet 0.85:
              you should connect the step down ...

              thanks David . thats what i did and it worked fine...

              @ rjenkinsgb
              24 Nov 2021, 18:17
              that is what i would do i just didn't have a ps at that moment. But what David advised work pretty well so i am moving on.

              thanks a lot for ur reply.

              Delta Printer || Duet 0.85 || firmware 1.23

              Laser K40 || Duet 0.85 || Firmware 1.26.1 || Web 1.22

              1 Reply Last reply Reply Quote 0
              • undefined dc42 marked this topic as a question 25 Nov 2021, 21:42
              • undefined dc42 has marked this topic as solved 25 Nov 2021, 21:43
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