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    24V Pump - can I connect direct?

    Duet Hardware and wiring
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    • benkay
      benkay last edited by

      Hi,

      I've seen mixed reports on whether a 24V air pump can be wired directly to a Duet VIN Fan Header, or not.

      The specs ripped from the product description are :

      Rated voltage: 24V
      No load current: 400MA
      Recommended supply : 24V 2A (needs sourcing)

      Some confirmation would be good if I can wire direct, or if I need some sort of relay/power expander.

      Thanks, Ben

      1 Reply Last reply Reply Quote 0
      • dc42
        dc42 administrators last edited by

        The main issue is likely to be the starting current. Measure the DC resistance of the pump several times, turning the rotor slightly between measurements, and take the lowest measured value. If it's less than 8 ohms than the starting current would exceed 3A, in which case you should connect a suitable thermistor in series with it to reduce the starting surge. Here's an example of a thermistor that may be suitable: http://uk.farnell.com/epcos/b57153s0330m000/thermistor-ntc-33r-1-3a/dp/1688797.

        Hergonoway 1 Reply Last reply Reply Quote 0
        • benkay
          benkay last edited by

          OK, I've been recommended a reprap Power expander which I understand opto-isolates the Duet board.

          Presuming resistance is >8 ohms, or I put a thermistor in series, is there then no risk to the duet board? I'd prefer to wire it direct, simply to reduce the wiring mess needed for the power expander.

          1 Reply Last reply Reply Quote 0
          • kraegar
            kraegar last edited by

            I recommend an opto-isolator based on my own experience and killing a fan port.

            1 Reply Last reply Reply Quote 0
            • dc42
              dc42 administrators last edited by

              The only risk I can see is that if the pump stalls for an extended period of time (e.g. because the pump mechanism seizes up) then the mosfet and the thermistor (f you have one) may overheat - but the motor will probably burn out too.

              1 Reply Last reply Reply Quote 0
              • Hergonoway
                Hergonoway @dc42 last edited by Hergonoway

                @dc42

                Based on your recommendations, is the schematic below the right one for connecting an air pump directly to the Duet ?

                alt text

                1 Reply Last reply Reply Quote 0
                • dc42
                  dc42 administrators last edited by dc42

                  Yes it is. The flyback diode is optional if the Duet is revision 1.02 or later, but having one close to the motor will help to reduce any interference generated when you PWM the motor.

                  1 Reply Last reply Reply Quote 1
                  • SM3D
                    SM3D last edited by SM3D

                    @dc42 and @benkay just wanted check with both of you my wiring before connecting to my duet 1.01. I followed the post and wired the pump accordingly. Here are the pictures:

                    0_1527328363356_20180526_113737.jpg

                    0_1527328376989_20180526_113747.jpg

                    Please let me know whether it is correct or not. I surely do not want to blow my Duet.

                    Cheers,
                    Vasan

                    Hergonoway 1 Reply Last reply Reply Quote 0
                    • Hergonoway
                      Hergonoway @SM3D last edited by Hergonoway

                      @sm3d seems correctly set

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                      • SM3D
                        SM3D last edited by

                        Thanks @Hergonoway will update whether berd air is effective or not

                        Cheers,
                        Vasan

                        Hergonoway 1 Reply Last reply Reply Quote 0
                        • benkay
                          benkay last edited by

                          Looks correct to me...although I understand that the later boards have the diode in-built so not strictly necessary to add one there.

                          1 Reply Last reply Reply Quote 0
                          • Hergonoway
                            Hergonoway @SM3D last edited by

                            @sm3d In my case, putting the thermistor didn't closed the circuit as it should, so for now and until @dc42 finish his tests regarding what should be used I don't use the thermistor. For info I'm running the air pump MAX in 24v sold by makerhive.

                            1 Reply Last reply Reply Quote 0
                            • SM3D
                              SM3D last edited by

                              @Hergonoway I have trouble running the pump with thermistor from PWM controlled fan ports but I could run them with always on fan ports. Here is my post about it:

                              https://forum.duet3d.com/topic/5449/not-able-to-pwm-for-berd-air-pump/10

                              I even shorted the legs of thermistor and tried from PWM fan ports but no luck. If you have any ideas please post it.

                              Cheers,
                              Vasan

                              1 Reply Last reply Reply Quote 0
                              • BenDiesel
                                BenDiesel last edited by

                                So I have a 24v berdair hooked directly up. I usually run at 25 to 30% and have the Pam set to 255khz.
                                The motor get rather warm. Almost to hot to tuch. Should I be concerned?

                                1 Reply Last reply Reply Quote 1
                                • Hergonoway
                                  Hergonoway last edited by Hergonoway

                                  255K is way to high try 25K (F25000). In my case the sound and the temp dropped a lot.

                                  Note that I've directly connected the 1/8" ID Tygon tube to the metal tube, it reduce pressured area and reduce heat from the pump mechanism (the white plastic part)

                                  1 Reply Last reply Reply Quote 1
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