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How big a 5v power supply needed for Duet 3 and RPI4?

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  • ?
    A Former User @N7JTI
    last edited by 17 Sept 2020, 17:00

    @N7JTI said in How big a 5v power supply needed for Duet 3 and RPI4?:

    3A that are apparently needed for the RPi 4?

    you don't need the full 3A if you're not going to add USB devices that also draw current from the Pi supply.

    Is there some other pin or connector for me to insert it on?

    you can supply 5v to pin 2 and 4 on the 40 pin gpio header if you build a custom cable f.ex.

    the most important thing is to avoid voltage drop in the pi supply, or use a adjustable 5v source so you can account for the loss and have 5v with margin at the pi.

    I'm planning on using a dedicated 5v supply, custom ribbon cable 5v --> Pi --> Duet and setting the 5v supply to 5.5v or whatever so I can have 5.25v at the Pi when idle to avoid the pi throttling due to low voltage.

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    • ?
      A Former User
      last edited by 17 Sept 2020, 18:00

      Isn't this a ideal opportunity to use the external 5v in socket on the duet-3 with a suitable external 5v psu and jumper the board accordingly to have the external 5v in supply the Rpi with a high enough current?

      Or is the external 5v there for another reason?

      And another question @dc42 as you have recommended to have an Rpi4 use it's own dedicated psu and have the duet power itself.

      What is the recommendation with regards the correct jumper combination on the duet-3 for that?

      undefined 1 Reply Last reply 17 Sept 2020, 18:02 Reply Quote 0
      • undefined
        oozeBot @A Former User
        last edited by 17 Sept 2020, 18:02

        @CaLviNx said in How big a 5v power supply needed for Duet 3 and RPI4?:

        Isn't this a ideal opportunity to use the external 5v in socket on the duet-3 with a suitable external 5v psu and jumper the board accordingly to have the external 5v in supply the Rpi with a high enough current?

        This is currently how we have our machines setup. I am also interested in if this is a recommended setup.

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        • ?
          A Former User
          last edited by 17 Sept 2020, 18:07

          @N7JTI

          here is a pic of the Rpi-4 GPIO pin out if you need it

          GPIO-Pi4.png

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          • ?
            A Former User
            last edited by 17 Sept 2020, 18:09

            if i'm not mistaken that would put a diode drop in the path of the Pi, but if you can account for that then why not; I'd still prefer to have the Pi running if the Duet is disconnected, thus custom wiring.

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            • undefined
              Luke'sLaboratory
              last edited by 17 Sept 2020, 18:41

              I use a 24V ATX supply to power my D3 + SBC setup, and wound up just directly soldering the 5v rails to the power in on the RPI and letting the duet power itself. I power USB devices from the PI, so I couldn't use the "only" 3A 5v Standby rails, which would allow me to turn off the duet w/out turning off the pi digitally.

              Luke
              http://lukeslab.online

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              • undefined
                Wally
                last edited by 17 Sept 2020, 19:43

                @CaLviNx - which connector are you using for "external 5v in socket" ?
                I'm having trouble locating this connection in the diagram here, https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Wiring_Diagram#main

                undefined 1 Reply Last reply 17 Sept 2020, 19:57 Reply Quote 0
                • undefined
                  oozeBot @Wally
                  last edited by 17 Sept 2020, 19:57

                  @Wally it's circled in red.. but you'll need to modify the jumpers right below it.

                  TF1FBCbopEsxvYAv.jpg

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                  • undefined
                    Wally
                    last edited by 17 Sept 2020, 20:02

                    @oozeBot - Thank you for the help. I'm using that currently to control a solid state relay to power on/off 120VAC input to my main power supply. So explains my confusion...

                    undefined 1 Reply Last reply 17 Sept 2020, 20:06 Reply Quote 0
                    • undefined
                      oozeBot @Wally
                      last edited by 17 Sept 2020, 20:06

                      @Wally note that this is what I asked above for clarification on if this is still a recommended setup..

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                      • undefined
                        Wally
                        last edited by 17 Sept 2020, 20:55

                        Ahh, thank you - yes this is a good question..

                        So, the big question is where else can we connect 5 VDC input to the Duet 3 if "EXT 5V" is consumed for PSON (power supply on)? In my case, applying 5 VDC here would power the solid state relay and defeat the PSON feature.

                        Currently, I power the Duet 3 via the micro USB connector (5 VDC) - is this they only work around? I'm not keen on soldering stuff to the expensive Duet 3 board.

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                        • undefined
                          oozeBot
                          last edited by oozeBot 17 Sept 2020, 20:59

                          I literally have one set up this way right now on my desk.. it appears to be the ideal setup for us. I just want @dc42 blessing after reading a few of his comments..

                          edit: and my photo is upside down.. lol

                          6A885DE6-11D5-4819-B2ED-A74C5129BC7D.jpeg

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                          • undefined
                            Wally
                            last edited by Wally 17 Sept 2020, 21:04

                            @oozeBot - thanks for the picture - literally worth a 1000 words....
                            PS: I have a very similar setup too!

                            1 Reply Last reply Reply Quote 1
                            • undefined
                              T3P3Tony administrators
                              last edited by T3P3Tony 17 Sept 2020, 21:09

                              This is the current documentation on the 5V options for the 6HC:

                              https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Hardware_Overview#Section_5V

                              Please let me know if it needs further expanding.

                              To answer the specific question of providing external 5V to the Duet and also to the RPI

                              While this is possible in theory:

                              EXT 5V -> Duet, and then Duet -> Pi over the ribbon cable

                              you then have multiple diode drops in the protection circuits
                              Edited as there is only 1 diode drop
                              its not recommended.

                              If you want to use an external 5V (suitably rated) to power both Pi and the Duet then you connect them in parallel:
                              EXT 5V -> Duet (on the EXT 5V header)
                              EXT 5V -> Pi

                              The safest way to power the Pi is through the USB C socket, the 5V pin on the SBC header bypasses some of the internal protection.

                              www.duet3d.com

                              undefined ? 2 Replies Last reply 17 Sept 2020, 21:12 Reply Quote 1
                              • undefined
                                oozeBot @T3P3Tony
                                last edited by 17 Sept 2020, 21:12

                                @T3P3Tony thank you for this clarification.. it was a concern we had that we had not been able to find a clear answer on.

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                                • ?
                                  A Former User @T3P3Tony
                                  last edited by A Former User 17 Sept 2020, 21:18

                                  @T3P3Tony said in How big a 5v power supply needed for Duet 3 and RPI4?:

                                  This is the current documentation on the 5V options for the 6HC:

                                  https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Hardware_Overview#Section_5V

                                  Please let me know if it needs further expanding.

                                  To answer the specific question of providing external 5V to the Duet and also to the RPI

                                  While this is possible in theory:

                                  EXT 5V -> Duet, and then Duet -> Pi over the ribbon cable

                                  you then have multiple diode drops in the protection circuits so its not recommended. (and probably wont work)

                                  If you want to use an external 5V (suitably rated) to power both Pi and the Duet then you connect them in parallel:
                                  EXT 5V -> Duet (on the EXT 5V header)
                                  EXT 5V -> Pi

                                  The safest way to power the Pi is through the USB C socket, the 5V pin on the SBC header bypasses some of the internal protection.

                                  @T3P3Tony

                                  This being so are the 5v lines on the SBC header pins considered dead when you only have the jumper "Int 5V EN" shorted ?

                                  Edit i have just remembered ( I will try to find the thread) that there was a thread about this very thing when the first batch of Duet-3 boards were pre-released .

                                  EXT 5V -> Duet, and then Duet -> Pi over the ribbon cable

                                  you then have multiple diode drops in the protection circuits so its not recommended. (and probably wont work)

                                  It does work i have one wired that way (and wired it that way after the it was being discussed previously)

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                                  • undefined
                                    oozeBot
                                    last edited by oozeBot 17 Sept 2020, 21:49

                                    I just measured a .33v drop at the RPi based on the way its wired in the photo I posted above. By adjusting the 5v power supply, I was able to deliver 5v to the Pi. I do understand this is bypassing the RPi's power regulator though.. so I'm torn. If this was just for myself, I think I'd trust it, but if Duet can't recommend this setup, I am afraid we'll have to rethink it..

                                    ? 1 Reply Last reply 17 Sept 2020, 21:59 Reply Quote 0
                                    • ?
                                      A Former User @oozeBot
                                      last edited by 17 Sept 2020, 21:59

                                      @oozeBot said in How big a 5v power supply needed for Duet 3 and RPI4?:

                                      I do understand this is bypassing the RPi's power regulator though..

                                      Pi doesn't regulate 5v, within lies the problem

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                                      • undefined
                                        T3P3Tony administrators
                                        last edited by 17 Sept 2020, 22:36

                                        I have edited my reply as i was working from memory and thought there was another protection diode where there is not (thanks oozebot for checking the voltage drop).

                                        There is only one diode drop and its thus possible to have 5.x volts on the 5V exp header and then have 5V on the pi header (x depends on the exact diode drop).

                                        www.duet3d.com

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                                        • undefined
                                          T3P3Tony administrators
                                          last edited by 17 Sept 2020, 22:43

                                          And regarding using the GPOI header to power the 5V on the Pi (like the Duet does). Connecting an unregulated 5V supply to those pins is not recommended (see a long discussion about it here)

                                          https://raspberrypi.stackexchange.com/questions/1617/how-do-i-supply-power-through-the-gpio

                                          In the case of the Duet powering the pi the internal 5V regulator is regulated with over current protection, however as has already been printed out a RPI4 with HDMI screen and other peripherals will be too high current for the internal regulator which it why powering the Pi from its own official supply is the safest option.

                                          www.duet3d.com

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