7 Replies Latest reply on Mar 24, 2020 1:13 PM by shabaz

    Pi Desktop: max current output?

    rootard

      Hello

       

      I have purchased a Element14 Pi Desktop that I'm using with my Pi 3B+ and the original Raspberry 2.5A PSU.


      So far it was running fine with the RTC hat + SSD + 2 fans on the GPIO (1 for the heatsink and one for the case) + an Aeotec ZWave key connected on the USB port.

      However the Pi froze after a few hours when I added an USB RFXCom device.

      I suspect a power issue. I've tried to used a bigger 3A PSU with same results.

       

      What is the maximum current provided by the Pi Desktop Hat?

      Is there a fuse limiting the power provided to the Pi board?

      Is there a way to solder the fans directly to the Hat input in order to avoid voltage drop? If yes on which pins?

       

      Thanks

        • Re: Pi Desktop: max current output?
          colporteur

          My limited understanding the Pi3B+ can only source the 2.5amps. Changes in the Pi4 only supported higher current capabilities. Even if you had a 3amp PS on the pi3's it was not used. I expect a 3amp PS would have less of a chance of sagging if under load but the Pi itself couldn't draw the current.

           

          Now I don't have the technical reference to provide. This is anecdotal from what I have accumulated.

          • Re: Pi Desktop: max current output?
            shabaz

            A Pi 3 doesn't need two fans. It's even possible to use fully passive heatsinking with the Pi 3 under full load, but that's difficult with that enclosure.

            The fans will be consuming most power, not the RFXCom device or your other wireless device. If you can remove one fan, then there's a fair chance you may be ok in terms of power consumption, and it will still run at full speed.

            • Re: Pi Desktop: max current output?
              rootard

              shabaz thank you for your reply. Unfortunately this Element14 case is very tight and suffers from poor ventilation so a passive heatsink is not enough.

              This Pi is critical as it runs all my home's domotics 24/7 incl heating, roller shutters and light.

              I had to dig holes in the case and added 2 fans, one on the case side and one on the CPU heatsink to have the cpu temperature drop down to 55°C.
              As I have a 3A PSU I'm going to investigate connecting the fans directly to the PSU, not to the Pi.

                • Re: Pi Desktop: max current output?
                  colporteur

                  It is easy to suggest after the fact there are alternate solutions to cooling. I am impressed with the adafruit solution https://www.adafruit.com/product/4557 . Expensive is scaling and infrastructure intensive but it resolves airflow issues.

                  • Re: Pi Desktop: max current output?
                    shabaz

                    That's a good option, to connect directly to the PSU.

                    As a datapoint, I'm running a Pi 4 with no fan, in an enclosure with vents, and it runs very warm, but it's been stable for weeks in a room at 23 degrees ambient.

                    Pi 3's are easier to manage with some vents (could cut them in the enclosure) and a small heatsink, although if you expect to use all four cores, then it's more difficult (It can be solved with a larger heatsink and heat pipe for a fully passive solution, or with a single small fan + heatsink).

                    I've one Pi 3 in a capacitive touch display enclosure, relying solely on some vents, and several others just run with a heatsink. I don't believe they have throttled, but I expect them to do so if all four cores are used. My workloads don't usually involve that, your might be different.