Raspberry Pi 5, DC-DC Buck down power supply from 36v, best method?

Both @Davee and @Zander, thanks guys, I read the messages here and the information provided from several sources...  I already have a multi-power system for RaspPi4's (Cluster) and yes, it is a 5Volt/15Amp supply able to source power to 5 units (3 X 5 = 15 😉 ).  I use 2 of these supplies to power 7 Rasp Pi 4's. 

"If you are building a cluster, then you will either need an official PSU per Pi, or a large single PSU. The simple calculation is # of units x 5A. You a probably get away with less if they don;t run in synch or if they are not all driving a display or making some other use of the GPU."- Ron

Getting a larger supply for the Pi 5, is possible, however, the Raspberry Pi 5 sends an identifier, and expects a response from the supply, is my guess.  Might have to dig deeper into the code, and see how that is managed.  Might have to set up a different way to get power, via the 40 pin connector like POE looks promising (With POE it looks like the ignore power requirements command works), and just avoid the USB-C altogether.  Fuses would be a must.

Again, Thanks!

Hi @fvasquez1776,

  I am pretty sure you will have seen it, but just in case, my earlier note had various links I found referring to R-Pi 5 power, some of which may be helpful.

https://forum.dronebotworkshop.com/postid/45185/

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From what I can gather, each 'bare' R-Pi 5, is likely to demand a little over 3A, perhaps up to 3.5 A, when given a 'tough' processing job, so if I were designing a supply for a cluster, I would allocate at least 3.5A, more likely 4A or more, each, to minimise the chance of any mains power dips, etc, causing the processor to crash.

(I guess if one of the processors crashes, it will be necessary to reboot the cluster, which can be more annoying.)

In addition, if there are any peripherals drawing power (USB, NVME, etc.), the total maximum drain from them should be included.

Of course, if you already have a 15A supply, you may find it is fine powering three R-Pi 5s

But my superficial relevant experience over a few decades suggests that processors with generously rated power supplies are less prone to crashing than their cousins with minimal power supplies.

Best wishes, Dave

Hi again @Davee 

I would rather receive something 2, 3 or even 4 times than not at all!!! so thanks!!!

Yea, I've starved my electronic friends before, and yes they were not so happy. 

I've even seen power supplies 'rated' at 6A, but hardly can maintain 3A.  I have a background in test, so I test things out before. 

Best,

Frank

@fvasquez1776 Both Dave and I have looked and were unable to find any doc'n specific to the Pi5 power management (schematics etc) so it will be a problem to determine how the RasPi folks are doing the 5A @ 5V. I totally forgot about POE, that may be the answer, let us know how that works out.

@fvasquez1776 (and all) I have nothing new to add to the Pi5's non standard USB-C problem except to mention that I am still interested and following this thread. I have left off with the Pi-5 using the OEM wall wart and an inverter to get MAX CPU performance for local LLM, neural networks etc running on battery power.  I have shifted my local LLM testing to an x86 platform with dedicated Nvidia CUDA GPU for the moment. In the future, if I can find a cleaner way to run a Pi5 at maximum 100% CPU performance, from a DC source, I will re-evaluate its use case in a robotic platform, as a mobile, local LLM inference compute machine.

@whitneydesignlabs Have you looked at powering the Pi5 via the POE pins? They might allow the full 5A at 5V from a normal PSU.

Waveshare has one that puts out 5V at 4.5A. Here is amazon US link.

https://amz.run/9H9M

Note this is the POE (F) model, here is Waveshare link https://www.waveshare.com/wiki/PoE_HAT_(F)

NOTE: You will need an inexpensive POE router or switch. I think I paid $50 CDN for a good switch. The POE ports have a 30W power budget (~6A) and a total budget of 65W.

@Zander, Just ordered the Pi5 PoE hat. I will give it a try. Yes, have Poe routers for Sec cams. Starting to really like Poe stuff. If this works, mega brownie points for you!!!! 🙂  Will report back here with my results.

@whitneydesignlabs I just got my first for a Pi4 I am setting up as an astro cam. It is on the balcony and I didn';t want to run power to it. With the ethernet 6+ PoE setup, I both power the Pi and have the camera connected by 2.5Gigabit to my Sony 55" TV.

I will also be making a portable version based on the Pi Zero 2 with a PoE so I can power it off something like a jackery. I know that with the Jackery I could use a Pi wall wart and USB power, but I like the one cable solution better. For outreach programs I would use a Pi Zero 2 (with WiFi) so sewveral folks can connect their tablets, phones, laptops.

@whitneydesignlabs IF it works? I think you meant WHEN it works. 😊

Hi All including Ron @zander, @fvasquez1776 , @whitneydesignlabs ,

  I just saw this as part of a mailing form Pi-Hut:

https://thepihut.com/products/pd-power-extension-board-for-raspberry-pi-5

which at first glance, appears to be an add on board, that interfaces between a 'plain' power source and the R-Pi 5 USB power in port, presumably playing the PD games and so on, to convince the R-Pi 5 that it has a 'genuine' 5V 5A source of power.

I don't need one myself, so I'll leave anyone who is interested, to read the small print and decide for themselves, whether it will meet their needs. (i.e. I am not recommending it, just suggesting it might be worth looking at, more carefully.)

Best wishes all, Dave

@davee It's confusing, on the board it seems to say 5.15V at 5A but I suspect they left out the words up to 5A for higher voltages. Since it appears to be powered by a Pi5 wall wart I don't understand what it accomplishes when they are very specific in saying ONLY one power input allowed at a time.

I won't be volunteering to buy one to check it out, I have no need and do NOT foresee ever using a Pi5 with a battery supply.

@davee and @zander, most importantly is the OR 9-24VDC...  My use is the cluster, nicer to have 1 power supply then 7 or 8.  Will also look at the efficiency of the installation.  I will most likely get 2 to check on proof of concept.  Thanks!! for all the information.

@fvasquez1776 Let us know how it goes.

Hi Ron @zander,

Re Since it appears to be powered by a Pi5 wall wart I don't understand what it accomplishes when they are very specific in saying ONLY one power input allowed at a time.

I interpreted it to mean that it could accept different 'forms' of power, but the user had to ensure only one was active.

The silkscreen print on the photo shows:

suggesting two input options:

1. (Default) USB PD 15V
2. DC (9-24V)

The first, I presume, means a USB C, PD compliant power supply, producing 15V, which is converted on the add-in board  to 5V at 3A. [15V means power input can comfortably exceed 5V 5A (~25W+losses) demand, and also (~40W + losses) for 5V 8A.]

The second, a 'simple' 9-24V power supply.

The board clearly contains its own switch mode power supply, and the silkscreen print suggests it can output up to 8A at 5V, assuming the power supply chosen can output comfortably in excess of 40W, to allow for power losses.

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If you happen to have both of these types of power supply, you are clearly warned not to connect both at the same time.

Whilst, it seems unlikely (but always possible!) someone would connect two mains-powered supplies at the same time, I suspect this maybe intended as a warning to anyone considering trying to use this with a mains powered (USB PD) supply, at the same time as a battery supplying 9V-24V, as a back-up arrangement. (i.e. DON'T DO IT!)

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However, I do not have the board, nor have I carefully read the available documentation, so anyone contemplating buying or using one of these boards should carefully check with the official documentation, etc., before taking any actions.

Best wishes, Dave

@davee I just realized that the Pi Logo'd USB-C cable I saw in a photo, is the output of the board that connects to the Pi5. Nothing to see here, now back to our regularly scheduled program.