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Although I did some research I will still ask, maybe somebody come up with something new.

I have 9 node Rpi4B+ cluster Under load I have noticed that some nodes start getting Under-voltage errors. At the moment I'm powering them all from single USB hub I-TEC USB 3.0 Charging HUB 16port + Power Adapter 90 W which I hoped would be up to the task.

From what I understand the botched USB-C on rpi4 does not limit charging, just prevent it altogether if the charging cable have chip. ( mine does not )

There are also two flash drives in each node ( USB 3.0 )

What can I do ? Using PoE ... but all PoE hats I have seen supply just max 2.5A and rpi4 needs around 3A ( right ? ) Also since I have 9 nodes... well I can't find decent PoE switch that would not cost 250Eur+

Other option, get some random 12V power supply + 12V to 5V power convertor/bucks and wire it that way ( kind of messy solution )

What else is there ?

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90W / 9 devices is 10W per device. That's about enough for a Pi 4 alone, but those 18 USB sticks will also need some power, perhaps another 20W-30W. And you'll want to have some extra power reserved for peak consumption, losses in the cables and the hub, etc.

Additionally, looking at similar hubs on my local Amazon, I see the following line in the description:

Each USB port is capable of delivering up to 1.1A of current.

Get an industrial 5V power supply: it will be cheaper than a hub and 40A supplies are available. Make sure your wiring can support large currents.

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I use a repurposed PSU from a defunct desktop PC, easy to do and with plenty of 'grunt' for your cluster. Loads of guides online on how to do it and best of all very cheap if you dismantle a scrap PC.

  • Plenty of old PC psu around my home, I might do that. Thanks – VladoPortos Nov 10 '20 at 10:30
  • Be mindful of the hiccup mode some PC supplies implement. You may need to attach dummy loads to the outputs you don't use. – Dmitry Grigoryev Nov 11 '20 at 15:13
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The industrial solution to this is to use a blade, such as a Bitscope Blade

  • I have seen these but its just for 4xPi and its flat, while I would prefer horizontal to fit more nodes... I might end up doing my own back plane, to be honest its not that difficult, I was thinking the same as Bitscope where I would attach "shield" to pi, power it through pins and it would extend with connector like PCIe that would plug into back plane... I just did not wanted invest that much time to it and hoped for easier solution, than waiting months for components, pcb etc... :) – VladoPortos Nov 12 '20 at 14:20
  • Bitscope do do a box which will hold ten of these blades, but that’s not quite enough for the initial customer, Los Alamos Lab in USA. They wanted around a thousand plus Pi to simulate high performance cluster architectures. – Nick Nov 12 '20 at 19:57

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