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I'm making a NAS with a Pi 4B, powered by a Meanwell RS-25 (5v 5a) psu. However, as far as I know, the Pi can only be powered via USB C, but the problem is all my breakout boards are limited to 500ma. The Pi needs to be able to draw at least 3 amps since a hard drive will be directly connected to it.

Are there any workarounds I can use or am I stuck with a generic USB brick?

user485
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3 Answers3

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"However, as far as I know, the Pi can only be powered via USB C" "The Pi needs to be able to draw at least 3 amps" - I wonder where people get these alternate facts or why they choose to believe them rather than the official documentation.

It is certainly possible; I run most of my Pi from a single supply.

That is not to say there are not issues; first adequate power supply, adequate cabling, reliable connections, availability of suitable connectors etc. and the ability to construct the cabling, but it is possible.

No matter the power source, getting the Pi to power external HDD is challenging (the performance of the Pi USB power is underwhelming), and it best done with a powered drive or hub (and in this case finding a suitable hub is itself a challenge).

See Raspberry Pi Power Limitations

Milliways
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  • "The USB hub on the B models does not appear to be compliant to the USB specification and does not limit current. Individual ports can supply in excess of 500 mA independent of negotiation, subject to the overall maximum limit and adequate power supply." The drive itself along with the adapter uses ~800 ma total, so I'm guessing I'd be fine – user485 Jul 18 '21 at 06:32
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You are stuck with a brick if you want a realilable system. You state you are planning on building a NAS (Network Area Server) all the drive(s) also need power, how are you going to supply that? Look at using an external powered hub (brick) that can supply the necessary power, it also offers protection to the Pi. You did not state where 500mA limit comes from so I cannot evaluate that part. Each device will draw what it needs until power is no longer available typically because the power supply is undersized as it appears you will be. You have a good power supply but it has ratings for a reason. You might want to check the Pi and its current limit protection, it can only pass so much, that varies by model. If it is a fuse as most are you really do not want to push it to that limit.

Gil
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  • It doesn't seem you read the comment I left the other guy. I'm using one drive that draws no more than 800ma, adapter and all. Since then I've found out that according to the official documentation, the USB ports are capped at a total of 1.2 amps. If the only limiting factor is my power supply, I think I'll be fine. – user485 Jul 20 '21 at 17:00
  • I did, and at this point I do not believe it will be reliable. You stated: "all my breakout boards are limited to 500ma", is that for 1 or 10 boards?? What are the breakout boards as that will have a bearing on the power supply. Show each of your loads including your safety factor for each. What is the startup surge on the HDD? – Gil Jul 20 '21 at 18:58
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I would use these 5A from your PSU and use 2 connectors: 1 to Pi and 1 to the NAS. Directly from PSU to NAS. Otherwise you will spend a lot of time trying to find why the NAS/Pi have issues.

Zygfryd Homonto
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