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I'm trying to decide what is the best option for powering a Pi4. The specs mention for a minimum of 3A. Let's consider we would also like to connect a 2.5" drive to the Pi4. Could someone more experienced with power supplies help me with the following?

  • How far can we go with a good 2.4A USB charger?

  • The official power supply is rated 5.1V/3A. Does this mean that this may turn out to be inadequate?

  • Some 3rd party chargers (e.g. the one discussed here) are rated for 3A in Quick Charge mode. Will the QC mode be activated with RPi4? Or the charger will operate as a regular 2.4A charger?

  • How can we tell apart 3rd party chargers that would work with RPi4? Are there any of them? I've seen a couple of models mentioning 5V/4.4A output. But I'm afraid this is only the aggregate amperage (they were multi-port USB chargers).

  • Well, a 2.5" drive might take 500mA or more. So I think the official 5.1V 3A PSU does not cater for your special needs. These couple of years I have been using 220VAC to 12V DC 5A/10A PSU (Well, those cheapies you can find at eBay or AliExpress). Then I step down 12V (or 11.1V if I am using LiPo power banks) to 5V 3A/5A/10A for my different projects. In case you ask, I NEVER use any of those ugly looking plastic covered wall wart dumb or smart "chargers" for my Arduinos or Rpis! – tlfong01 Jun 26 at 14:30
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The best option is a good quality power supply, as cheap brands may say they are rated at 2.4 amps, when they don't actually supply that much. Based on the numerous bad experiences i've had with 3rd party chargers, i'd highly recommend buying the official one from the foundation!

Whether that is adequate for the hard drive is another question. I haven't tried the Pi 4 yet, but my 3B actually worked fine (with no low-voltage warning) with a 1A USB hard drive plugged into it. The adapter powering the Pi was rated at 2.1A.

  • 1
    Apparently the USB-C port on the Pi 4 is non-spec and many quality "e-marked" chargers will detect the port is wired incorrectly and refuse to charge. Looks like a fix is in the offing though. Source: arstechnica.com/gadgets/2019/07/…: – F1Linux Jul 9 at 16:17
  • All answers made meaningful contributions. Because of the non-compliant USB-C implementation, I've accepted this as the right answer. Until a new version of the board comes out, probably the safest bet is to go with the RPi foundation PSU. – m000 Jul 10 at 17:23
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The spec specifically states that:

A good quality 2.5A power supply can be used if downstream USB peripherals consume less than 500mA in total.

Using a 2.4A power supply with the Pi 4 and a 2.5" HDD is going to be borderline assuming a typical power rating of the 2.5" drive of about 1.8W to 2.7W (see here). From the above statement - after all it really says that the Pi will need just 2A - the official supply should however work.

According to this answer Quickcharge modes are likely not going to help.

5

Use a PoE Hat:

Third-party USB-C charging devices can be cheaply wired, potentially destroying connected devices as well as starting fires. A safer alternative is to power your Pi using PoE which beyond reducing these risks, offer additional benefits:

Benefits:

Using a PoE Hat is easy to setup and enables you to:

Additional Requirements:

In addition to a PoE Hat, you'll require a PoE switch and some decent Ethernet cables. Some suggestions for which I've had great results with my own PoE Hat use are:

Cost Comparison: Mains vs PoE: Total cost of a PoE Hat + 5 ft Tripp Cat6 24 AWG Ethernet cable = £20, versus £8/each for a "official" (genuine; not third-party) Raspberry Pi USB-C mains power supply unit. But for the £12 difference the additional benefits described above I feel are worth the small premium.

Pi 4 Compatibility: Haven't myself yet been able to get a Pi 4 (vendors I tried were out of stock unsurprisingly) but found this link to a Register article about the Pi 4 which notes the PoE Hat IS compatible in their report on the new Pi

  • I bet one can also start a fire with a crappy PoE hat. If anything, 48V has higher damage potential than 5V. – Dmitry Grigoryev Jun 28 at 23:23
  • @DmitryGrigoryev I supplied links to quality Ethernet cables as well as a reputable Vendor & model of a PoE switch. Indeed, I’ve used this combination to power 8 Pi security cameras for over a year now without issue and I sleep like a baby. I also provided links to articles describing blown up gear and fired from cheap third party usb-c cabling. “Crappy” PoE? PoE is widely used in industry and proven. – F1Linux Jun 28 at 23:37
  • I don't think you understood me. I didn't say all PoE equipment is bad, but some of it certainly is. The same is also true for USB. You make it sound like USB-C is somehow unsafe, and link to an article I don't find trustworthy as proof. Do you seriously think that the fact that you "sleep like a baby" while using PoE is a valid technical argument? Sure, I readily believe you that your $100 PoE switch is better quality than a $5 USB brick. – Dmitry Grigoryev Jun 29 at 13:40
  • Please read the links proved in my answer. There is a much larger chance of buying “crap” third-party usb-c power supplies on Amazon that can cause a fire or destroy connected equipment then there is using my proposed solution-which I’ve been using for about a year now. I feel it’s proven. As for lack of empirical support, I gave links why the usb-c stuff could be iffy. Your response asserting the POE Hat was “crap” and implying it was a greater fire hazard was put opinion without anything to support your view – F1Linux Jun 29 at 16:35
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How can we tell apart 3rd party chargers that would work with RPi4?

You can either rely on reviews or ask the seller and take their word for it, or you can get the supply, test it, and return it back if it doesn't perform. Obviously, in the latter case you'll want to buy it from a place where you can return it for free.

There is no way to tell from the labels how much current a power supply can really deliver. I've seen 2.5 A chargers which go down to 4V at nominal current. Good enough to charge a phone, not nearly good enough for a voltage-sensitive device such as an RPi.

One place which (surprisingly) sells very decent cheap 5V PSUs is IKEA. They offer a 3-port charger with 3.4A total current, 2.4A per port, which really holds its promises. If you need lots of power, plugging the RPi in one port and a powered hub in another gives you a combined power of 17W.

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