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I'm not an electrical engineer so apologies for the rather basic question. I've found myself with multiple pi's and felt it was about time to look for some other power solutions other than powering each one with its own adaptor.

From what I understand the pi 3 model b needs 5V and 2.5A. Now I don't know how to read the specifications on USB chargers so I found this one PowerPort+ by Anker which says output 5V and 2.4A per port.

I also found some other ones which says 2.4A per port or 4.4A max. I don't understand what the max means. Does it mean you can connect one device to 2 or more ports to give it a higher current (A)?

Would any of these work?

Also, what would happen if the port has more than 2.5A?

I'm also trying to avoid using the GPIO ports because the pi site says that the protection is in the USB port.

  • Raspberry Pi Power Limitations – Milliways Feb 1 '18 at 2:44
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    "I don't understand what the max means. Does it mean you can connect one device to 2 or more ports to give it a higher current" Current is drawn from a supply. The max rating of the supply is the most current that can be drawn from it. If something draws less than that, then there is less current flowing. If nothing is being drawn, then there is 0 current. – goldilocks Feb 1 '18 at 15:14
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For your first question about amperage, here's a layman's attempt at an answer:

In this case, the 2.5A rating of the Pi is a measure of the maximum amount of electricity it wants made available to it from the power supply. Each individual Pi you plug into a port on the Anker should be fine because it has a rating of 2.4 Amps-per-port, which is "close enough".

Now on to the second question: What is the "second" rating (in your case "4.4A") about?

It's the total amount of electricity the entire device is capable of giving out all at the same time. So a 4-port, 2.4A power supply could potentially be called upon to give out 9.6A if all four ports are drawing their maximum simultaneously. But, if it's rated only at 4.4A, then you won't be able to plug in multiple Pis simultaneously because they will be starved of electricity. However you could plug in a few phones to charge them at a slow pace, etc.

Now to answer the BIG question: Will it work?

How do we know then if the power supply you chose will support all four ports at 2.4A simultaneously? We need to know it's power rating. In this case, the specs say it is a "60 Watt" supply. All USB ports are 5 volt devices, so now for a little basic math:

Watts = Amps X Volts

This means that in the case of the Anker:

Amps = 4 ports x 2.4 amps-per-port = 9.6
Volts = 5
Watts (required for all four ports) = 5V * 9.6A = 48W

So, we would only need 48 Watts to supply all four ports with 2.4 Amps simultaneously. The Anker is capable of 60 Watts, so it has power to spare.

RESULT: You should be just fine with this power supply.

Good luck, and have a fun time with your Pis!!!

  • Thank you so much. That is such a good explanation! I haven't found one like that anywhere :) – nbz Feb 2 '18 at 1:22
  • Glad it helped! Have fun with all those Pis! :) – MrChips Feb 2 '18 at 19:09
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Look into the Specs section:

PowerIQ Output: 5V=6A(2.4A Max Per Port)

USB PD Output: 5V=3A/9V=3A,15V=2A/20V=1.5A

Strictly speaking, you can power two Raspberries from USB-A ports (marked IQ), and another one from the USB-C port (marked USB PD). This includes any external USB devices you attach to them. Since it's quite unlikely that all Raspberries will need a maximum current exactly at the same time, you could even power 3 Raspberries from USB-A ports with very little risk.

Powering an RPi from every port will work if you don't plug high-power external devices like HDDs/SSD into every Pi (they'll still get an average of 6/4 = 1.5A, which is more than an average 1A needed by the Raspberry itself). If you attach an HDD to every Pi, there will be a risk of under-voltage if e.g. all disks decide to start at the same time: the disks will consume roughly 1A each, and the Raspberries will be left with 6-4=2A, which is only 0.5A per board, clearly not enough.

Note that 60W is the input power rating, not the output power rating, so it's rather irrelevant. That is, if you get a power supply with the same output current ratings at 5V but labelled 90W, you won't be able to power more Raspberries with it.

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