# max number of Pi 3's to safely plug into a wall [duplicate]

This post is basically a repeat of: Is there a maximum number of Pis that I can power from the same wall socket?

However my situation is slightly modified. Particularly for wall sockets in Denmark, which based on this link: https://www.worldstandards.eu/electricity/plugs-and-sockets/, the standard is 220-240 V, and 16 A.

I need to plug at least 60 raspberry pi's within close proximity of each other (for science :) ), and i want to make sure i am doing this correctly..

based on this guide: http://raspi.tv/2017/how-much-power-does-pi-zero-w-use, a Pi 3 is using 350mA max, which is what i used for the calculation made in the referenced stackexchange link

my calculation is as follows:
1) `240*16=3840 watts from wall`
2) `.35*2.5=.875 watts one Pi 3 uses`
3) `3840*.=3264 watts from wall based on 85% efficiency`
4) `3264/.875=3730 Pi 3's that in theory could be plugged into the same wall circuit`

apologies for the repeated post, but can someone please confirm my calculation that with a 2,5 amp power supply and 85% efficiency, i can in theory plug ~3730 Pi's into a socket (or a number in that range)?

essentially i want to guarantee that 60 Pi 3's will be safe to plug into the same socket. help is greatly appreciated..

• Since you'll need 5v to power the boards wouldn't it make more sense to buy a single 5v PSU in the 1000w range and plug that into the wall (and know its a 1000w load) then the Pis into that? I think you'll find a Pi3 uses considerably more than 350ma @ 5v with things plugged in and doing useful work. raspberrypi.org/help/faqs/#powerReqs. 60 wall adapters is pretty inefficient. Feb 21, 2018 at 13:06
• The only step that is questionable is step 2 in your calculation: .35*2.5 . What do this figures mean? .35A * 2.5V? That would not be enough (voltage). I would calculate 5V * .75A at least. Feb 21, 2018 at 13:56
• What power supply units (psu) do you want to use? Your calculation is missing the current drain of these 60 psu (cue capacitors). If you connect them all at same time with one flip switch, it might get interesting. Do you want to operate 60 raspberry pi's at home or at university/laboratory/similar? I hope you have a fire extinguisher catchable (just in case). Feb 21, 2018 at 14:30
• "This post is basically a repeat of: Is there a maximum number of Pis that I can power from the same wall socket?" -> Yes. "However my situation is slightly modified." -> Not substantially it isn't. Feb 21, 2018 at 15:08

The ultimate arbiter here is power.

a Pi 3 is using 350mA max

No, a Pi 3 is using 2500 mA max, but it also design to provide power to peripherals through USB, to a reasonable extent, without browning out. So let's assume without peripherals attached, it won't use more than 2A (as it turns out, this figure is not a problem anyway).

You could confirm this by using an ammeter in line with one and running some appropriate tests.

Anyway, 2A @ 5V = 10 watts of power.

A 16A 220V circuit should provide 15 * 220 = 3520 watts of power. This is probably fairly realistic, as it is not impossible to plug several 1500 watt heaters, etc. into a household circuit.

There will be some power loss in converting down to 5V DC. Again, to be safe, let's go with half that, 1720 watts. Since you only need 60 * 10 = 600 watts, this should be plenty.

A more pessimistic figure might assign the full 2.5 A to every Pi, meaning they need 13 watts, and divide the wattage of the circuit by 4 (that's pretty pessimistic), in which case it can still provide 880 watts. The 60 Pis still scrape by at 780 watts.