docteur.blanchard
Posts: 23
Joined: Wed Sep 19, 2012 4:52 pm

Wich Power Supply for several RPI

Wed Nov 07, 2012 10:27 pm

Hello,

I have an important project where 36 RPI need to be connected on the same power supply 220/5v.

I wish to know the number of amp on 5v to give enough of power to all of RPI.

Thanks for your help

thsBavR10
Posts: 233
Joined: Sat Jul 21, 2012 3:11 pm

Re: Wich Power Supply for several RPI

Wed Nov 07, 2012 11:32 pm

- simple and safe attempt: 1A per Pi results in 36 A
- lowest power comsumption, no interfaces, no overclocking 0.5A per Pi -> 18A
- the average: 0.75 A per Pi, gives a total of 27A
what about 30A @ 5V ?

docteur.blanchard
Posts: 23
Joined: Wed Sep 19, 2012 4:52 pm

Re: Wich Power Supply for several RPI

Wed Nov 07, 2012 11:50 pm

Thanks for your reply.

Do you think that if i use a computer power supply of 300 watts and that i modify the connector to get only the 5v, it should be enough?

Where can i have the usb connection schema to find the + and the - on the usb ?

Thanks again
Best Regards
Marc

docteur.blanchard
Posts: 23
Joined: Wed Sep 19, 2012 4:52 pm

Re: Wich Power Supply for several RPI

Wed Nov 07, 2012 11:58 pm

Sorry, i just find it.

I post the schema for whom that this topic interests.

When we cut the usb cable, usually the + is the red and the - is the black.
These cables are more bigger that the 2 others (pin2 & 3)

1 is +5V.
4 is Ground, 0V.

Here is the schema:
Image

Best Regards

SirLagz
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Re: Wich Power Supply for several RPI

Thu Nov 08, 2012 12:46 am

docteur.blanchard wrote:Thanks for your reply.

Do you think that if i use a computer power supply of 300 watts and that i modify the connector to get only the 5v, it should be enough?

Where can i have the usb connection schema to find the + and the - on the usb ?

Thanks again
Best Regards
Marc
Check the ratings on the PSU sticker and see if it can supply 30A on the 5v rail.
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thsBavR10
Posts: 233
Joined: Sat Jul 21, 2012 3:11 pm

Re: Wich Power Supply for several RPI

Thu Nov 08, 2012 6:22 am

docteur.blanchard wrote: Do you think that if i use a computer power supply of 300 watts and that i modify the connector to get only the 5v, it should be enough?
from http://en.wikipedia.org/wiki/PC_Power_Supplies -> Power rating: ..
A 3.3 V rail may have a 10 A rating by itself (33 W), and the 5 V rail may have a 20 A rating (100 W) by itself, but the two together may only be able to output 110 W
That wouldn't be enough.
You have to check this for your special power supply or data sheets from manufactorers. (http://en.wikipedia.org/wiki/List_of_PC ... .28PSUs.29)
For connecting the Pis to the supply it could be better to build / look for an "dispatcher" and use standard usb cables.
Have a look at http://www.usb.org / http://en.wikipedia.org/wiki/USB

pinoccio
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Re: Wich Power Supply for several RPI

Thu Nov 08, 2012 3:24 pm

Just a hint:
I had problems when powering from a computer ATX PSU, due to voltage drop on the cable and especially on the USB hub. The provided voltage was about 5.1V on the source, but only <4.6V on the device! So you better use custom solid cables, not a standard cheap USB-2-microUSB cable. And don't use a powered HUB as a power splitter (or use a verified one, which is capable of transferring such currents). ;)

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RaTTuS
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Re: Wich Power Supply for several RPI

Thu Nov 08, 2012 3:29 pm

as most computer plugs are going to be 13Amp max your not going to be able to supply enough power from one for 36 RPi's ....
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itimpi
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Re: Wich Power Supply for several RPI

Thu Nov 08, 2012 3:39 pm

RaTTuS wrote:as most computer plugs are going to be 13Amp max your not going to be able to supply enough power from one for 36 RPi's ....
Not true as the socket is at 240V AC! A better way to think of that is that is about 3000Watts, and a Pi consumes something like 3 Watts. Therefore the limit is more like 1000 Pi's from 1 13 Amp socket. It makes you think when you consider it that way.

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RaTTuS
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Re: Wich Power Supply for several RPI

Thu Nov 08, 2012 4:10 pm

yeah that makes more sense
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