danieljay
Posts: 49
Joined: Sun Sep 16, 2012 5:01 pm
Contact: Website

Current draw from Raspberry Pi

Fri Apr 19, 2013 3:18 am

Greetings all!

I have a quick question about current draw from the raspberry pi with input peripherals/hardware through GPIO pins;


So thumbing through the basic documentation, I found this bit of information:

Power pins
The maximum permitted current draw from the 3.3 V pins is 50 mA.
Maximum permitted current draw from the 5 V pin is the USB input current (usually 1 A) minus any current draw from the rest of the board.[14]
Model A: 1000 mA - 500 mA -> max current draw: 500 mA
Model B: 1000 mA - 700 mA -> max current draw: 300 mA
Be very careful with the 5 V pins P1-02 and P1-04, because if you short 5 V to any other P1 pin you may permanently damage your RasPi. Before probing P1, it's a good idea to strip short pieces of insulation off a wire and push them over the 5 V pins so you don't accidentally short them with a probe.


so, this leads me to my question; I have a 300mA rated fan motor through the 5v, a usb dongle rated at 100mA along with a webcam via USB thats drawing 700mA. If I use a larger power supply (current one is rated at 3.1 Amps), will this be enough current for the Pi? does the Pi only draw a max current of an Amp?

klricks
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Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: Current draw from Raspberry Pi

Fri Apr 19, 2013 3:50 am

If you power though the micro USB input then the main fuse F3 will limit the current to about 750mA or so. If the total current draw is higher than 750mA the RPi and/or peripherals attached will not run reliably.
If you attempt to draw more than 1A through the RPi then the fuse will trip after a few seconds.

You could use your 3A power supply to run the RPi and other things such as your fan, HUB, Drive etc... by using a terminal block or some kind of 'Y' cable to tap off power before the RPi.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

danieljay
Posts: 49
Joined: Sun Sep 16, 2012 5:01 pm
Contact: Website

Re: Current draw from Raspberry Pi

Fri Apr 19, 2013 4:22 am

understood;

so to clarify; a setup using a USB Y cable that originates at main power source, then feeds one end to the main board, then the other end powering an external USB hub (to power usb peripherals) could be a reliable setup?

danieljay
Posts: 49
Joined: Sun Sep 16, 2012 5:01 pm
Contact: Website

Re: Current draw from Raspberry Pi

Fri Apr 19, 2013 4:27 am

to clarify also, this is a usb power supply. I understand though what you mean with using a separate power source (since the more items you add, the more current). I want my setup to solely use a single power supply.

klricks
Posts: 6789
Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: Current draw from Raspberry Pi

Fri Apr 19, 2013 12:49 pm

danieljay wrote:understood;

so to clarify; a setup using a USB Y cable that originates at main power source, then feeds one end to the main board, then the other end powering an external USB hub (to power usb peripherals) could be a reliable setup?
Yes as long as the total current draw is <= the power supply rating and the wires in the cable are large enough gauge (diameter) to handle the current.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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