Powering the Pi from GPIO


15 posts
by Alfadaz » Sat Nov 03, 2012 6:47 am
Reading the fax, i believe i can power my Pi using the GPIO.

What are the issues with powering the Pi with this method? (I have already bypassed the polyfuses)

I also notice there are 2 x 5v pins on the GPIO (2 and 4), does it matter which one is used?

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by joan » Sat Nov 03, 2012 10:05 am
I use P1-2 as I think P1-4 was orignally marked as do not connect.

Some say you should have a fuse to protect the Pi. I can't be bothered.
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by Narf03 » Sat Nov 03, 2012 11:17 am
There was a version of pi schematics saying pin 2 and pin4 are both connected, 5v, i think it has been changed to pin 2 only.
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by Cloudcentric » Sat Nov 03, 2012 12:07 pm
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by jojopi » Sat Nov 03, 2012 12:08 pm
All production Pi s have 5V on P1-2 and P1-4. But there have been conflicting statements on whether we should expect P1-4 to change in the future.

You need an external fuse if you are using a high-power source like an ATX or bench supply without current limiting. With a 2A supply it is not important.
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by Joe Schmoe » Sat Nov 03, 2012 12:45 pm
jojopi wrote:All production Pi s have 5V on P1-2 and P1-4. But there have been conflicting statements on whether we should expect P1-4 to change in the future.

You need an external fuse if you are using a high-power source like an ATX or bench supply without current limiting. With a 2A supply it is not important.


But only if something bad happens.

Such as ?????
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by joan » Sat Nov 03, 2012 1:01 pm
Shorting out ground to power on the board or plugging a shorting device into the usb? Both might burn out the ground or power rails on the Pi. Only reason I can think of for a fuse.
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by Joe Schmoe » Sat Nov 03, 2012 1:05 pm
joan wrote:Shorting out ground to power on the board or plugging a shorting device into the usb? Both might burn out the ground or power rails on the Pi. Only reason I can think of for a fuse.


OK. So the idea is that a fuse might protect the Pi from catching fire and burning your house down. Sounds like the Pi itself might still end up as toast, but at least your house is intact...
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by techpaul » Sat Nov 03, 2012 2:01 pm
joan wrote:Shorting out ground to power on the board or plugging a shorting device into the usb? Both might burn out the ground or power rails on the Pi. Only reason I can think of for a fuse.

If you have a short on your Pi, it will still have a problem even with a fuse that amy not blow/open quick enough. If short on Pi, then Pi is already dead. A power supply can do overcurrent protection quicker than a fuse.

If you have a shorting device on your usb or whatever it will probably blow other things as well, any decent hub should limit the power to each port, but then again getting decent not cheapest hubs these days is rare :P
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by techpaul » Sat Nov 03, 2012 2:06 pm
jojopi wrote:All production Pi s have 5V on P1-2 and P1-4. But there have been conflicting statements on whether we should expect P1-4 to change in the future.

Check Wiki and other news articles that state pin 4 will be +5V and the other GND pins will remain.
You need an external fuse if you are using a high-power source like an ATX or bench supply without current limiting. With a 2A supply it is not important.

Size of the current source is not really the issue, as the Pi or anything else will try to draw whatever current it requires, if you have a short something is already dead. Even large PSUs have overcurrent protection, and for really large currents the wires and connectors will act as a fuse.

You can puit a fuse if you want, you can also put lightning conductors if you wish, work out what is most likely method and place of problems you can protect against.

Overvoltage is your biggest concern.
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by jojopi » Sat Nov 03, 2012 2:38 pm
techpaul wrote:Check Wiki and other news articles that state pin 4 will be +5V and the other GND pins will remain.
Ah yes, Eben has withdrawn the conflicting statement from last week: http://www.raspberrypi.org/archives/2233
techpaul wrote:Even large PSUs have overcurrent protection, and for really large currents the wires and connectors will act as a fuse.
The wires will act as the kind of the fuse that disconnects power from an electrical fault, or the kind of fuse that communicates fire? If you connect a 250W supply to a 3.5W board without sensible protection you very likely invalidate your insurance against the consequences.
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by pluggy » Sat Nov 03, 2012 2:43 pm
Cloudcentric wrote:http://elinux.org/RPi_Low-level_peripherals


Hmmm, the picture on there has changed since the last time I looked. P1-4 used be marked as No Connection, which may have been a few months back. My hand crafted GPIO power header I built at the time uses P1-2 & P1-6 for 5V & GND
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by techpaul » Sat Nov 03, 2012 7:11 pm
techpaul wrote:Even large PSUs have overcurrent protection, and for really large currents the wires and connectors will act as a fuse.
The wires will act as the kind of the fuse that disconnects power from an electrical fault, or the kind of fuse that communicates fire? If you connect a 250W supply to a 3.5W board without sensible protection you very likely invalidate your insurance against the consequences.[/quote]
Most 250W supplies will not turn on without a minimal load way above 3.5W

Most precautions people think they need in here are way over the top.
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by Alfadaz » Mon Nov 05, 2012 10:30 am
Many Thanks guys :)

I have seen a lot of people are now suggesting 5.25v power supplies which i presume to get around the low voltage readings between TP1 and TP2.

What is the max voltage that the Pi can take? While scrummaging around i found a 5.6v 2.5A power supply, but i think that might be a little to high.

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by joan » Mon Nov 05, 2012 11:03 am
I used to power my Pi via a 5V wall wart phone charger. From memory TP1/TP2 showed 5.7V plus. I didn't have a problem. I don't know what damage it could do to the Pi. Perhaps the 3.3V regulator has to work harder and gets warmer, perhaps the concern is for things on the USB bus.

Mind you, given that my 5V supply was bunging out 5.7V plus I wonder what your 5.6V supply is producing?
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