Can the RPi be powered by 3.3V only?

[BlueBill]

Is it possible to bypass the 5V regulator and power an RPi from a 3.3V supply via the 26pin GPIO header?

[Dilligaf]

NO

[BlueBill]

Thanks, that kills that idea.

[joan]

NO

Do you know why not?

I did an experiment feeding 3.3V from a USB dongle into the Pi's 3.3V pin. The Pi did boot and printed quite a lot out on the screen before rebooting. I wasn't sure if it was failing simply because the USB dongle couldn't supply enough juice.

[Dilligaf]

The SOC has a 5V as well as a 3.3 volt input

[BlueBill]

The BCM2835 has 5V on its pins so that might be an issue.

Anyways I'll put use an LM2675 5V & NCP1117 for 3.3V on my project. Even though I'm only using the 2675 to power the RPi.

[myrcioch]

Actually, RPi works stable even at as low level as 2.9V. You need to connect this voltage to both 5V and 3.3V rail.

[mattvenn]

I can confirm that putting 3.3 and 5v into the pi works.

[Joe Schmoe]

I can confirm that putting 3.3 and 5v into the pi works.

1) Just out of curiosity, where do you get a source of 3.3V?

2) I assume that everything works (including the serial port) - except for anything USB (e.g., the ethernet, keyboard, etc). Correct?
2a) What about the HDMI port? ISTR that that involves 5V levels...

[RoboJ1M]

Yes you can apparently.
It involves removing the 5v regulator, fooling the power pin on the bcm and voiding your warrantee, but I did read a how to do it.

I'm looking at solar power and it's one of the ways to cut down power consumption. You can even run USB peripherals if they will run of of 3.3v

I'll see if I can find the guide link.

[RoboJ1M]

http://www.daveakerman.com/?page_id=1294

It's an article on battery power.

[RoboJ1M]

Also this:

http://www.bitwizard.nl/wiki/index.php? ... spberry_Pi
However, it's probably much cheaper and easier just to buy a Model A, which (if power consumption is the issue) mostly solves all the issues

[mahjongg]

Yes, you can power the PI with 3V3 if you connect it to both the 3V3 as well as the 5V line. But do note that there might be a problem with reading out the EEPROM in the HDMI monitor, with SEC, and you cannot use any (5V powered) USB devices, unless you separate the USB 5V from the PI, and feed the USB devices directly with 5V +- 10%.

[boyoh]

This question is being answered with to many IFFs or BUTTs
The Pi was designed to to work with a regulated 5vdc in/put
The on board regulator stepped the 5v down to give you
3.3v for the GPIO in/puts & out/puts to interface with your
Projects. Back feeding the Pi causes to many problems.
The Pi was designed to learn programming and electronics.
So use the Pi within It's designed parameters

[kamilon]

The Raspberry Pi has a fairly large hacker friendly community behind it too. Being design for educating doesn't mean it isn't more than adequate for other tasks as well. Actually, everything I do with the many RPis I own is nothing close to educational.

There is a post on this forum somewhere where a guy made a weather balloon using a RPi running with only 3.3v powering it.

[mahjongg]

a guy made a weather balloon using a RPi running with only 3.3v powering it.

exactly, and its very educational to try to do something that is supposedly impossible.

[daveake]

This question is being answered with to many IFFs or BUTTs
The Pi was designed to to work with a regulated 5vdc in/put
The on board regulator stepped the 5v down to give you
3.3v for the GPIO in/puts & out/puts to interface with your
Projects. Back feeding the Pi causes to many problems.
The Pi was designed to learn programming and electronics.
So use the Pi within It's designed parameters

What it was designed for, and what it will happily do anyway, are two different things. Just connect the incoming 3.3V to the 3.3 and 5V lines (e.g. on the GPIO header) and the Pi will boot and run normally. That includes the LAN on a model B, HDMI and at least some USB devices. I do this all the time.

Dave

[daveake]

Yes you can apparently.
It involves removing the 5v regulator, fooling the power pin on the bcm and voiding your warrantee, but I did read a how to do it.

I'm looking at solar power and it's one of the ways to cut down power consumption. You can even run USB peripherals if they will run of of 3.3v

I'll see if I can find the guide link.

Although I generally do remove the 3.3V regulator, you don't have to. Doing so reduces current consumption a little, and the weight by a tiny amount, but unless these are important (which they are for me) then don't bother.

Dave