alexellis
Posts: 53
Joined: Tue Nov 26, 2013 10:00 am
Location: United Kingdom
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Re: Running Raspberry on 3.3 V

Wed Dec 04, 2013 2:59 pm

I'd like to try running my PI from AA or AAA batteries using a regulator but I don't want to desolder the existing LDO. It sounds like you are saying this is possible.

Can you recommend component codes for the 3.3 regulator? Then the regulator is connected to the battery holder and +3.3 and +5v + ground on the GPIO pins?

Thanks,

Alex
karlkiste wrote:
daveake wrote:The risk of damaging the Pi is minimal and you certainly don't want to risk losing your payload because the batteries died before you got to it.
The batteries should not be affected. If 5V and 3.3V rails are wired to 3.3V both, the LDO shouldn't consume more than a few milliamperes (max. 10 mA says the datasheet). Those can be saved by just cutting both the little wires on the LDO. Desoldering then has only impact on the weight, not on the current draw. The weight is not very high - I would estimate that shaving the GPIO pins will have a bigger effect.

But, I agree, with a good, powerful, regulated soldering iron with a short, wide, hot tip, desoldering shouldn't be a problem. Components tend to die when soldered for too long, not too hot. And, the LDO is broken anyway. It's the surrounding components that count.

Eng. Hazem Habbab
Posts: 1
Joined: Sun Dec 08, 2013 10:09 pm

Re: Running Raspberry on 3.3 V

Sun Dec 08, 2013 10:20 pm

Hello dear, why dont you use a step up Dc-DC converter to rais the 3.3V to 5V anf then u can feed it to your Raspberry PI easily?

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FiddlerJones
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Location: Italy

Re: Running Raspberry on 3.3 V

Mon Dec 09, 2013 1:15 am

alexellis wrote:I'd like to try running my PI from AA or AAA batteries using a regulator but I don't want to desolder the existing LDO. It sounds like you are saying this is possible.

Can you recommend component codes for the 3.3 regulator? Then the regulator is connected to the battery holder and +3.3 and +5v + ground on the GPIO pins?

Thanks,

Alex
If by "component codes" you mean "recommended components", I'm using this: http://uk.farnell.com/tracopower/tsr-1- ... dp/1696319 and it works perfectly. It's light, cheap and very efficient (~85%)
But any switching regulator with the input range you're looking for, 3.3V output, and enough power (~1A/3.3W) is going to do the trick.
If you meant "software codes in order to use the regulator / the RPi with 3.3V", there's no need to do anything like that.

The connection is simple:
1) First, connect the negative terminal from the batteries to the regulator and to the RPi GND
2) Combine the 3.3V and 5V lines and connect them to the regulator output
3) Connect the batteries positive terminal to the regulator input

You can leave the LDO right where it is. Personally I've cut the legs anyway: it saves some power, and it's very easy to solder it again if you need to.

P.s. read this, it contains any information you need: http://www.daveakerman.com/?page_id=1294
Eng. Hazem Habbab wrote:Hello dear, why dont you use a step up Dc-DC converter to rais the 3.3V to 5V anf then u can feed it to your Raspberry PI easily?
Well, if you want real battery life you need to use at least 4 AAA, and that's 6V, so in any case you're going to need a step down DC-DC converter

realworldnumbers
Posts: 5
Joined: Mon Dec 02, 2013 2:28 am

Re: Running Raspberry on 3.3 V

Fri Dec 13, 2013 7:56 pm

DC to DC "convertor" or "Voltage Regulator" has it's drawbacks. I'd recommend using AA (not AAAs) and even then, consider going direct without "power regulation". I did an experiment. I have succesfully powered my Pi and done a test on how long it can survive using only 4AA batteries :D

http://realworldnumbers.com/how-to-test ... batteries/. I got about 8.5 hours and there was no damage when pushing 6.52Volts until fully drained.

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jojopi
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Re: Running Raspberry on 3.3 V

Fri Dec 13, 2013 10:58 pm

realworldnumbers wrote:DC to DC "convertor" or "Voltage Regulator" has it's drawbacks.
You only appear to have tested with a 7805 regulator. That is poorly suited because it is an inefficient linear type and has a relatively high dropout voltage. A switch-mode DC-DC converter will be much better. You may want to use a different number of cells so that you are always stepping down or up, not overlapping the awkward buck-boost region.
I got about 8.5 hours and there was no damage when pushing 6.52Volts until fully drained.
You have quoted the FAQ saying that that is not recommended, because the voltage is very significantly too high. You cannot tell with a short test how it reduces the life of the SoC, or the peripherals attached to the board.

If you do want to run without an external regulator, I think you were wrong to dismiss NiMH cells. Whereas alkalines fall gradually from ~1.65V to ~0.8V and are less than ideal across most of their life, NiMH drop from ~1.3V to 1.0V and spend much of their discharge cycle close to 1.2V. The Pi can run perfectly well at 4.8V or even less. Only its downstream peripherals might be unhappy.

This thread was about the possibility of running the Pi on 3.3V. Amongst other things, that could eliminate the losses in the main onboard linear regulator, RG2. A linear regulator drops excess voltage by wasting it as heat, whereas a switch-mode DC-DC converter changes the voltage by converting it to magnetic flux and back.

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EUA
Posts: 5
Joined: Sat Jul 06, 2013 11:21 am

Re: Running Raspberry on 3.3 V

Wed Jan 08, 2014 3:54 pm

I just wanted you know that:
I run my Raspberry PI modal A with just 3.0v on 3.3v rail without any single issue.
I removed 3.3v Linear Regulator and replaced with 3.0v step down. Work flawless AFAIK.
Also my WiFi work with that setting. (Yes it's signal reception is dropped significantly but it's working at all!)
Check the SamyGO Samsung TV Hacking Community ( http://www.samygo.tv )

karlkiste
Posts: 184
Joined: Tue Jan 22, 2013 8:50 am
Location: berlin, germany

Re: Running Raspberry on 3.3 V

Wed Jan 08, 2014 5:39 pm

EUA wrote:I run my Raspberry PI modal A with just 3.0v on 3.3v rail without any single issue.
What about the 5V rail? Is it also on 3.0V?

devnode
Posts: 1
Joined: Wed Dec 28, 2016 9:56 pm

Re: Running Raspberry on 3.3 V

Wed Dec 28, 2016 10:24 pm

RPI3 Powers up fine with only 3.3V at PIN #1 of the Header Connector. Wifi and bluetooth also work. USB functionality has not been verified since I do not need it for my application.

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TimG
Posts: 293
Joined: Tue Apr 03, 2012 12:15 am
Location: Switzerland

Re: Running Raspberry on 3.3 V

Thu Dec 29, 2016 1:19 am

Zombie-thread alert!
The power circuitry on Raspberry Pis has changed a great deal since this thread was active. The B+ and subsequent models are much more tolerant of low voltage power (although the 2B and 3B are possibly less tolerant of poor power cables, owing to the increased current consumed).
In any case the drop-out on the newer regulator is so low that there is no need to remove or bypass it.

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