arm2
Posts: 253
Joined: Thu Dec 15, 2011 3:46 pm

Running a Pi with only 3V3

Thu Dec 17, 2015 2:31 pm

Early on there was discussion that if you don't need HDMI, networking or USB you could run a Pi at 3v3 (powering via the 3v3 pin on the GPIO) has anyone managed this?
I need to design something that will work on Pi1's (and later) that will continue to run whilst accessing GPIO and SD card but with no 5V. I've tried powering 5V and 3v3 then disconnecting the 5V but everything stops. I've also tried powering via 5V and putting some supercaps on the 3V3 line but everything stops immediately 5V is turned off.
Put 5V supercaps on the 5V line and things continue for about a second!
I'm probably missing something obvious.

User avatar
joan
Posts: 14473
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Running a Pi with only 3V3

Thu Dec 17, 2015 2:44 pm

Try powering with 3.3V (or a bit more) into the 5V pin.

clacktronics
Posts: 60
Joined: Sat Mar 03, 2012 6:07 pm
Location: London
Contact: Website

Re: Running a Pi with only 3V3

Thu Dec 17, 2015 2:47 pm

Hey,

I dont really know, but perhaps it is because parts of the chip are not getting the power. If you only power on the 3v3 line that 3v3 cant get to the 5v line which probably feeds the vbat input that is nessesary. look at the compute module powering for clues.

https://www.raspberrypi.org/documentati ... gnguide.md

and schematics of power
https://www.raspberrypi.org/documentati ... matics.pdf

I think you may have tried this already, but put 3v3 on both 5v and 3v3?
My Kickstarter for a analogue AV out - kck.st/1SuGDvV

User avatar
joan
Posts: 14473
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Running a Pi with only 3V3

Thu Dec 17, 2015 2:54 pm

I've used a lipo down to a measured 3.09V to power the Pi from the 5V pin. I was using a serial link to talk via the UART.

User avatar
TimG
Posts: 294
Joined: Tue Apr 03, 2012 12:15 am
Location: Switzerland

Re: Running a Pi with only 3V3

Thu Dec 17, 2015 6:22 pm

arm2 wrote:I need to design something that will work on Pi1's (and later)
Which Pi model are you using, exactly?
I found that a Pi Zero will run reliably at 3.0V. The A-plus, B-plus and 2-B have similar regulation circuitry, except with extra current and polarity protection. Allowing for some small voltage drop across the protection components, I would expect these boards to be fine at 3.3V.
The power circuitry on the earlier A and B models is much less tolerant of low voltages, and in my experience intermittent problems start appearing at around 4.3V (or higher if any peripherals are drawing current).

stderr
Posts: 2178
Joined: Sat Dec 01, 2012 11:29 pm

Re: Running a Pi with only 3V3

Thu Dec 17, 2015 6:40 pm

TimG wrote:
arm2 wrote:I need to design something that will work on Pi1's (and later)
Which Pi model are you using, exactly?
I found that a Pi Zero will run reliably at 3.0V.
Did you find that this reduced the amount of power the device used?

User avatar
TimG
Posts: 294
Joined: Tue Apr 03, 2012 12:15 am
Location: Switzerland

Re: Running a Pi with only 3V3

Thu Dec 17, 2015 7:16 pm

stderr wrote:Did you find that this reduced the amount of power the device used?
335mW at 5.0V
316mW at 4.0V
282mW at 3.0V
All measurements with Raspbian Jessie, CPU idle, LED off, HDMI disabled, no USB device. Uncertainty +/-5mW.

arm2
Posts: 253
Joined: Thu Dec 15, 2011 3:46 pm

Re: Running a Pi with only 3V3

Fri Dec 18, 2015 9:20 am

TimG wrote:
arm2 wrote:I need to design something that will work on Pi1's (and later)
Which Pi model are you using, exactly?
It needs to work on Pi 1's Model B (Rev. 1 and 2) as the project has an installed user base . I'd expect anything that worked on the Pi'1 to work on later models.

User avatar
joan
Posts: 14473
Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: Running a Pi with only 3V3

Fri Dec 18, 2015 9:28 am

arm2 wrote:
TimG wrote:
arm2 wrote:I need to design something that will work on Pi1's (and later)
Which Pi model are you using, exactly?
It needs to work on Pi 1's Model B (Rev. 1 and 2) as the project has an installed user base . I'd expect anything that worked on the Pi'1 to work on later models.
TimG's post indicates that it won't work on early Pis. The post suggests >4.3V is needed.

User avatar
RaTTuS
Posts: 10504
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: Running a Pi with only 3V3

Fri Dec 18, 2015 9:31 am

arm2 wrote:
TimG wrote:
arm2 wrote:I need to design something that will work on Pi1's (and later)
Which Pi model are you using, exactly?
It needs to work on Pi 1's Model B (Rev. 1 and 2) as the project has an installed user base . I'd expect anything that worked on the Pi'1 to work on later models.
it probably will not as the power circuitry is different on the older ones .
I'd say to older ones to upgrade to newer RPi's if it was me
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

arm2
Posts: 253
Joined: Thu Dec 15, 2011 3:46 pm

Re: Running a Pi with only 3V3

Fri Dec 18, 2015 5:52 pm

RaTTuS wrote:
arm2 wrote:I need to design something that will work on Pi1's (and later)
Which Pi model are you using, exactly?
RaTTuS wrote:
arm2 wrote:IIt needs to work on Pi 1's Model B (Rev. 1 and 2) as the project has an installed user base . I'd expect anything that worked on the Pi'1 to work on later models.
it probably will not as the power circuitry is different on the older ones .
I'd say to older ones to upgrade to newer RPi's if it was me
We will have to do two designs then as there are 400+ Pi 1's that need to be run at 3v3. We know that B+ are available now at very reasonable prices but you also have to change the case and change to a microSD card so thousands of pounds.

Sorry if the quoting is wrong it said I had to reduce the quote level

davenull
Posts: 1159
Joined: Thu Oct 22, 2015 7:22 am
Location: a small planet close to Betelgeuze

Re: Running a Pi with only 3V3

Sat Dec 19, 2015 1:25 pm

what about a DC/DC step-up converter? there a lots of models for 1-5V in and 5-12V out,
e.g. sort of
http://www.ebay.com/itm/DC-DC-Step-up-C ... SwSHZWc6wF
#define S sqrt(t+2*i*i)<2
#define F(a,b) for(a=0;a<b;++a)
float x,y,r,i,s,j,t,n;int main(){F(y,64){F(x,99){r=i=t=0;s=x/33-2;j=y/32-1;F(n,50&S){t=r*r-i*i;i=2*r*i+j;r=t+s;}if(S){PointOut(x,y);}}}for(;;);}

Return to “General discussion”