E27006
Posts: 10
Joined: Thu Aug 30, 2012 10:59 am

Re: My RasPi running off AAA batteries

Thu Aug 30, 2012 11:14 am

from the Rpi schematic, the first chip from the microusb socket is an 3.3V regulator, NCP1117 3.3

http://www.raspberrypi.org/wp-content/u ... s-R1.0.pdf

From the datasheet for NCP family, NCP 3.3 version will accept up to 20V on the input, so perhaps the 7805 5V regulator between your battery pack and the usb socket is not needed, the NCP chip may well take a mere 7 0r 8 volts on the input in its stride.

blc
Posts: 465
Joined: Mon Sep 05, 2011 9:28 am

Re: My RasPi running off AAA batteries

Thu Aug 30, 2012 12:12 pm

E27006 wrote:from the Rpi schematic, the first chip from the microusb socket is an 3.3V regulator, NCP1117 3.3

http://www.raspberrypi.org/wp-content/u ... s-R1.0.pdf

From the datasheet for NCP family, NCP 3.3 version will accept up to 20V on the input, so perhaps the 7805 5V regulator between your battery pack and the usb socket is not needed, the NCP chip may well take a mere 7 0r 8 volts on the input in its stride.
If that's the case, the 5V coming from the MicroUSB power socket must also feed the USB ports (and the 3V3 feeds the Broadcom SoC & LAN/USB chip). Meaning that if you feed > 5v into the power socket, you're going to need a 5v power rail somewhere in order to use USB peripherals.

Plus, I'd much rather blow out a cheap regulator/buck converter, rather than risk the components on the Pi's board.

E27006
Posts: 10
Joined: Thu Aug 30, 2012 10:59 am

Re: My RasPi running off AAA batteries

Thu Aug 30, 2012 2:14 pm

Yes you are correct,

I missed the fact that the 5V feeds the USB connectors directly so anything plugged in to the USB keyboard / mouse etc sockets will see that voltage level (risky if excessive)

I also notice that diodes D10 and D11 are incorporated to prevent voltage backfeeding into the chips,

So do keep the 7805 in the feed to keep everything happy and safe!

apologies,

E27006
Last edited by E27006 on Thu Aug 30, 2012 2:21 pm, edited 1 time in total.

blc
Posts: 465
Joined: Mon Sep 05, 2011 9:28 am

Re: My RasPi running off AAA batteries

Thu Aug 30, 2012 2:20 pm

E27006 wrote:Yes you are correct,

I missed the fact that the 5V feeds the USB connectors directly so anything plugged in to the USB will see that voltage level (risky if excessive)

I also notice that diodes D10 and D11 are incorporated to prevent voltage backfeeding into the chips,

So do keep the 7805 in the feed to keep everything happy and safe!

apologies,

E27006
Heh, no need to apologise :)

User avatar
Mortimer
Posts: 923
Joined: Sun Jun 10, 2012 3:57 pm

Re: My RasPi running off AAA batteries

Thu Aug 30, 2012 2:30 pm

The 5V feed onto the RPi also goes directly to the HDMI port, as damaging the HDMI input to an HDTV would also be a costly mistake.
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JPB-HK
Posts: 56
Joined: Thu Nov 22, 2012 5:00 pm

Re: My RasPi running off AAA batteries

Mon Mar 18, 2013 1:42 am

Good to see that you have successfully run off batteries. This is my goal as well. I am using the LD1117 5V to deliver 5V to the Raspberry Pi. I also added the Dallas Maxim DS2745 as a low-cost i2c battery monitor. It works very well and supports a 'gas gauge' for the battery. It includes Voltage, Current, and temperature. I have not yet tried it with batteries, that's next.

John
NCR 310 - ZX81 - Apple II+ - Dell/Intel - Mac mini... Raspberry Pi!

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