secretreeve
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Re: using 4 AA batteries to power the Pi

Tue Feb 21, 2012 11:45 pm

liz said that the Pi will run off 4 AA batteries.

but considering the micro usb rails im wondering if anyone can provide me with some details on how to wire up a battery box which uses 4 AA batteries to run the Pi?

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jojopi
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 12:32 am

I think the four AA claim is expressed a little bit optimistically.  You can certainly power the Pi for a few hours from those, but only if you use a 5V dc-dc regulator.

If you use four alkaline AAs directly you will get a voltage varying from 6.4V to 3.2V as the cells discharge.  That is well out of spec for a 5V supply for almost all of the discharge cycle.

If you use four NiMH rechargeable AAs you will get a voltage varying from 5.0V to 4.0V.  That quickly falls out of spec for both USB and the 3V3 regulator.  How tolerant are your USB devices and the LAN9512?

drgeoff
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 12:36 am

secretreeve said:


liz said that the Pi will run off 4 AA batteries.

but considering the micro usb rails im wondering if anyone can provide me with some details on how to wire up a battery box which uses 4 AA batteries to run the Pi?


The micro-USB socket only has the two power wires connected.  You can find the polarity at http://en.wikipedia.org/wiki/U.....ial_Bus.  Wire the four NiMh cells in series.

Joe Schmoe
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:07 am

I think the point is that the Pi can actually handle a fairly wide range of input voltage (although the exact numbers I do not have at hand at the moment).

The USB spec says that "5" means anything between 4.75 and 5.25.

4 NiMhs in series gives 4.8 volts.

4 Alkalines (or good old fashioned carbon-zincs) gives 6 volts.

I assume either of these (or anything in between) would be acceptable to power the pi.
And some folks need to stop being fanboys and see the forest behind the trees.

(One of the best lines I've seen on this board lately)

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Gert van Loo
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:54 am

No 6V! You don't want to go too high. I suggest you stick to 5.25V max.

Joe Schmoe
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:58 am

OK - I stand corrected.  That means that 4 1.5v batteries would *not* be a good idea.
And some folks need to stop being fanboys and see the forest behind the trees.

(One of the best lines I've seen on this board lately)

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alexandru.cucu
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 9:30 am

So will the R-Pi run with 4.8v?
I want to make a simple UPS and this will help a lot because even the most efficient voltage regulators will drain my NiMh rechargeable batteries.
https://launchpad.net/~alexandru.cucu

joeofloath
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 9:39 am

Personally I think five nimh cells (6v nominal) and a 5v regulator would make much more sense than trying to use four.

secretreeve
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:12 am

arent rechargable batteries rated at 1.3v anyway?

also still not sure which of the connectors in a microusb connector to hook up the battery pack to

bredman
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:17 am

Should this reference to AA batteries be removed from the FAQ? Absolute beginners will just try to wire 4 batteries straight into the micro-USB cable.

I expect a lot of work to be done in the next few months in the area of battery/UPS power. Should we create an area in the wiki for this?

secretreeve
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:20 am

an area in the wiki's dedicated to power supplies with sections for shop brought alternatives, home made alternatives and powering from a standard pc would be pretty handy

drgeoff
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:29 am

secretreeve said:


arent rechargable batteries rated at 1.3v anyway?

also still not sure which of the connectors in a microusb connector to hook up the battery pack to


The outer two. Did you look at the wikipedia page I mentioned for which is plus and which is minus.  Or wait until you get an RP and have a look.  The pin going to the fuse is positive.

secretreeve
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:31 am

drgeoff said:


secretreeve said:


arent rechargable batteries rated at 1.3v anyway?

also still not sure which of the connectors in a microusb connector to hook up the battery pack to


The outer two. Did you look at the wikipedia page I mentioned for which is plus and which is minus.  Or wait until you get an RP and have a look.  The pin going to the fuse is positive.


well the link you used just takes you to a "not found" page for wikipedia so no it wasnt helpful lol

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rurwin
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:31 am

Cracknel said:

So will the R-Pi run with 4.8v?
I want to make a simple UPS and this will help a lot because even the most efficient voltage regulators will drain my NiMh rechargeable batteries.
Yes, but... You have no headroom there for losses on the power cable, and your batteries will very quickly lose that 0.05V that is keeping you within spec. So you would have a very low battery life.

joeofloath said:


Personally I think five nimh cells (6v nominal) and a 5v regulator would make much more sense than trying to use four.


Good luck finding a cheap regulator that can convert from 6V to 5V. The 7805 requires 7.5V minimum, and switching regulators are significantly higher in price.

I agree this claim should be removed from the FAQ since it is clearly incorrect.

secretreeve
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 10:34 am

i think someone at the foundation should try running the Pi and 4xAA 1.5v batts and 4xAA 1.3v batts and add some clarification to all of this lol

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Gert van Loo
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 11:13 am

secretreeve said:


i think someone at the foundation should try running the Pi and 4xAA 1.5v batts and 4xAA 1.3v batts and add some clarification to all of this lol



Someone not on the foundation (I am still not officially part of it) will look into running a minimum Pi from batteries: Me.

I plan to remove the on-board 3v3 and 1v8 regulators and replace them with two switch mode supplies. Any other solution is foolish as it will drain your batteries about twice as fast as is required! I have no cost for that solution yet but I estimate it to be the price of about 2-4 sets of batteries.

The first try will be to run a 3V3 board only. (No 5V for USB or HDMI) The board will then only run of 3V3 from THREE AA batteries.

Oh, the switch mode regulators I am looking at have an enable pin so you can do a SW shutdown.

However first I  have to get my Gertboard rev. 2 out.

davidgoodenough
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 11:22 am

Surely the best answer is to use one of those USB rechargers that various battery manufacturers are now advertising, which is designed to deliver a proper USB 5V from batteries.  Like car USB adapters (for those starting with a 12V system such as a car battery backed solar system) they are cheap off the shelf items.

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Gert van Loo
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 11:26 am

davidgoodenough said:


Surely the best answer is to use one of those USB rechargers that various battery manufacturers are now advertising, which is designed to deliver a proper USB 5V from batteries.  Like car USB adapters (for those starting with a 12V system such as a car battery backed solar system) they are cheap off the shelf items.



For a car where you have power to burn it is not a problem. For AA batteries you do not want to throw away half of your baterry life on heating the board.

davidgoodenough
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 11:49 am

Gert said:


davidgoodenough said:


Surely the best answer is to use one of those USB rechargers that various battery manufacturers are now advertising, which is designed to deliver a proper USB 5V from batteries.  Like car USB adapters (for those starting with a 12V system such as a car battery backed solar system) they are cheap off the shelf items.


For a car where you have power to burn it is not a problem. For AA batteries you do not want to throw away half of your baterry life on heating the board.


Given that battery manufacturers compete on the amount of extra power they can deliver to your favourite appliance, I would be surprised if they had not at least tried to deliver the power efficiently.  But I have never taken one of them to bits to look.

secretreeve
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 12:41 pm

so basicaly no one has any solid leads on making a 5.5v 1amp battery pack that will last at least 3/4 hours then?

lol and can i recomend that if your new to computers and/or the world of RC you stay away from lithium-ion and lithium polymer batteries, as these DO have a HIGH EXPLOSION rate when used incorrectly and when they blow up you CAN sustain SEVEAR INJURY.

repeat: LITHIUM ION AND LITHIUM POLYMER BATTERIES ARE NOT FOR BIGGINERS!

that said, i did dive in at the deep end and nearly blow myself to smitheriens but managed to keep it safe lol

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Gert van Loo
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:24 pm

davidgoodenough said:

.....
Given that battery manufacturers compete on the amount of extra power they can deliver to your favourite appliance, I would be surprised if they had not at least tried to deliver the power efficiently.  But I have never taken one of them to bits to look.



I think you don't understand me yet. The power is wasted on the Raspberry-Pi board. Not on the X volts to 5V converter. After the voltage is converted (even if it is converted at 100% efficiency)  you put the resulting 5V into the board. There on the board half of it is converted to heat. To prevent that the regulators on the raspberry-Pi board itself must be replaced.

Joe Schmoe
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:29 pm

Oh, now I get it (I think).  You are saying that the RPi board itself was not designed for maximum efficiency (since it takes a single 5v source and then knocks that down to 3.3v [for most of the actual circuitry - everything but the USB, IIRC]).
And some folks need to stop being fanboys and see the forest behind the trees.

(One of the best lines I've seen on this board lately)

drgeoff
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:43 pm

secretreeve said:


well the link you used just takes you to a "not found" page for wikipedia so no it wasnt helpful lol


Aha!  The full stop at the end of the sentence somehow got incorporated into the URL.

http://en.wikipedia.org/wiki/U.....Serial_Bus

Scroll down to "Physical appearance"

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jojopi
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 1:47 pm

drgeoff said:

Scroll down to "Physical appearance"
http://en.wikipedia.org/wiki/U.....appearance

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Gert van Loo
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Re: using 4 AA batteries to power the Pi

Wed Feb 22, 2012 3:08 pm

Joe Schmoe said:


Oh, now I get it (I think).  You are saying that the RPi board itself was not designed for maximum efficiency (since it takes a single 5v source and then knocks that down to 3.3v [for most of the actual circuitry - everything but the USB, IIRC]).



Indeed. the alpha boards had SMPS but the cost was too high to get a $25/$35 end product. So we had to cut cost and use linear regulators.

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