wiiguy
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4x AA

Tue Jul 17, 2012 10:28 am

would this device work well with the rpi ?

http://www.dealextreme.com/p/aa-battery ... 48?item=12

Ravenous
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Re: 4x AA

Tue Jul 17, 2012 11:17 am

Looks like it doesn't have a proper 5V regulator - just a battery box with a USB lead. I wouldn't try it, I would look for something with a proper 5V regulated output.

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Ed Raket
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Re: 4x AA

Tue Jul 17, 2012 1:42 pm

You could use a LDO regulator;
http://en.wikipedia.org/wiki/Low-dropout_regulator

Like.... this one from Farnell perhaps? ;)
http://nl.farnell.com/linear-technology ... dp/1783322

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AndrewS
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Re: 4x AA

Tue Jul 17, 2012 2:02 pm

Ed Raket wrote:Like.... this one from Farnell perhaps? ;)
http://nl.farnell.com/linear-technology ... dp/1783322
Huh? Did you deliberately choose a difficult-to-solder part? ;) LDOs are also available in 3-pin through-hole packages.

Joefish
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Re: 4x AA

Tue Jul 17, 2012 2:16 pm

Looks a bit cheap and tatty, but surely 4xAA NiMHs at nominally 1.2V would be in range?
They might put out more than that immediately after a full charge, and I guess it may be outside the spec and warranty, but it's not as if battery power is going to fluctuate rapidly, so how catastrophic could it be really?

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Ed Raket
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Re: 4x AA

Tue Jul 17, 2012 4:09 pm

AndrewS wrote:
Ed Raket wrote:Like.... this one from Farnell perhaps? ;)
http://nl.farnell.com/linear-technology ... dp/1783322
Huh? Did you deliberately choose a difficult-to-solder part? ;) LDOs are also available in 3-pin through-hole packages.
It does seem rather challengeing doesn't it... Lucky for us there's a 3-pin version :mrgreen:

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mahjongg
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Re: 4x AA

Tue Jul 17, 2012 4:22 pm

A LDO on four 1.2 Volt batteries won't work, 4x1.2 is 4.8 Volt, and LDO's need at least more than what they output. Often something like half a volt more, so they need 5.5 Volt to output 5.0 Volt.
% batteries would give you 5x1.2 Volt = 6.0 Volt, which would work fine, even if the battery outputs dropped a bit to say 1.1 Volt.

Feeding the PI directly on 4.8 volt (four batteries) might work for some time, but is not ideal, as the moment the batteries are not completely full it will stop working. Also the maximum the PI may be fed with is just 5.25 Volt, and a protection device (tranzorb) D17 would short circuit any higher voltage to ground, leading to excessive currents flowing if you try to put more into it.

The earlier stories about the PI working directly on batteries was about the beta version, which had a 6.0 to 7.5V DC input, with a 5V LDO pre-regulator directly after the power input. This idea was dropped for having a mini USB port without any pre-regulation for 5V. This beta version would have worked with four 1.5 Volt (not 1.2 Volt) regular batteries, as they would have provided the required minimum of 6 Volts.

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alexeames
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Re: 4x AA

Tue Jul 17, 2012 6:52 pm

And don't forget the fact that 1.2 is nominal. NiMH are about 1.35V when fully charged. You need a regulator and a higher cell count - just like the others have already said. :)
Alex Eames RasPi.TV, RasP.iO

jehan60188
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Re: 4x AA

Wed Jul 18, 2012 3:25 am


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alexeames
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Re: 4x AA

Wed Jul 18, 2012 8:08 am

jehan60188 wrote:what about this: http://www.ladyada.net/make/mintyboost/
That looks beautiful, but no, probably not as it says 500mA output and the Pi needs 700mA at minimum to run reliably.
Alex Eames RasPi.TV, RasP.iO

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