n1ywb
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Re: Absolute minimum voltage

Thu Nov 10, 2011 7:43 pm

OK so the nominal supply voltage is +5V. But what\'s the absolute minimum? Presumably the device doesn\'t stop working at 4.9V. How low can you go?

I ask because it would be nice to be able to power an RPi from 4 NiMH rechargeable cells, which only have a nominal voltage of 1.2V per cell or 4.8V for the pack, and that\'s at full charge. Will this work?

n1ywb
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Re: Absolute minimum voltage

Thu Nov 10, 2011 7:49 pm

I guess I need to do my homework on NiMH, the full charge voltage is 1.4 and the full discharge is 1.1, or 4.4 for the pack of 4. Will the RPi run on 4.4 volts? What about the 5.6v from a fully charged pack?

mard0
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Re: Absolute minimum voltage

Thu Nov 10, 2011 8:14 pm

I was also thinking about using a NiMH battery pack but i think it would be a better idea to use 5 cells and down regulate the voltage so you would have a constant 5v.

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Jessie
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Re: Absolute minimum voltage

Thu Nov 10, 2011 8:30 pm

I tried to find a spec sheet for the BCM2763 that powers the R-pi and couldn\'t find one. So hard to say. But I\'m going to guess that it will run on far less than 5V, the reason being that there has to be a volatage regulator on the board already. First, the SD card needs 3.3V, second I\'m pretty sure the BCM2763 will take either 3.3 or 1.5V I highly doubt it would do anything other than cook at 5V (although due to the fact that no spec sheet is avalible who knows.)

Warringer
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Re: Absolute minimum voltage

Thu Nov 10, 2011 8:48 pm

Why not go for a boost converter?

jamesh
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Re: Absolute minimum voltage

Thu Nov 10, 2011 8:49 pm

The SoC should keep going on lower voltages, but at less than 5V all your USB stuff would start to fail. You might also have problems with HDMI.
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abishur
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Re: Absolute minimum voltage

Thu Nov 10, 2011 9:07 pm

I don\'t know what the nominal input voltage will be, but I do know that you could put a voltage step up circuit between your batteries and the pi. This way you could input 4.2V DC and output 5V DC. This does, however, come at the cost of some of the current that\'s available and some battery life (let\'s say you lose 15% of expected battery life), but on the plus side you save space with the batteries and you would go over voltage if you added a 5th battery into the mix.
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