Using the ATXRaspi in a battery-powered project ?

[natinusala]

Hello,

I'm building a retrogaming handheld console with a Raspberry Pi, and I would like to use the ATXRaspi in order to provide a single button turn on / shut down button. The Raspberry Pi is connected to a 5" LCD screen (powered via USB) and a Teensy LC (also powered via USB). The Raspberry Pi will be constantly emulating gaming consoles, so we can expect it to use a lot of power too.

I saw on the ATXRaspi documentation that it was recommended to have a 2.5A power supply. I would like to use the Adafruit Powerboost 1000C which can give up to 2A - 2.5A, but I couldn't find any battery pack which has more than 1A.

I guess it will not, but will a 1A battery pack be enough to power the ATXRaspi, the Raspberry PI and the LCD Screen + Teensy ? If not, do you know where I can find a 2.5A battery (and a board similar to the Powerboost) ?

Thanks

[Felix]

Don't confuse AmpHours with Amps. They are different things, the guide refers to the current rating of a power supply, AmpHours is the term you need to keep in mind for a battery.
A battery of say 4V at 2.5Ah is really not the same as a 5V wall adapter that can output 2.5A.
If you plan to boost the battery, then anything above 1Ah should work, that refers to capacity more than how much current it can output. A lithium battery is usually high current, at least 1X the Ah rating (ie 1Ah battery should be able to output at least 1A safely at the rated voltage). If you want to get 2.5A of 5V boosted from a 4V battery, you will need more than 2.5A at the 4V side, so that means you need a hefty lithium battery for instance, something 4000mAh (ie 4Ah) or more. There are many such large batteries out there.

[natinusala]

Ooooooh, I see, thanks a lot for the clarification ! Any battery above 4000mAh will work, so will the one that I wanted to buy, which is 44000mAh.

Is there a way to estimate the battery life time ? If the console only lasts 2 hours before running out of juice, I may directly buy a larger battery, and design the case around it. I may be wrong again, but a battery with higher mAh will last longer, right ? I wonder if I should keep the 44000mAh one, or step up to higher model, which has 60000mAh IIRC, to have a longer lasting battery.

[Felix]

Say your Pi setup draws 2amps at 5V.
Let's say your 44Ah can deliver 70% of its capacity when boosted at 5V. So that's 30Ah.
So it should yield somewhere around 15 hours of running time. In reality that could be 10 hours depending how good the pack is. Or even 20 if its great and the Pi draws less. The more current you need to boost the less efficient the conversion will be so ... to really find out, try a smaller battery if you have one and then estimate by capacity extrapolation.
This is very very rough without even running any formulas.

[natinusala]

Wow that's really more than I expected, I expected something like 3~4 hours of autonomy. I'll give it a try with the 44000mAh battery, which is cheaper (and enough).

Thanks for your help

[Felix]

Make sure you mean 44Ah not 4.4Ah.
You typed 44 thousand mAh which is == 44 Ah. That must be a very large battery.

[natinusala]

Yeah it's 4400mAh, not 44000 

[Felix]

Ok so you're probably looking at 2-3 hours depending on load.
I think with the MightyHat which has 5v boost from battery backup, with a 2.5Ah battery, the last time I tested it was up to 2 hours, but on a lighter load, probably around 1A.
Once battery drops below 3.3V its basically "depleted".

[natinusala]

Yeah, the power boost I'll be using has a 3.3V detection LED to warn users of low battery. 2-3 hours is still good, but not as much as I'd expected. For $10 more I can have the 6600mAh battery pack, which is 50% more so it will last 3-4 hours. I think I'll take this one.