Minimal Input Voltage



I want to power a Raspberry Pi A+ with a 2S (2x 3.7V) LiPo battery on a quadrocopter. A full LiPo provides 8.4V, but voltage can drop to 6.4V or even 6.0V. I guess Battborg is not suitable for this purpose because of the 7V limit? Or is there a way to make sure that the Pi gets enough power even with this power source?

What happens when the batteries are empty? Is the Raspberry Pi just crashing then oder is there a mechanism to prevent this or some sort of low voltage display?

Best regards,

piborg's picture

Yes, you are quite correct about the 7V requirement. A quick look on the web shows some discharge curves for Lipo batteries to be at 3.5V at about 75% of their cycle. eg.

So I'd imagine you could use them for a while, but it wouldn't be ideal.
If you add another 3.7V cell in series, it would be well within the range, and better suited.
In our tests, sometimes the Pi simply turns off and doesn't come on again. In other tests, the battery voltage slowly builds back up a little, and after a while the Pi tries to reboot once more (normally failing and turning off again some time into the boot cycle. In theory you should try to avoid this situation. In practice, we haven't noticed any problems with this. The most likely problems are that it could cause a file system error and force a disk check.

You could use a step up converter, which will give you the required 5V from a single 3.6 (this happens in a lot of inexpensive USB battery packs), however it isn't as efficient as down conversion and you will most likely get a significantly lower battery life.

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