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I understand that I can use 4AA batteries and a step down module to get 5V and power the Pi, however briefly. However, now I'm getting real outrageous and want to trying powering the Pi from just 2AA, even if just for 5 minutes.

The deal is, I have a Raspberry Pi working as my dash cam and powered by a USB cord, but I'm guessing the cord may be easily yanked out if I'm in an accident and my video would get cut off mid recording and corrupt the file (it saves in 10s video segments). However, I would like to have 2AA within my enclosure that take over power supply responsibility in the event main power is lost. I know 4AA is much easier, but takes more room. Instead, I want to use 2AA with this DC-DC step up module. As far as I can tell, I can use this module to change my 2AA batteries into 5V.

Am I correct in my understanding? Let's say the batteries are 1500mAh and in series provide 3v, so 3v/5v=0.6 * 0.85(inefficiency) * 1500mAh = 765mAh, which should power the Pi theoretically for nearly an hour, but I'd be happy for 5 minutes. Please tell me if this will work. Thanks!

Ghanima
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jake9115
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2 Answers2

9

Yes, should do

Just double checking the datasheet of the MT3608:

  • if using AA rechargables instead of batteries, mind the lower voltage (cell voltage 1.2 V), but for two cells in series still above the lower lockout voltage (2 V) of the MT3608
  • at very low input voltages the efficiency could be lower than 80 %, the datasheet (p. 5) lists 80 % at 3 V and a low output current - just to keep in mind if the theoretical runtime is lower than expected

As joan already hinted in the comment there is of course also the issue, how this circuit jumps in if "main" power supply is unplugged. Have a look around for UPS solutions to get an idea of how those ciruits work, e.g. How do I build a UPS-like - battery backup - system?

Community
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Ghanima
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4

I also have an outrageous setup, but with way bigger batteries and is in a server setup.

Your idea will work, as stated by joan. What I would do differently is I'd get a power bank instead. Attach said power bank to power so it's always charging. Then, attach the Pi to the power bank's output. Make sure the power bank supports charging and outputting at the same time. Some power banks disable output when charging.

With a big enough bank and a proper setup, your pi can happily run for hours days at a time.

Here are some numbers:

Power bank: 20000 mAh
Setup: Raspberry pi [MODEL] + 200mA camera

Pi 2        = 15 to 30 hours
B+          = 35 to 50 hours
A+ and Zero = 45 to 65 hours

Also, consider proper shielding from heat, since your Pi and batteries are in a car.

If you really want to use your own batteries, consider this. Oh, and this one definitely supports AA batteries.

Aloha
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