Battery setup

Hello Everyone,

I have a question regarding battery setup, I have 2 pieces of IMR 18350 3.7v 1200mAH batteries and i was wondering which setup would be the best (safe, longer lasting) to power up an Arduino Pro Mini.

  • 2 cells in series, creating a 7.2v 1200mAH battery pack, with a linear 5v and 3.3v regulator
  • 2 cells in parallel creating a 3.7v 2400mAH battery pack, with a step-up switching regulator to 5v and a 3.3v linear regulator

This project is to run a GPS module and save its coordinates in an SD card strapped to the underside of a bicycle.

Its worth checking if the Pro Mini has a low-dropout regulator - a 3.3V Pro Mini might work from 3.7V.

You need to consider how to detect undervoltage - with the parallel configuration direct to a ProMini it is possible the brown-out detection (BOD) level is already set up to do this automatically. You need to check the BOD fuses to see what voltage is set, and check against the batteries safe limits.

The problem with using a boost regulator into a linear regulator is that it will try to drain the battery completely, which is not safe for Li Ion batteries. Some sort of protection measure would be needed.

My first post may be incorrect, as I am not actually using an Arduino Pro Mini, I built my own Arduino circuit based on the Pro Mini Schematic since i have an ATMega328 lying around. The batteries indicate that it has a built in overcharge/over-discharge protection circuit built into the battery. With that in mind, is it still not safe to use a switching regulator with a linear regulator?

Well if its self protecting no problem.

With your own circuit you can choose a low drop-out 3.3V regulator
something with < 0.25V dropout would work well enough I think.

That’s also the most energy efficient - small DC-DC converters tend to be about
80 to 85% efficient, dropping 3.7 to 3.3 is 89% already…

Since I also need a 5v power supply would the regulators best be in series or parallel?

  • BAT > 5V > 3.3V
  • BAT > 5V and BAT > 3.3V