Powering arduino Pro Mini with 7,4V Lipo battery

Hi everyone,

I was going to power up an Arduino Pro Mini with a 7.4v lipo battery but first i've some questions:
-Since,as datasheet says,the optimal power supply for the arduino is between 7-12v,when the battery will discharge below 7v (pretty soon i guess),will the arduino still work or will it stop working/bugging etc?
-If i use a 11.1v battery instead,when it's fully charged,the voltage will be around 12.6v,could this damage the arduino or is it still safe to use it?
-Since Lithium battery can be damaged when discharged below a certain limit 'VL' ,is there a way to cut the power supply before 'VL' is reached?

Thanks in advance.

Arduinos work perfectly well below 5V (but will your peripherals...?)

I think the regulator on the Pro Mini has a lower dropout voltage than 1.4V.

Thanks for the fast reply,right,the Pro Mini 3.3v needs only 3.35 -12 V in order to work,i read the 7-12v from another version of arduino by mistake,thanks!
Yeah,all my peripherals works with 3.3v so there should be no problem assuming that i stop the battery before reaching 3.35v.
Now the other question remains:
-How can i cut the power before reaching a certain voltage? May i need to use a separate circuit?

Thanks in advance.

JackM:
-How can i cut the power before reaching a certain voltage? May i need to use a separate circuit?

You could power all the peripherals through a MOSFET controlled with the Arduino (or even an Arduino pin if their consumption is low enough). When the voltage reaches a certain value you switch the peripherals off, disable all I/O and send the Arduino to sleep. In this situation the biggest power draw will be the power LED on the Arduino (which is removable).

You need to be very careful with LiPo batteries. They require a special charging circuit and the discharge voltage cannot be allowed to drop below about 2.5 volts/cell even once, or it will be destroyed completely. You can get battery protection PCBs from various places, like this: Tenergy PCB for 3.6V/3.7V 1.5A-1.96A Li-ion Battery Pack - Tenergy

Thanks to everyone for the answers.
I was initially thinking of Li-po batteries because i thought that the Pro Mini needed at least 7v as input.
But since it can run with 3.35v i think i’ll stick with 3-4 AAA Ni-Mh batteries avoiding all the problems related
to the Li-po batteries.

I think i will still use a circuit similar to the one suggested by fungus.
@jremington thanks for the link,i didn’t know there were pre-made solutions to the voltage control.

Thanks again!

You could run the Arduino off a single LiPo battery feeding it into the Vcc rather than the Raw input. This will bypass the regulator (thereby making the battery last longer as the regulator sloughs off the excess volatge as heat).
Use a single Lithium ion battery such as these: http://www.ebay.com.au/bhp/lithium-ion-battery or for more dubious cheapies these: http://dx.com/p/ultrafire-3-7v-2500mah-lithium-18650-batteries-blue-black-2-pcs-204545.

These batteries have built in protection that prevents damage through shorts, overcharging and (most importantly for you) over-discharge. They normally cut the power at 2.5-2.7 volts thereby preventing damage to the battery.

The battery will give from 4.2 to 2.5 volts which is within the range to run a pro mini at 8Mhz, bypassing the regulator.

lemming:
You could run the Arduino off a single LiPo battery feeding it into the Vcc rather than the Raw input. This will bypass the regulator (thereby making the battery last longer as the regulator sloughs off the excess volatge as heat).
Use a single Lithium ion battery such as these: http://www.ebay.com.au/bhp/lithium-ion-battery

The battery will give from 4.2 to 2.5 volts which is within the range to run a pro mini at 8Mhz, bypassing the regulator.

Yep. I was thinking of building something to do exactly this (Pro Mini+battery with cutoff) the other day and 18650 batteries look like a good choice. I don't remember reading anything about built-in protection though. Maybe that's only the square "camera" batteries.

lemming:
These batteries have built in protection that prevents damage through shorts, overcharging and (most importantly for you) over-discharge. They normally cut the power at 2.5-2.7 volts thereby preventing damage to the battery.

The battery will give from 4.2 to 2.5 volts which is within the range to run a pro mini at 8Mhz, bypassing the regulator.

Wow,didn't know about those batteries!
Mmmm the problem with those is that i've other 3 components that works at 3.3v connected to the arduino (and 3 led that will drain 60mah in the circuit).So in any case i've to stop the circuit around 3.1-3.3v.
But i'll give them a try,the less batteries i use,the better,if one of those batteries can take the circuit at a working voltage for at least 5-7 hours,i'll use them,it's worth to give it a try.

Thanks.

You can use this step-up/step-down voltage regulator to output fixed 3.3 V through its whole discharge cycle of your battery.

and it will cut off at 2.7V

BillHo:
You can use this step-up/step-down voltage regulator to output fixed 3.3 V

Wow,never heard about those components! (i'm a programmer,only had few works with electronics,have mercy :roll_eyes:)
Unfortunately the shop where i buy components doesn't have that exact board,but it has these:
-NCP1402 that i could use even with 2 AAA for a total of 2.4V
-S7V7F5 that i could use with 3AAA batteries or with a 18650.

Reading the datasheet,both seems to give enough power for my circuit even at low voltages (i will need max 100mah)
At this point i think i could use the S7V7F5 so i can use it with both 3AAA or the 18650,without bypassing the regulator since it give constantly 5V.

Thanks!

At this point i think i could use the S7V7F5 so i can use it with both 3AAA or the 18650,without bypassing the regulator since it give constantly 5V.

If you are getting a switched mode regulator (buck/boost converter) then it is better to use one that outputs the 3.3v that you require and bypassing the cheap linear regulator on the Arduino. Switched mode regulators usually have a conversion efficiency of 90% or greater (and running cooler) whereas the linear regulator has an efficiency of 14-40%. Why boost your voltage to 5 volts (at 90% efficiency) only to have it knocked back down to 3.3 volts (at say <30% efficiency) losing all that power? Running off a plug pack this is fine, but running off a battery you want to conserve power.

If you used a product like this:

it will charge your battery and provides you with a ~90% efficient 3.3 or 5 volt (selectable) output.

(Using a single lithium ion you will avoid charge balancing issues with multiple cells as well as the memory effect of Ni based rechargeables).

@Fungus

I don’t remember reading anything about built-in protection though.

On the ebay link that I gave, they state in the product description whether the cells have a protection circuit or not. On the dx.com links they usually have comments from users whether they are protected or not. If in doubt email the supplier but most of these 18650 cells are protected by default.

BillHo:
You can use this step-up/step-down voltage regulator to output fixed 3.3 V through its whole discharge cycle of your battery.
Pololu 3.3V Step-Up/Step-Down Voltage Regulator S7V8F3
and it will cut off at 2.7V

Hello.

You should not count on this regulator to prevent your LiPo battery from over-discharging. You can find out more information about this here:

http://forum.pololu.com/viewtopic.php?f=3&t=7917

  • Ben

bens:

BillHo:
You can use this step-up/step-down voltage regulator to output fixed 3.3 V through its whole discharge cycle of your battery.
Pololu 3.3V Step-Up/Step-Down Voltage Regulator S7V8F3
and it will cut off at 2.7V

Hello.

You should not count on this regulator to prevent your LiPo battery from over-discharging. You can find out more information about this here:

http://forum.pololu.com/viewtopic.php?f=3&t=7917

  • Ben

Thanks for the info

BillHo:
You can use this step-up/step-down voltage regulator to output fixed 3.3 V through its whole discharge cycle of your battery.
Pololu 3.3V Step-Up/Step-Down Voltage Regulator S7V8F3
and it will cut off at 2.7V

My mistake on assumption that the regulator will cut off below 2.7V

This regulator will NOT protect a LiPo from overdischarging and that a separate protection circuit is therefore required.
It does not enter shutdown mode until the input drops to around 1.8 to 2.2V, it is possible to continue draining your battery when the voltage drops below 2.7V.