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To start, I am a software guy, and I really want to ensure I not going to destroy any components. I previously looked at power through a USB power bank, but the issue with these is that they turn themselves off with low current pull.

My question is: I have a number of Arduino shields and would like to power them with 4 rechargeable AA batteries, and therefore would like some advice on what to use without frying any electronics.

The rechargeable batteries I have are these 1.2V AA (NiMH). Going on their rated value they should supply 4.8V. Testing the 4 batteries in serial gives me 5.3V overall, or around 1.325V per battery at full charge.

So if the batteries provide more than 5V, I cannot safely plug them into the 5V pin on the Arduino. But if the batteries could potentially provide around 4.8V to 5.5V plugging them into VIN means that the voltage regulator will take too much power, reducing the overall voltage to be too low for all of the shields (Which require 5V). What should I do in this situation?

This is a list of the current equipment that will require power:

The shields will be stacked on top of each other.

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  • Check the absolute maximum ratings for the main ICs and modules on those boards - you will most likely find that they are fine up to 5.5V, except those that take 3.3V of course. The only issue you may have at 5.5V is a 3.3V device sending data to the Arduino may not have a high enough voltage on the HIGH logic level to register on the Arduino so will need a level shifter. – Majenko♦ Aug 15 '16 at 16:27
  • Hey, I asked a very similar question and just saw yours. Did you end up using an UBEC? – Sertalp Bilal Mar 24 '17 at 5:49
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    I did end up using a UBEC and it worked great! – Calco Mar 24 '17 at 9:08
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Most 5V devices will function fine at up to 5.5V - however, check the datasheets for the major components and modules on the boards.

The main thing to watch though is that a 3.3V device, which can normally communicate fine with a 5V one, may not be able to. The problem is that the logic HIGH signal from the 3.3V device may be below the threshold for a logic HIGH on the Arduino:

V_IH = 0.6Vcc = 0.6 x 5 = 3V

V_IH = 0.6Vcc = 0.6 x 5.5 = 3.3V

Thus a 3.3V device would have to output at the very minimum 3.3V as a logic HIGH in order for it to register as one on the Arduino, which may be a problem...

You can easily drop the battery voltage by 0.7V though by inserting a single silicon diode (such as the trusty 1N4001) in series with the batteries. That will take your voltage down from your measured 5.3V down to 4.6V which will improve matters somewhat.

However, it is important to note that you have so far measured the open circuit voltage of the batteries. That is, the voltage with no load on them. The voltage will most likely be lower once they are actively driving the Arduino etc.

The Arduino itself will be fine running off 5.3V, so I suggest you power just the Arduino direct into the 5V pin from the batteries and measure the actual voltage while powering the Arduino. That will give you a more accurate voltage reading. Then, if needed, you can add the diode to drop it by 0.7V.

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  • The sim module I am using (this one) lists a max voltage of 5.2V. The other 2 boards say they take Arduino 5V and regulate it down to 3.3V (can't find a max voltage). Would it potentially be better to use 6 of the same AA batteries in the VIN pin, giving around of 7 - 8V regulated down to 5V on the Arduino? – Calco Aug 15 '16 at 17:57
  • Using the in-built regulator is wasteful. You'd be better off using a switch regulator from 6 batteries (search: UBEC). – Majenko♦ Aug 15 '16 at 18:00
  • So using a UBEC such as this would allow me to wire from 6 AA batteries -> UBEC -> 5V Arduino pin, with a maximum available current of 5A for Arduino and shields (of which I should only need max 2A)? – Calco Aug 15 '16 at 18:38
  • Yep, that would be ideal. Feed it at least 6.6v and you will get lots and lots of 5v power. – Majenko♦ Aug 15 '16 at 18:41
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    @Gerben My regulator of choice for battery operation is the TC105 - 57µA quiescent, 92% efficient. Runs a sleeping PIC32 off a PP3 for a year. – Majenko♦ Aug 15 '16 at 19:18

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