# Power Arduino Nano from 3 or 4 rechargeable AA NiMH batteries?

I came across another thread, which mentions a 9V block or 3 AA/AAA alkaline batteries as possible source of power for the Arduino Nano.

For environmental reasons I prefer rechargeable batteries, and there AA (Mignon) because of the higher capacity than AAAs (9V blocks too exotic as rechargeable, few people have chargers for those). The problem is that AA rechargeable have only 1.2V, compared to the 1.5V of non-rechargeable AA alkalines.

When it comes to rechargeable AAs thus

3 pcs. = 3.6V
4 pcs. = 4.8V

Attached to the Nano are both following modules, consuming additional power (@ 3.3V):

• RCWL-0516 Doppler Radar Microwave Motion Sensor Module (max. 100 mA)
• CC1101-868MHz Wireless RF Transceiver (<20 mA)

So the questions are:

• 3 or 4 cells? Attached to which input?
• Whats happens if 4 alkaline with 1.5V = 6V get popped in? Another voltage regulator required?

I would go for 4 to Vcc (aka, not using the voltage regulator). If I'm not correct 3,6V is to low to run the Nano @ 16MHz.

Things to notice:

• if the batteries are low, connecting it to USB might cause the USB to charge the batteries a bit. But because they are I think NiMh and are combined close to 5V, I don't expect that to be a problem.
• Don't connect Vin at the same time.
• Is that 1,2V the max voltage of the battery when fully charged?
• No idea how happy the other modules are with the voltage directly for the battery. Look at the datasheet for them. The Nano at least is just fine.

septillion:
Is that 1,2V the max voltage of the battery when fully charged?

Good point. When fully charged they can be around 1.35-1.4V.

Max of an ATmega is 5,5, so 1,35 is close but should be fine.

Well, 41.4V rechargable = 5.6V, which would/should be fine. However if someone pops in fresh alkalines, we are looking at 41.65V = 6.6V. Can the Vcc In deal with that?

Nope.

I've use 4 x NiMH AAs often and never had a problem.

If you have to use alkalines then I'd go for 3 x AA (4.5V) .

Steve

Well, here we are exactly looking at my problem: You can’t predict whether people will pop in rechargeables or alkalines.

3 rechargeables = 3.6 - 4.2V
3 alkalines = 4.5 - 4.95V

4 rechargeables = 4.8 - 5.4V
4 alkalines = 6V - 6.6V

One scenario is too weak, the other too strong.

Yeah, true.

Solution I would use, use 3 batteries, directly to Vcc. BUT, switch to an 8MHz Arduino

Having said that, that's only concerning the Arduino. Still have NO idea if your sensors will also be happy with that.

Not a bad idea. On ebay.com one can find the Arduino Nano v3.x also in a 8 MHz/3.3V nominal power version. Have to check with my project lead if that would work also. Or are those the Arduino Mini/Micro, falsely labeled as Nano? Confusing...

(It's confusing because this one for instance is a Arduino Micro with USB port, whereas I thought the Micro needs an external programmer).

Don't confuse a Pro Micro with a Pro Mini

Yeah, I just dug deeper and learned the differences (32U4 with USB vs. 328P with FTDI, and so on).

The question now is: Which input voltage range does a 8 MHz, 3.3V Arduino Pro Micro have? See also this github-page.

That will be in the Datasheet of the ATmega32U4 Probably under electrical.

Yep, chapter 29.6. 8MHz down to 2,7V

This datasheet speaks of 3.3V @ 500 mA Vcc, with an absolute maximum at Vcc of 6V.

In other words: With 3 AA cells (no matter whether rechargeable or alkaline) I’m well within range, according to my above numbers. Correct me, if I’m wrong.

Next question is: I assume that 500 mA is the maximum amount of power this board draws, if everything’s connected and controller computing like crazy. How many mA are we looking at average or minimal consumption?

Think those number apply to the onboard voltage regulator. But for battery power you want to try not to use it (because it wastes energy).

And about power, very hard to say. Reaaaaaaly depends on what you do with it. And even more on what you connect to it. Datasheet has some numbers but they will vary. Same chapter

According to how I read that datasheet, there’s really a 3.3 to 6V range on Vcc, so not involving a voltage regulator. It says Raw (so with voltage regulator) is 4-16V.

First note you are NOT looking at a datasheet Merely a spec sheet.

And yes, the 6V is indeed the absolute maximum (aka, no margin at all) voltage for the ATmega directly (aka, no voltage regulator), safer to stay under 5,5V. But you are mixing some things. Nowhere does it mention 3,3V as a minimum Also, because you can't speak of a fixed current for a micro and 500mA is wayyyyyyyy more then the ATmega will ever draw we will have to assume they do talk about the voltage regulator there. Same for the 3,3V to be the normal Vcc (aka, from the voltage regulator).

And digging deeper, that does indeed match with the schematic and the datasheet of the voltage regulator. So my instinct as an electrical engineer is correct

Having said that, 500mA is the max current for the regulator but if you apply a high Vin, the thermal limits of the voltage regulator will be met waayyyyyyy before that!

I stated 3.3V to be the minimum, simply because I couldn’t find a minimum specification. What’s the minimum Vcc at which the Pro Micro still works in your opinion?

But I do understand those figures (3.3-6V) correctly in that both

• 3 pcs. AA rechargeables (3x 1.2-1.4V = 3.6-4.2V) or
• 3 pcs. AA alkalines (3x 1.5-1.65V = 4.5-4.95V)

would actually work?

Wookbert:
What's the minimum Vcc at which the Pro Micro still works in your opinion understanding?

septillion:
That will be in the Datasheet of the ATmega32U4 Probably under electrical.

Yep, chapter 29.6. 8MHz down to 2,7V

Wookbert:
would actually work?

For the ATmega, yep. Sensors, no idea.

septillion:
That will be in the Datasheet of the ATmega32U4 Probably under electrical.

Yep, chapter 29.6. 8MHz down to 2,7V

Sorry, didn’t actually notice that post.

Another question: Do I understand this thread on methods for reducing power consumption on the Mini correctly in that the voltage regulator draws power, even if power supplied via the board’s Vcc pin (e.g. to provide the power for the LED?) In post #11 they are cutting pin 5 (which if it’s an MIC5219-3.3BM5, should be Vout).