Best battery to use?

Hi all,

I'm making an solar powered Arduino weather station and I was hoping for some battery recommendations. Would it be more reliable to use a 7.2V NiMh with the arduino barrel jack or a 3.7V lipo with a DC-DC boost converter? I was also considering a 6V lead acid battery with a power regulating circuit to take the voltage down to 5V. I have an 8V rated solar panel.

Thanks in advance for any help or advice!

Personally, I would reduce the power requirements as much as possible.

Firstly, I'd be inclined to convert the Arduino to run on 3.3V instead of 5V - it's more efficient. http://www.adafruit.com/blog/2011/04/19/tutorial-tuesday-converting-an-arduino-to-3-3v/ (and make sure you use a low-dropout regulator)

I'd then run the system on the 3.7V LiPo.

This I'd charge from the solar panel through a switching buck regulator and associated LiPo charge management circuitry (say a BQ2000 based circuit).

To be even more efficient I'd also consider scrapping the Arduino altogether and maybe using either the bare Atmel chip with the most basic circuitry required to get it going running at 3.3V, or switch away from the Atmel altogether and go for a super low-power chip like the MSP430. Of course, the latter would then mean that you'd have to re-write everything from scratch, and you'd no longer be eligible for help from us ;)

Thank you for your help! I actually considered the msp430 but the arduino ended up being the better platform for my application. Regardless, the power consumption of the TI's are insane! Running a couple weeks on supercapacitors and whatnot.

I'd say go with an Arduino "Pro" (at 3.3V) and use a 3.7V LiPo with an LDO regulator and charger circuit. I think those can be found as single parts these days. Also, follow the advice on this site about putting the chip to sleep, powering off peripherals, etc, to reduce power consumption.

@jwatte: I'm currently using an arduino mega because of the program size and the multiple UARTS so I don't think that option is available to me. However, do you have any more information on charger circuits? Everything I found online have simply been placing a diode in the circuit to prevent the battery from running current through the solar panel.

I would check out Adafruit. I made a solar iphone charger from their parts. Check out the battery charger. https://www.adafruit.com/products/390

madvoid: @jwatte: I'm currently using an arduino mega because of the program size and the multiple UARTS so I don't think that option is available to me. However, do you have any more information on charger circuits? Everything I found online have simply been placing a diode in the circuit to prevent the battery from running current through the solar panel.

When idly researching this problem a while back, I found some nice boost/buck charger control circuit that was almost exactly for this use case. There are a few problems I recall: 1) You really want a particular voltage to charge a LiPo battery. 2) Trickle charging is harmful to the battery after a certain time -- when it's full, it should just be kept at a particular voltage. 3) The output of a solar cell is highly variable, so a real-time adjusting boost/buck regulator will help get what you can out of it. 4) You really want all of the charging circuit to be using as little power as possible.

Maybe Maxim has something like this? Or the "power options" section on Digi-key. http://search.digikey.com/us/en/products/MAX17710EVKIT%23/MAX17710EVKIT%23-ND/2742095 A search for "energy harvesting" or "solar charger" on that site will probably get you something to go on.

Thank you all for your help! I will probably try to use a lipo with a charging circuit, we will see how it works.