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[Reply #15 on:]

I would think an arduino would not be a problem on a battery as long as there were no significant power spikes.

The datasheet says "absolute maximum voltage" is 6V.  What happens if you stick 4 brand new, hot AA batteries that are a little over 1.5V each on there?  Slip a few AA lithium cells in there - they are 1.7V new. It may not die immediately, but you will stress the ATmega and shorten it's life (again, from the datasheet).

Other microcontrollers (including the lower speed, lower voltage versions of the ATmega8/168, as used on the lillypad) can operate over a wider voltage range.  Putting a nominal 3V battery (that you may get 3.2 V out of when it's new)  on a part rated for 6V is no big deal.

Low voltages are bad, too.  I used a 3 cell 4.5V battery to power my arduino and got very strange results when programming (no program uploaded, program was corrupt, even wiped out the bootloader once).

I think the FTDI rs232/usb chip has tighter tolerances (5.5V absolute max rating, IIRC).

Know the datasheet before you start changing the power supply.

-j

[Reply #16 on:]

If you're running an Arduino off battery, you really only need to worry about voltage dropping below a level (as other devices, motors for example, make power demands on the battery).  Since this will cause a reset, or just loss of controller power, it's pretty easy to tell what's happening.
I have my Arduino wired into a bot, with power-thirsty motors.  So I wire the battery to the motor controller, which has a 7805 onboard to provide regulated 5V out; I use this power for the Arduino.

[Reply #17 on:]

I have a similar project (build-in battery charger). It will be for an Arduino BT but I would like that PCB can be used for an Arduino USB.
I found the MAX712/MAX713 circuit: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1666
It can be used to supply the circuit while charging batteries (NiCd or NiMh). You can set the number of cells to charge. But I don't know if it is possible to connect a 9V battery.
There's a lot of schematics on the web, and some with the Eagle CAD files.

For Li-ion, thank you kg4wsv! The Max1551/Max1555 seems really good! http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4002
The problem, it seems it can only supply 280mA. I'm not sure, I didn't well-understand the datasheet.
Do you think we can use this component and link it directly to the Arduino BT or to the Arduino USB throw the USB connector?

[Sorry for my english, I hope that I didn't write too much mistakes. (I'm french)]

[Reply #18 on:]

anyone make progress on this?  I'm putting together parts for a arduino based weather station, and I would really like to be able to make it rechargable via solar power.

This combined with wireless will make it a standalone device.... but how to detect low power and recharge during the day?

[Reply #19 on:]

re: battery voltages 4-7v

check out the max710 from maxim. It's a high efficiency boost + LDO regulator. It accepts 1.8 to 11 volts, and gives 5v @ 250mA (vin=1.8v), or 5v@500mA (vin>=3.6v). Can also supply 3.3v if you want.

The booster kicks in if Vin is less than about 6.5v, and the LDO ensures that little to no noise gets into your application, and can be more efficient than a buck in some circumstances.

Would be *perfect* for powering from a 4 cell nimh or nicad battery, whose voltage ranges from 4v to as much as 8v.

Looks like it would work great in combination with max712 too... sounds like a good project to design properly actually.