battery choice?

I would like to buy a 10Ah AGM (Absorbed Glass Mat) Battery to power my arduino in the field.
Should i buy a 6 volt or a 12 volt battery?
I am planning on trickle charging it with a solar panel.
depending on what you recommend for the voltage of the battery, what would a simple home made charging circuit look like?

What should i look for when shopping for the solar panel setup?
Like output ratings etc.

Thanks
Jeff O’Brien

Hmm, 6V or 12V? It will be interesting to follow this.

If it were me, I would consider 6V, put a diode in series (~5.3V) and run it right into the 5V pin - bypassing the regulator.

If you use 12V and go the regulator you will waste a lot as heat.

I've been pretty cavalier with how power the Arduino and it's held up well. (Of course, it's always hard to argue against caution.)

IMHO, John

[edit]Thinking more, if you intend to charge the battery while powering the Arduino, the diode trick may not be enough of a drop for the charging voltage. I'd hate to throw away a perfectly good 7V though. ::)[/edit]

I would go for a switch mode voltage regulator like the AXA003AOXZ, then use a 12V battery. In that way you don’t waste too much power regulating down.

I suspect most of the power systems (chargers, solar panel controllers, etc) are going to be geared toward 12V, so you'll have more options going the 12V route.

Between the 7805 regulator on some of the arduinos (e.g. NG) and the reverse protection diode, you need 7.6V to get 5V out of the regulator. The nominal 6V probably won't run it correctly.

BroHogan, your diode drop trick may not drop the voltage enough (a nominal 12V battery generally outputs 13.6V, a vehicle charges at 14.4V). Besides that, if you need to do ADC, you need a regulated reference voltage to get any sort of sane readings from the ADC.

As Grumpy_Mike points out, a switching supply will be more efficient than a linear regulator, if you're really worried about power consumption.

-j

Hi, Why not use a 7808 (8v reg) with the 12v power source. That way you are not generating as much heat in the reg (step down is lower) and you will always have sufficient to power the aduino. Also you can use the 12v to do some relay switching and power some ancilliaries.

I would go for a switch mode voltage regulator like the AXA003AOXZ, then use a 12V battery. In that way you don't waste too much power regulating down.

Mike,

do you have a link for that switcher? A quick Googling came up with nothing.

Thanks,

MIke

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=AXA003A0XZ&x=32&y=13

The character following the 3A is a zero not a letter O

I would go for a switch mode voltage regulator like the AXA003AOXZ, then use a 12V battery. In that way you don't waste too much power regulating down.

Hi and thanks for the reply I am very concerned about getting the power consumption down.

I'm kind of new to this stuff and was wondering if you could explain the way a switch mode regulator works and the concept behind your recommendation.

Thanks Jeff

OK here goes switch mode supples for beginners.

A conventional voltage regulator works like a big automatic variable resistor, constantly changing the resistance to make sure the voltage on the output is a fixed value. This means that the voltage not being used is "dropped" across the regulator. This is dissipated as heat in the regulator and represents lost power.

A switched mode supply switches a big voltage onto your load and monitors the output. When it rises to the required amount it opens the switch, disconnecting the supply. Then the voltage drops and it closes the switch again. The switch can open and close up to 500,000 times a second depending on the design. Because no extra power is burned in getting something hot it uses much less energy that the conventional regulator. (Yes I know about the volts drop across the switch but this is small compared to a regulator).

So with a conventional regulator a 0.5A load at 5V will draw 0.5A from your 12V battery. With a switch mode regulator (with efficiency say at 85%) you will draw 0.24A from your battery (even though you have a 5V 0.5A load) :)

Hope that makes sense.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=AXA003A0XZ&x=32&y=13

The character following the 3A is a zero not a letter O

Thanks - they're sweet.

I'm kind of new to this stuff and was wondering if you could explain the way a switch mode regulator works and the concept behind your recommendation.

You might find some of my notes useful: http://code.rancidbacon.com/LearningHowToPowerCircuits

--Phil.