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I'm looking for a battery solution for the Beagleboard XM, which requires a 5V power supply. I currently have a simple 4x1.2V AA battery pack, but I'm not particularly satisfied with it:

1) It gets overcharged (~5.2V) and activates the overvoltage detector of the machine.

2) I have to remove the batteries from the pack to put them on a charger every time I need to charge them. I'd much prefer a solution that with no separate parts and one in which you don't need to move the batteries around.

The BeagleJuice is the closest thing I've found to what I'm looking for, but there's no version out for XM yet.

I'm embarrassingly electronics-illiterate, so I don't really know how to go about this. Any help?

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Because of regulator dropout, it will be hard to find an ideal regulator that can deliver >1A from four NiMH cells. Low dropout regulators typically have modest power, high power regulators typically have larger dropout.

I recommend you switch to 6 cells (7.2v); however I just don't use NiMH any more, lithium cells are so much better. Search for "protected 14500" on dealextreme.com, these AA-sized 3.4v laptop cells are awesome. The larger 18650 size is good too.

For 5v regulation, try the "Battery Eliminator Circuit" from a model helicopter (search for BEC or battery eliminator on dealextreme.com or a hobby site such as hobbyking.com). These regulators can handle way more current than you will use. eg http://www.dealextreme.com/p/8s-5a-switch-mode-ultimate-bec-ubec-45214

Don't forget you can use your multimeter to measure how much current your beagleboard is actually using, which will let you know both how beefy a regulator you will need, and how long a battery life you can expect (factoring in the efficiency of your regulator).

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  • \$\begingroup\$ Thanks a ton, I'll try the 14500 batteries. One question: I used a USB-to-5/2.1mm cable adapter when I powered the Beagleboard with the made-for-mobiles charger. I don't have a multimeter easily available to measure the current used, but do you think that the adapter may have decreased the current? AFAIK, it is USB ports that have the 500mA-max limitation, not USB cables, correct? \$\endgroup\$ – donquixote Feb 24 '11 at 5:47
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    \$\begingroup\$ The cable is unlikely to have had much of an effect (although using too-light cable can melt it, DAMHIKT). The phone charger circuit probably had a current limit set too low. I've found the circuits in phone chargers stick pretty close to the example circuit in the regulator chip's datasheet, so it is possible to reverse engineer the charger and figure out which resistor is the current limiting resistor, and change it out for a different value. \$\endgroup\$ – Christopher Biggs Feb 24 '11 at 7:07
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You should buy a Li-on Battery pack which will suffice Beagle needs. They are the best batteries i have worked with.

To charge it, you will need a "Li-ion charger" (DO NOT CHARGE THEM with a normal DC Power Supply), which are cheap.

Regards, Aadeesh

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  • \$\begingroup\$ Thanks for your answer, but that solution does not satisfy 2. \$\endgroup\$ – donquixote Feb 6 '11 at 16:11

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