Battery Power Options

Hi,
    I am trying to figure out a battery solution for my Beagleboard
and I haven't seemed to be able to find anything will Google-ing
around. We are looking to add two additional codecs to the board that
will cause it to have to run (at times) up to 700mA, but at the same
time would like to only use the mini USB to mainly power the device
i.e. use the battery only to pick up the extra 200mA that the usb
connection cannot take. Also, we would like the usb connection to be
able to charge the battery when it is able to. Does anyone have any
experience with this and can point me in the right direction?

Thanks,
Bob

Using the battery to pick up extra current is not really practical. Normally you run off the battery or use it in a charging mode to where the battery is being charged while running off of your DC source. You would be better off just getting a dual headed USB cable as described in the system reference manual and run it off of two USB slots.

If you want to add a battery curcuit, then you need to have it feed the USB mini connector and have the charging circuit charge the battery when needed. Again, you cna’t get sdome current form the battery and then some form the DC jack. In the end, it would all come form the battery. There are literally 100s of ways to do this. My suggestion would be to look for an EVM that one of the chip suppliers have that would deliver 5V from a battery with a DC or charger input. Then, use that to power the board.

Gerald

Using the battery to pick up extra current is not really practical.
Normally you run off the battery or use it in a charging mode to where the
battery is being charged while running off of your DC source. You would be
better off just getting a dual headed USB cable as described in the system
reference manual and run it off of two USB slots.

I don't think using a battery to supplement power is that impractical if all
the original poster wants to do is to supplement. It really comes down to
analog power acrobatics so things don't fry. Depending on how long the pulses
at 700mA are, maybe a super cap could help? Would have to do the analysis
with more information then what is posted to get an estimate.

I am trying to build a device that can work as both a stand alone hand
held device as well as a USB tethered device. Given some additions to
the board it needs up to 1A, although it will only need this when it
is performing a certain function and will not be needed all of the
time. While in stand alone mode I obviously need a battery that is
able to supply 1A at 5V. While in tethered mode I would like as much
power as possible coming from the USB cable, with any additional
needed being supplied by the battery. I would like for the USB cable
to charge the battery when possible. Also, I would like the tethered
to stand alone transition to be "seamless". A dual headed USB cable is
not practical in the long term because this is a commercial
application and for such the less connections the better.

Any thoughts?

Thanks,
Bob

Lithium batteries are funny characters. I tend to err on the safety side when I supply advice about batteries,

Gerald

If you need 1A from a 500mA USB port, you need two ports. If all of the power is being used to power the device, then where is the extra power coming from to charge the battery? If nominal current is say 500mA, then that would leave 500mA to be used for the battery, although to charge a batttery, the whole 500mA is not required. You don’t want to charge the battery too quickly and have it over heat.

I still stand by my original thought which was to find an EVM designed to suply the required volatge and current with a USB charge. Give it a realworld try and make sure it meets your needs. Then, incoporate that into you design.

Gerald

Most of the time the Beagleboard will be using less than 500 mA so the
thought is that the extra power could be used to power the battery, or
even to allow it to charge when the Beagle is off. I'll look into the
EVM as well as the super cap design and let you all know how it goes.
Thanks for the help.

-Bob

Bob wrote:

I am trying to build a device that can work as both a stand alone hand
held device as well as a USB tethered device. Given some additions to
the board it needs up to 1A, although it will only need this when it
is performing a certain function and will not be needed all of the
time. While in stand alone mode I obviously need a battery that is
able to supply 1A at 5V. While in tethered mode I would like as much
power as possible coming from the USB cable, with any additional
needed being supplied by the battery. I would like for the USB cable
to charge the battery when possible. Also, I would like the tethered
to stand alone transition to be "seamless". A dual headed USB cable is
not practical in the long term because this is a commercial
application and for such the less connections the better.

Bob:

BB <- battery <- charger <- usb device port.

with this you run from the batt and when plugged it gets charged.

when running tethered, the 500mA from the usb will run right through and
if the BB needs more, the batt will supply that...