[Power] quick question.. battery

[Nicholas]

OK. Sorry for the terrible question below

It was a leading question. Been charging a loaner 1.75 with the
prototype solar panel today. Done some reading and made some
measurements and had a look at the connectors and it looks good for an
external charger just for way the pin sockets are laid out.

Found the page on the supercharger, and that looks great..

So, thinking about how a low power MPP charger (I made a low cost one
out of commodity parts) might charge this battery externally. Then
looking up maximum termination voltages (from what I found on the web)
for lifepo4 cells come in at 3.65v and somewhat higher for prismatic
cells (again from the web). I did take notice of that "maximum" part.
However 3.25v p/cell is quite a different value to 3.65v p/cell.

I read the battery wiki pages and could find info on external charging
for NiMH batteries. A maximum value of 7.3v supply voltage is
mentioned there and battery voltage to be set to 6.5v.

I know there has been a great deal of work that went in to this
battery system and I have much respect for it and the whole OLPC
project in general--so I know this 3.25v p/cell value has been thought
out through and through.

Reason for going into this is from thinking a cheaply made external
charger might be of some value. My immediate impressions from charging
outside in the sun today is worry for fear of standing on the laptop.
Also, I am being very careful but it would be very easy to damage the
laptop if charging near or on concrete or even wood or hard ground.

My question is if I was to construct a charger to provide for a
maximum of say 600mA at a certain regulated voltage and if there were
a recommended voltage for external charging what would that
recommended supply voltage be? That is, going straight in to the
terminals of the battery.
6.5v?

On 7/21/12, Richard A. Smith <richard at laptop.org> wrote:
> On 07/21/2012 01:13 AM, Nicholas wrote:
>> Hello everyone, I am sorry if this has been covered somewhere but I
>> can't seem to find any info regarding it.
>>
>> I am trying to find out why the full battery voltage on a new BYD
>> LiFePO4 battery is 6.5v?
>
> 3.25 volts per cell and 2 cells in series.
>
> --
> Richard A. Smith  <richard at laptop.org>
> One Laptop per Child
>
>
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