[olpc-help] Low Battery Shutdown although full battery (problem)

[Emanuel VonAnkh]

Reading up on the OLPC battery info at various OLPC sites, I have come to
the hypohesis
that there may be possible to fix battery by either:

a) Direct hardware intervention (ie. open up the battery)
b) Testing various charge/discharge scenarios...

a) The idea was put forward on some posts that the charge voltage is too
high (what about discharge?), making the circuitry think the battery is full
before it is. One should then be able to insert a resistive diode bridge
limiting the charge current. (Ie a parallel connection of 2 diodes with a
resistor in series.) But I would need the internal schematics for the
battery for this. (Where can i find this?) I also read there is an EEPROM
inside the battery. How does that work? And what is it doing?

b) One old post mentioned the formation of crystals within (LiMH and NiCd)
batteries. If this is also the case for the OLPC LiFePO4 batteries, these
"crystals" would preferably be "melted". Melting is usually done with heat
and thus we should apply heat! :) A second and related fact is that
charge/discharge characteristics strongly depend on temperature. I thus
suggest the following tests:

1) complete discharge at >30 C and recharge >30 C
2) complete discharge at < 1 C and recharge >30 C
3) complete discharge at >30 C and recharge < 1 C
4) complete discharge at < 1 C and recharge < 1 C

My intuition tells me perhaps (1) followed by (3) is the most likely to
succed in getting your battery operating, if it is just a matter of fixing
the internal battery chemistry. However from what Richard says, perhaps this
is not the case.

I would love to hear more input on this...

Finally, I DO NOT TAKE ANY RESPONSIBILITY for what someone may attempt at
home...








*> Richard A. Smith* richard at laptop.org
<community-support%40lists.laptop.org?Subject=%5Bolpc-help%5D%20Low%20Battery%20Shutdown%20although%20full%20battery%20%28problem%29&In-Reply-To=1788cbd00803020831w3722bcdar73cbadc2270a857%40mail.gmail.com>
wrote:

>> the problem is just concerning replacement of a part I'd rather
>> attempt that on my own, rather than having to wait a month or more for
>> a replacement. What is the actual problem?
>> In the battery or laptop or both?
>
>The problem is in the batteries.  On the batteries I've analyzed the
>charge voltage curve is much too steep.  Its crosses the upper cutoff
>and the circuitry in the battery disconnects the cells from the charge
>path.
>
>I have a small collection of batteries from RMAs that I am sending back
>to the mfg for detailed analysis.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.laptop.org/pipermail/community-support/attachments/20080305/93ec8dd0/attachment.htm