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

[Rafael Enrique Ortiz Guerrero]

Hi Emanuel,




On Wed, Mar 5, 2008 at 12:04 PM, Emanuel VonAnkh <vonankh at gmail.com> wrote:

>
> 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?
>

Take a look at

http://dirakx.blogspot.com/2007/06/1-wire-protocol.html

also take a look at the OpenEC proyect on the wiki..

http://wiki.laptop.org/go/OpenEC

hope it helps..

>
> 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
>

i'd like to coment more about these steps but i think that a hardware hack +
heat would't  be enough to fix the battery, i guess these are manufactoring
errors.


PS i'm not the expert these are only opinions based in what i've researched
about OLPC's batteries. (Richard would know better)

>
>
>
>
>
>
>
> *> 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.
>
>
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>
>


-- 
Rafael Enrique Ortiz Guerrero
One Laptop Per Child
rafael at laptop.org
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