[OLPC-devel] Battery Charge End Sensing

[James Cameron]

On Tue, Jul 11, 2006 at 02:20:29PM -0400, Jim Gettys wrote:
> OLPC Software Call 07/11/2006  Minutes by Chris Blizzard, edited by Jim
> Gettys.
> - discussion of DCON
>    - discussion of battery and a temp sensor in the battery
>      - if we put a temp sensor in the battery we can determine when 
> we've charged without damaging the batteries - maybe get a lot more 
> cycles but still doing testing

I've not seen a schematic yet, so I've no idea what we've got already,
but I've a few years amateur experience with charging control.

For NiMH charging, delta-V and temperature sensing are required.  Having
a supervisory device record amp-hours is also helpful.

Delta-V sensing often detects the fall in voltage of the first cell
in the pack that has reached capacity.  But if the pack is fully charged
already these falls in voltage may not occur and so temperature sensing
is used ... NiMH releases heat during charge, and releases even more
when overcharging begins.

Begs an additional question ... since OLPC environmental specification
for temperature is so wide, would it be necessary to compensate for
environmental temperature when measuring cell temperature?

-- 
James Cameron    mailto:quozl at us.netrek.org     http://quozl.netrek.org/