[Power] quick question.. battery

[Richard A. Smith]

On 07/21/2012 07:26 AM, Nicholas wrote:

> 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?

6.5V is the nominal full charge operating voltage which is not equal to 
the charging voltage. With 6.5V you won't ever reach full charge.

Standard charging procedure is contant current of .5C (ie 1.4A) until 
the battery voltage reaches 7.5V and then constant voltage until the 
charge current falls below 60mA.

The XO [1] uses a slightly different procedure which is CC up to 2A 
until we reach just over 7.4V and then CV until the current falls below 
120mA.

[1] Overall. Each generation of the laptop has a slightly different 
behavior due different charging hardware.  And of course the XO's 
monitor the temperature of the battery and back off it rises above 40 
degC.  But you have to talk 1-wire to get that info.

-- 
Richard A. Smith  <richard at laptop.org>
One Laptop per Child