nice idea. the heater could be an add on, just for the extrem cold areas. yokoy
On Sat, 26 Jan 2008 15:22:57 -0500 "Benjamin M. Schwartz" <[EMAIL PROTECTED]> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Walter Bender wrote: > > 5. Batteries: Carla Gomez Monroy reports from Mongolia that the > > batteries are not lasting as long as expected. The extreme cold was > > the first suspect. Richard had Carla collect data via olpc-logbat and > > ran some tests of his own in the freezer (which isn't as cold as > > Ulaanbaatar). These data, along with a closer examination of the > > GoldPeak data sheet, make it pretty obvious that batteries don't work > > so well in the –20 to –40C range. The extreme cold makes the output > > voltage drop considerably. The result is that at around the 50% > > capacity mark the voltage is so low that the low-voltage cutoff kicks > > in and shuts the laptop off. Richard does worry about when the > > children take their XO laptops outside while suspended; the power > > dissipation (and thus self-heating) is at its lowest. It may shut off. > > The question to work out with our battery vendors is that is it OK to > > de-rate the low-voltage shutoff when it's so cold. Will this do any > > damage to the battery? > > - From the uninformed crazy ideas department: > There's a temperature sensor in the battery compartment. If the EC sees the > battery temp hit -15C, and at the same time the voltage is, say, 10 mV above > the > low-voltage cutoff, it could _resume_ from suspend, in order to increase load > on > the battery, and therefore increase self-heating. This would raise the > battery > voltage and extend battery life. > > Mathematically, if effective battery capacity is reduced by cold, and > temperature is increased by drawing current from the battery, then there may > be > a domain in which drawing current increases the battery's effective capacity. > This approach would work even better if there were a heating element, or > something that could be used as such, near the battery. > > - --Ben Schwartz > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v2.0.7 (GNU/Linux) > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org > > iD8DBQFHm5ahUJT6e6HFtqQRApAeAKChFqO/tK82a7PDBAPMxV6HHbxuKwCeOkZv > qIa4eIwJbYhOhJ9XE7O4EGY= > =jqXT > -----END PGP SIGNATURE----- > _______________________________________________ > Devel mailing list > [email protected] > http://lists.laptop.org/listinfo/devel -- _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
