[OLPC-AU] XO laptops overheating in power racks

[Tabitha Roder]

On 13 October 2010 11:47, IanCunningham <ian.cunningham at nt.gov.au> wrote:

> We are starting to see some XOs show signs of heat distress while
> being left in the new XO power racks. I suspect it is also related to
> them not being turned off prior to charging and the confined space
> contributing to localized heating.
>

What is your ambiant temperature? Does your charging rack have the chargers
built in? How hot do they get? In Samoa with 30C ambiant temperature inside
a classroom, we had 6 black australian style chargers on a 6 way multibox,
they were at 63, 66, 68, 68, 65, 57 degrees Celsius (measured with a non
contact thermometer). The XOs themselves were hardly warm, even stacked
several high (no racks in Samoa).

You might find that the XOs aren't getting hot because they are packed
together in the rack but because the nearby chargers are heating them.


> What would be an average time to expect the XO to charge from flat to
> full? It may be beneficial to have a timer or an alarm to remind
> people to turn off the power rack and prevent over heating.
>

How long does overheating take? If overheating is associated with charging,
then turning the rack off after charging isn't going to help.

Does the XO 1.5 charge faster than the XO 1? I know it can draw more current
from the charger which would suggest it does. Also, how do you define full?
If you watch the battery voltage and current you will see that the charge
tapers off as it transitions from constant current to constant voltage and
may stay a long time balancing the cells inside the battery if the XO is new
or hasn't been charged recently or the battery is sick. In a charge resource
constrained environment (only 10 sockets and a class load of flat laptops?),
knowing that you've got to constant voltage would be useful (but pulling the
power at this point will prevent the BMS doing it's job).

Tom
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