[Peripherals] Charging the XO off a dynamo
Richard A. Smith
richard at laptop.org
Tue Apr 29 12:24:48 EDT 2008
Arjun Sarwal wrote:
>> Do you think we should tell the OLPC team that their laptop says it's
>> charging when its actually not? Can anything be done for that? Maybe not.
The internal DC/DC converter has a lower power mode where the output
current is limited to about 400mA. This is used for the equalization
phase of the NiMh batteries. I suppose its possible to add some sort of
low power charging mode but the trick is getting into that mode. The
low power mode is not enough to power up the XO. So you have to somehow
tell the EC a head of time that you want a low power charge.
Then there's the little matter that it will take you 7.5 hours of
pedaling to charge the XO from empty to full in that mode.
> Richard __is__ the OLPC team who'd be interested to know about this.
> I'm sure he'd be very surprised to hear what you've described....
Its a double bug I know about just not fixed yet. The EC incorrectly
assumes that if there is external voltage present then there must be
enough juice to charge the battery and its charging. So if you are
connected to a low power device they yellow light will be lit even
though you might actually be drawing power _from_ the battery rather
than charging it.
Then there's a 2nd bug where the the EC will get confused when the
external power comes and goes quickly.
Put these together an you get the symptoms you described.
Richard Smith <richard at laptop.org>
One Laptop Per Child
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