[Gta04-owner] battery holder

[NeilBrown]

On Mon, 19 Dec 2011 18:14:35 +0100 Andreas Kemnade <andreas at kemnade.info>
wrote:

> Hi,
> 
> as there seems to be again problems with empty batteries and charging the
> gta04.
> I am thinking about printing a separate battery holder (I own a reprap) to be
> able to charge the battery externally. How do I make stable contacts to the
> battery? The electronics is not the problem.
> 
> Or is the problem with empty batteries already solved? Unfortunately I have no
> GTA04 yet to try it out. I hope that situation changes in the next days.

It isn't solved but I have hopes of solving 99% of the problem.

My experience is that if you leave a flat battery for a while it will gather
up what charge it has and be able to deliver it - maybe only for a second.
That much time should be enough for uboot to enable the battery-charge
interface and run off USB power.

So we would need to make sure that uboot enables charging very early, and
make sure that Linux doesn't disable charging - even for a moment.

One problem with this is that it is not correct to draw current from a USB
cable unless we have determined that current is available, and determining
current availability from a PC is (I think) a bit more complicated than uboot
should be.  Detecting a charger is easy so you might need to use a charger to
charge a nearly-empty battery.   I still have stuff to learn here though.

Currently the device doesn't charge when off because we turn the battery
charger off.   That should be easy enough to fix.

Also the gta04 board has the  possibility for being provided stable current
and booting from that with no battery.  This current comes in through the
same port that the serial cable is connected to.  I cannot think of a way to
provide power through that port but if you could, you could charge a
completely flat battery.

NeilBrown
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