[Gta04-owner] Charging battery from USB

Alexander Lehner lehner at edv-buero-lehner.de
Wed Nov 9 18:35:49 CET 2011



On Wed, 9 Nov 2011, Dr. H. Nikolaus Schaller wrote:

> [...]
> The GTA04 also has a problem with USB charging if the battery is
> drained. A low voltage battery is being trickle charged with approx.
> 70 mA. After the power-on voltage (ca. 3.2V) is reached, the CPU switches on
> but then draws approx. 100-400 mA. This of course discharges the
> battery faster than it is being recharged. Depending on some chemical
> effects in the battery and operational thresholds, it may still be
> sufficient to boot the processor far enough that the software enables
> a higher charging current (e.g. 500 mA).
>

Nikolaus,
does the GTA04 power management have the same 'trick' to use a special 
5-pin USB cable to immediately draw 1000mA?
The NEO-charger has this with a certain resistor between ground and the 
'Id-pin' or something like that.

Another solution I've been using was, to boot the phone with a second 
(charged) battery, plug the USB which then allows 500mA charging and then 
exchange the full battery with the empty one.

The philospophical part:
It's nice to understand the current handshaking on USB, I learned a lot by 
reading the NEO wiki.
On the other hand, I never saw a device that obeyed those rules. For 
example coffee-cup warmers or beer-coolers with a Peltier-element and a 
fan simply pull out current of the USB power whatever they can get 
and rely on the hosts power supply to limit current...


A.



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