[Gta04-owner] Battery charge profile

Christoph Mair christoph.mair at gmail.com
Tue Feb 28 22:03:14 CET 2012

Hi Neil,

I finally managed to answer here:

On Sun, Feb 26, 2012 at 4:45 AM, NeilBrown <neilb at suse.de> wrote:
> On Sun, 26 Feb 2012 00:10:17 +0100 Christoph Mair <christoph.mair at gmail.com>
> wrote:
>> On Sat, Feb 25, 2012 at 11:41 PM,  <d0m1n1k at gmx.net> wrote:
>> > as far as i know the gta04 can run on usb, at least if there isn't too much
>> > activity.
>> > wouldn't that be the preferred way once the battery is charged?
>> > are the components connected in a way that the software can switch between
>> > power sources?
>> This behavior should work out of the box (at least it does work with
>> my device): If I connect the USB cable the power drawn from the
>> "battery" (my laboratory power supply) drops to zero.
> You power supply presumably has different current/voltage characteristics to
> a real battery.

I think the only drawback is that it can't deliver very high currents
in very short time because of the (high) voltage drop caused by the
long cable.

> There are various components in the GTA04 which are connected directly to the
> battery (VBAT), so the voltage they see will be exactly the same as the
> voltage the battery see.
> If the BCI (battery charge interface) provides a higher voltage than the
> battery provides, it will charge the battery, as well as drive the various
> components.
> If the BCI provides a lower voltage, the battery will drive the various
> components and will be drained.
> I don't think it is realistically possible for the BCI to provide exactly the
> same voltage.
> So the battery will always either charge or drain - unless you pull it out.

I removed the battery and connected the PSU directly to the battery
contact springs. Here you can see them:

> What voltage does you power supply provide Chris?  I suspect it is a little
> bit higher than the BCI provides, and it has diode protection against a
> reverse current so it does see any current drain.

I set it to about 4.8V but due to the voltage drop in cables and bad
contacts I measured about 4.2V at the battery connector where it was
connected to. (I did not use the AC charge path). As soon as I plug in
USB (5V) the power drawn from the PSU drops to zero.


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