[Gta04-owner] Battery charger

NeilBrown neilb at suse.de
Wed Feb 13 22:28:44 CET 2013


On Wed, 13 Feb 2013 20:48:00 +0100 Flemming Richter Mikkelsen
<quatrox at gmail.com> wrote:

> On Feb 13, 2013 10:45 AM, "Rico Rommel" <rico at bierrommel.de> wrote:
> >
> > Am Mittwoch, 13. Februar 2013, 10:08:16 schrieb Benedikt Bär | Relamp.tk:
> > > Hi,
> > >
> > > Anyone knows how many mA the GTA04 needs with GPS on?
> > > I have a charger that provides up to 650mA, will that suffice?
> >
> > It is enough, but on dumb chargers you will need a USB-cable with shorted
> D+
> > and D- or you can try this udev-rule:
> >
> > SUBSYSTEM=="power_supply", ACTION=="change",
> > DEVPATH=="*power_supply/twl4030_usb" ATTRS{1-0048/twl4030_usb/id}=="200k",
> > ATTR{../../max_current}="500000"
> >
> > > How can I check if it's charging (sys-paths)?
> >
> > /sys/class/power_supply/bq27000-battery/status
> > /sys/class/power_supply/bq27000-battery/current_now
> >
> > Problems I noticed:
> >
> > After resuming from suspend power consumption is crowing more and more. It
> > sometimes reaches more than 500 mA with display on and then it doesn't
> charge.
> >
> > If battery charge is below 60% it regularly disconnects USB and does'nt
> > charge. You have to reconnect the charger. I have the suspicion, voltage
> > reduces with discharging battery too and gets to low.
> 
> In case you were thinking about the battery voltage, note that the voltage
> on lithium batteries are stable!! (until it is maybe 3% remaining current).

Interesting theory.  Not substantiated by practice - at least in the case of
openmoko batteries in a GTA04.

See the second attachment to
  http://lists.goldelico.com/pipermail/gta04-owner/2012-February/001687.html

It graphs measured voltage against capacity reported by the bq27000.
While the charge in the battery drops from 930mAH to 720mAH, the voltage
drops from 4.2V to 3.95V.  This is while the battery delivers a fairly stable
230 mA (approx) - that can be seen in the first graph.

So on our hardware at least, the measured voltage on the battery really does
change.

NeilBrown
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