[Gta04-owner] charging log

[NeilBrown]

On Mon, 9 Sep 2013 12:58:30 +0200 Radek Polak <psonek2 at seznam.cz> wrote:

> On Monday, September 09, 2013 01:53:13 AM NeilBrown wrote:
> 
> > On Sun, 8 Sep 2013 19:26:55 +0200 "Dr. H. Nikolaus Schaller"
> > 
> > <hns at goldelico.com> wrote:
> > > Essentially it shows that your USB charging voltage is too low. It should
> > > be ~5V. Maybe you are drawing too much current from the charger or
> > > the cable is weak.
> > > 
> > > There is a comparator in the TWL-usb-chager hardware set at fixed
> > > 4.5V that turns off the charger if VBUS goes below.
> > 
> > Actually 4.4V according to my documentation
> > 
> >   7.4.1.1.3  VBUS Detection
> >   The VBUS presence comparator, which is part of the precharge analog
> > hardware, detects whether a USB device capable of supplying the VBUS pin
> > is plugged in. When VBUS is detected (VBUS voltage is higher than 4.4 V),
> > a communication between the BCI and the USB detects whether the USB device
> > plugged is a USB host, a carkit, or a USB charger. Fast precharge with
> > charger is not supported.
> > 
> > In Radek's logs the voltage is initially around 4.5 but then drops below
> > 4.4 while charging.  It finished the charge at aout 4.4V but it seems this
> > is too low to restart.
> > 
> > My logs show the twl4030_usb voltage between 4.81 and 5.18.
> > 
> > Possibly setting a lower charge current (via those udev rules) might allow
> > the voltage to remain high.
> 
> Yes it seems to help.
> 
> root at neo:/sys/devices/platform/omap_i2c.1/i2c-1/1-004b/twl4030_bci# cat 
> /sys/class/power_supply/twl4030_usb/uevent
> POWER_SUPPLY_NAME=twl4030_usb
> POWER_SUPPLY_STATUS=Charging
> POWER_SUPPLY_ONLINE=1
> POWER_SUPPLY_VOLTAGE_NOW=4475322
> POWER_SUPPLY_CURRENT_NOW=507690
> 
> root at neo:/sys/devices/platform/omap_i2c.1/i2c-1/1-004b/twl4030_bci# echo 
> 250000 > max_current 
> 
> root at neo:/sys/devices/platform/omap_i2c.1/i2c-1/1-004b/twl4030_bci# cat 
> /sys/class/power_supply/twl4030_usb/uevent
> POWER_SUPPLY_NAME=twl4030_usb
> POWER_SUPPLY_STATUS=Charging
> POWER_SUPPLY_ONLINE=1
> POWER_SUPPLY_VOLTAGE_NOW=4810629
> POWER_SUPPLY_CURRENT_NOW=256758

That looks good.

> 
> 
> I didnt know that changing max_current on the fly is possible. Now we could 
> implement quite clever charging. E.g. slowly raising max_current from 100 and 
> checking if voltage is safely above 4.5V. We could also lower max_current when 
> the battery is nearly full and try to keep battery's current_now at 0 so that 
> it charges very very slowly. Does this sound good?

The first half of this is probably a good idea.
The second half won't work.

The number you control is the max current flowing out of the power management
IC.  It feeds the battery, the Modem, and the 1.5V line (via a regulator).
As the current used by those last two vary a lot, the current available to the
battery will also vary.  So I don't think you can really fine tune the
current going into the battery.

Feel free to try though.

NeilBrown
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