[Gta04-owner] various powermanagement issues

H. Nikolaus Schaller hns at goldelico.com
Sun Oct 18 08:20:13 CEST 2015


Hi,

Am 17.10.2015 um 12:15 schrieb Andreas Kemnade <andreas at kemnade.info>:

> On Fri, 16 Oct 2015 20:05:07 +0200
> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
> 
>>> Monitoring device current:
>>> My last boot from flat battery took >10h even with my bike-approved
>>> initrd setup.
>> 
>> Depends if your device goes to suspend or not. If it does not, it will draw ~400mA.
>> And USB charging is limited to 500mA (unless increased to 800mA). So there
>> are 100 mA for charging of a 1200mAh battery. Should make 12 h.
>> 
> I was not talking about charging the battery full. I was just talking
> about boot(!!) time from
> adding usb power input 

Ah, sorry, I misunderstood.

> The battery is so bad that after precharge the battery has not enough
> power to start booting the kernel most times.


Yes, that is indeed a known problem for a long time. It could be solved by
modifying the MLO so that it turns on 500mA charging within the first 1-2 seconds.

Currently, Linux must boot up to a point to enable 500 mA charging. This takes
30-60 seconds.

Now a discharged battery is charged by ~50mA (trickle charge) until the device
turns on as soon as the battery voltage reaches 3.3V. At that point it may be
charged for just 1%.

If this is not enough for booting to Linux (30-60 seconds @ 400 mA) full
charging will fail.

> So it is really time to
> be replaced...
> 
> root at gta04:~# cat /sys/class/power_supply/bq27000-battery/charge_full
> 389130#

That is indeed very weak. But the bq27000 may also be decalibrated. If I
remember correctly, it needs two full charge/discharge cycles until the
capacity values are "learned".

> 
> 
>>> My battery seems to have lost much capacity the last
>>> weeks. I guess I could still find GTA02 batteries somewhere but not for
>>> a long time. So the questions are:
>>> 
>>> - Are there any other hints for current other than montioring IUOS
>>> mhile in CV charge mode?
>> 
>> bq27000 through hqd should report.
>> 
> Well, I was just thinking about living without the special openmoko
> battery,
> so there is no bq27000.
> 
>>> - Has anyone designed things like a BQ27000 adaptor to put a little bit
>>> smaller standard battery into the GTA04 and that adaptor between the
>>> adaptor board?
>> 
>> Not that I am aware of. But it is an interesting idea! You would just have to design
>> a tiny PCB with two spring contacts on one side and 3 gold contacts on the other.
>> A shunt resistor and the bq27000 in between. Maybe even embedded in the
>> PCB (which should be just 0.5mm thickness...).
>> 
> Hmm, AFAIK the schematics+ of the Om battery are open, so that should
> be a starting point.

Yes, they are but I don't know a link. There is also a "typical application" in the data sheet:

http://www.ti.com/lit/ds/symlink/bq27200.pdf

The package isn't difficult for 2-layer PCB layout.

> 
>> But beware to make it short-circuit *safe*. And, you have to program the bq27000
>> so that it "knows" the nominal capacity. I don't know how easily that can be done.
>> 
> You mean taking care that at least one short circuit protection is in
> the line if you do not know if there is one in the battery?

If there is one in the battery you are fine. If there is none (which is rare for batteries with
hard case), you must take care that the spring contacts are well designed.

BR,
Nikolaus



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