[Gta04-owner] bq27000-battery: battery is not calibrated! ignoring capacity values

Dr. H. Nikolaus Schaller hns at goldelico.com
Tue Feb 5 09:22:34 CET 2013


Am 04.02.2013 um 16:12 schrieb Bob Ham:

> On Mon, 04 Feb 2013 12:18:25 +0000, Bob Ham <rah at settrans.net> wrote:
>> On Mon, 4 Feb 2013 17:06:54 +1100, NeilBrown <neilb at suse.de> wrote:
> 
>>> The first is if the BQ27000 in your battery doesn't think that it is
>>> calibrated.
>> 
>> I think this is the case.
> 
>> My battery was from a GTA01 developer kit
> 
> 
> On the other hand, perhaps this isn't the problem.  Looking at a
> battery-related page on the Openmoko wiki:
> 
> Temperature control
> gta01, BL-5C, BL-6C	thermistor
> gta02			bq27000 
> 
> --
> http://wiki.openmoko.org/wiki/Battery_Questions_and_Answers#Hardware_capabilities
> 
> Apparently there are two types of battery, one for the GTA01 and one for
> the GTA02.  My battery has never had a BQ27000!
> 
> 
> This raises a big issue: there are two battery types in the wild for the

Yes.

> GTA04 but all the GTA04 software (kernel and userspace) seems to assume
> that there is only one type of battery.  This has far reaching

Yes.

> consequences.
> 
> For the moment, the software side limits the use of the GTA04 such that it
> cannot be used effectively when replacing a GTA01 motherboard.

This is just a limitation on GUI side and can be handled by calculating the
fuel level from battery voltage if the bq27000 is n/a.

The charger does not use or require the bq27000 at all. So the battery is charged
and discharged the same way with or without bq27000.

> 
> Further than that, looking at sheet 5, "Clock and Charger" of the
> Schematics section of the GTA04A4-4 system manual, I see the words "Battery
> contains BQ27000".  This is quite alarming.  Nikolaus, can you confirm that

> the GTA04 will operate safely with a GTA01 battery containing no BQ27000? 
> Particularly, will it charge safely?

It will charge because this is controlled by the TPS65950 using its own
voltage measurement and measuring/limiting the current flowing into the battery.

So you can not overcharge or damage the battery *by normal operation*.

But since you ask for safety: I think, yes there is a small potential risk that we should
be aware about.

Although the Neo1973-Battery has a NTC presented on the middle pin
it is *not* connected to the TPS65950 charger and you will see an almost
constant "battemp" value.

So the charger can't detect if the battery becomes too hot for whatever reasons.

Normally it would shut off charging if the battery reports >50 °C or so, because LiIon
batteries should not become hotter than 60 or 70 °C.

The potential risk scenario is that a (partially) damaged battery is being charged and does
never reach the end-of charging voltage and gets hotter and hotter until ignition
and the charging controller has no chance to recognize and react accordingly.

Or if the device is sitting in full sunlight while being charged. This should be avoided!

But now you may ask how this works better with the GTA02 battery with bq27000?
It also lacks the thermistor connection and therefore the TPS65950 doesn't know likewise.

So there is no difference w/o or with bq27000 in the battery. And there is no
difference between GTA01, GTA02 and GTA04 being used as charger.

I.e. all combinations are on the same safety level.

Nikolaus



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