[Gta04-owner] battery problems

[H. Nikolaus Schaller]

> Am 18.08.2019 um 16:23 schrieb Andreas Kemnade <andreas at kemnade.info>:
> 
> On Sun, 18 Aug 2019 15:19:22 +0200
> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
> 
>> Hi,
>> 
>>> Am 17.08.2019 um 20:17 schrieb Andreas Kemnade <andreas at kemnade.info>:
>>> 
>>> Hi,
>>> 
>>> I have these kind of replacement "batteries" for the gta04.
>>> 
>>> https://misc.andi.de1.cc/gta04-batteries-small.jpg  
>> 
>> Nice!
>> 
>>> 
>>> The right one works, but dimensions are not perfect and feels
>>> more fragile. The left one worked shortly but then I had no output at
>>> the terminals. There seems to be some problem between the gta04-side
>>> battery - terminal and the B- test point.
>>> 
>>> A picture of the protection circuit is here.
>>> https://misc.andi.de1.cc/prot-circuit-small.jpg
>>> 
>>> As I do not have too much spare protection circuits, do you have
>>> any advice what I should take better care of for the next one?  
>> 
>> The role is to protect the battery cell and not the device powered
>> by it.
>> 
> Well, it is just the best mechanical fitness I have.
> 
>> Well, you can bridge it if you connect an external power supply
>> and not a battery which does not survive a short-circuit.
>> 
>>> 
>>> Furthermore with the right one looking at the display is easier
>>> and I could check current consumption.
>>> 
>>> The whole thing is interesting because it would allow me to run
>>> git bisect run with a closed gta04a5. Currently I am using the letux3704
>>> for it.  
>> 
>> I remember there was a schematics of the HF08 battery (fuel gauge
>> and protector) but I did not find it any more.
>> 
>> Here is an application note by TI and I assume that the HF08
>> battery is not very different:
>> 
>> 	http://www.ti.com/lit/an/slua456/slua456.pdf
>> 
>> Most important is that the current sense shunt resistor and the
>> battery protection FETs are in the - side of the battery. So
>> if there is a GND connection between the power supply and the
>> USB shield this effectively bypasses the protection and the
>> shunt resistor.
>> 
> Well, I guess the shunt resistor is low compared to that bypass.
> 
>> Or did I misunderstand the problem and you are looking for better
>> mechanical design? There you might use three small screws contacting
>> the battery springs of the GTA04.
>> 
> yes, it is about the mechanics. I just want to avoid trashing another
> protector pcb. I do not know the reason why that one got
> apparently damaged.
> The microsd adapter is already better than my screw approach. I
> have checked power consumption of wifi in 2.6.32 (which does not have
> hdq) using such a screw-based adapter.
> 
>> Yet another idea would be to design a new "protector PCB" which
>> only has the three golden battery contacts on one side and some
>> solder points on the other. Since they are quite small, they
>> are not expensive to be produced by e.g. aisler.net.
>> 
> hmm, the contacts are just thing chemical NiAu? Or is hard gold needed
> here?

hard gold just improves mechanical robustness for more plug-in/out cycles.
IMHO this is not relevant here - and if the gold ever disappears you can
take the next PCB :)

BR,
Nikolaus