[Gta04-owner] battery problems

[H. Nikolaus Schaller]

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, 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.

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.

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.

Hope this helps,
Nikolaus