[Gta04-owner] How to not charge your GTA04

Andreas Kemnade andreas at kemnade.info
Wed May 23 07:51:30 CEST 2012


I found out some methods to get an empty battery. Well, just not plug it to a computer
or to the charger is a bit boring ;-) So lets be a bit more creative.

1. Using the openmoko charger:
- connect the charger first to the gta04 and then to the wall socket
- disconnecct the charger from the wall socket and connect it again
- have a short power failure

2. Connecting the gta04 to the computer
- use bad cables with a high resistance
  I have found several ones with a resistance between 1 and 2 ohms.
  Depending on battery state, the charger will detect an usb unplug
  at 4.3V or 4.5V usb voltage, and stops charging despite the voltage
  goes up again. If the battery is empty, you'll get the precharge done
  but then the main charge is not enabled. Not every device is so
  picky about the voltage, so you might have considered these cables
  ok. Using these cables for GTA02 is no problem for example.

about 1.
  checking for id resistor and not setting MUSB_SESSION in MUSB_DEVCTL
  if resistor is 102K should help. In all these scenarios,
  the gta04 starts providing vbus by itself and does not notice
  vbus from external.

about 2:
  setting kernel parameters allow_usb=N and the default current to 500mA
  should already help in several cases. And of course: check your
  cables! I'm not talking about extremely long cables here and I have
  also cables which look same like the bad ones but have half the resistance.

So I wish you happy battery discharging ;-)

Andreas Kemnade
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