maemo.org - Talk - View Single Post - Charging with aftermarket Chargers/cables

quanttrom	2013-09-10 , 22:32
Posts: 50 \| Thanked: 36 times \| Joined on Aug 2010	#1

Hello guys,

I have been battling with weird charging problems on my phone. The phone will show as charging but in fact it will NOT be charging and instead slowly depleting the battery. Finally last weekend I sat down determined to get to the bottom of this. I haven't been able to narrow down exactly why it happens. This is where you guys might be able to help but I am fairly certain I have a solution for the time being.

My current setup involves using the N900 as a motorcycle GPS. The screen is always on, sometimes for hours so constant charger capable of relatively high current draw is absolutely a must.

I inspected and looked at the whole charging system of the motorcycle, everything appeared normal. I purchased a charger capable of 2A @ 5V and tested it. It is in fact capable of delivering the rated current with acceptable voltage drop. I tested it. Everything appeared normal as well. Finally i set my eyes on the N900 because initially I did not believe it was the culprit.

Just to be on the safe side, I shorted the D+ and D- pins of the USB with a solid wire. I don't use the USB port for anything else other than charging. The ground pin on the USB was further connected to the ground plane and finally the VBUS on the USB connector was connected to the fuse with a direct wire connection. I glued everything in place in order to avoid any potential issues due to vibration.

I started looking at low lever I2C scripts capable of reading the charging and gas gauge ICs of the N900.

What I found out is that sometimes the BME will somehow instruct the battery charging chip to limit the charging current at 100mA. This is not adequate to power a screen and CPU intensive application such as GPS.
Through monitoring the current going through the battery gas gauge I was able to narrow down when the phone is actually charging and when it just appears to be charging.

I started out with a script made by jeorg_rw:
http://talk.maemo.org/showpost.php?p=658278

and monitoring the charging current with bq27200.sh script by shadowjk

eventually I realize that no matter what I plugged in I can coax the phone into charging with only a part of jeorg_rw's script:

Code:

i2cset -y -m 0xff 2 0x6b 0x02 0x8c;
# 0x8c = 3v5 + .640 + .040 + .020 = 4V200, BE CAREFUL and DON'T CHANGE
# unless you know what you're doing. 4V2 is ABS MAX!


i2cset -y -m 0xff 2 0x6b 0x01 0xc8;
echo "Charing parameters set..."

I run this and I DO keep BME running through the whole ordeal. I have NO idea how this affects BME and BMEs interactions and internals but it does not SEEM to cause any issue. It is entirely possible that BME and this crude I2C interaction can clash and cause unpredictable results.DO NOT do anything you are unsure of...This is at best a "hack" !

The first line sets the max charge voltage and the second one starts the charging process with no current limit..(hmmm)

I created myself a small script that lets me execute this whole ordeal easily every time I plug in a random charger.

/home/user/adjust_current.sh

Code:

#!/bin/sh

# gain superuser rights.

if [ `id -u` != 0 ] ; then
    exec sudo gainroot <<EOF
exec sh $0 $*
EOF
   exit $?
fi

# put your code below

i2cset -y -m 0xff 2 0x6b 0x02 0x8c;
# 0x8c = 3v5 + .640 + .040 + .020 = 4V200, BE CAREFUL and DON'T CHANGE
# unless you know what you're doing. 4V2 is ABS MAX!


i2cset -y -m 0xff 2 0x6b 0x01 0xc8;
echo "Charing parameters set..."

I also created an icon so I can easily start this:
/usr/share/applications/hildon/adjust_current.desktop

Code:

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Terminal=true
Type=Application
Name=Adjust Current
Categories=System;TerminalEmulator;
X-HildonDesk-ShowInToolbar=true
Exec=sh /home/user/adjust_current.sh
Icon=/opt/usr/share/icons/hicolor/scalable/hildon/statusarea_battery_insufficient_charging.png

I execute this "app" every time I connect it to an "eBay" style non-Nokia charger.

What is funny is, the wall charger will consistently and reliably charge the phone EVERY TIME. Maybe the ID pin is involved somehow, I am not sure and at this point in time I am 100% satisfied with my hackjob solution as it does what I want it to do and I have already spend enough time chasing this.

Do you know what might be causing the charging issues shown above? Is there a proper fix?

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