I have a junk cigarette lighter charger burn after 1 yr of usage, so I am salvaging it for this small project. My research from QualComm found that the phone has build-in battery charging management circuit, and not relying on external power adapter, or computer USB port. I made a brave assumption that Samsung Galaxy Note 2 also has build-in charging circuitry, therefore I can plug in any 5V power supply that I want. I am more confident with proper electronic voltage regulator then unknown China phone charger, especially cigarette lighter charger.
The 2 weeks journey starts by ordering a pre-fabricated 5V 3A voltage regulator from eBay. It is made in China, but I have better fate in proper IC then poor quality charger. For the cable, I have the old cable that attached to cigarette lighter charger, as well as thicker cables laying around. The internal phone charger circuitry has its API expose in Android API, and I found app "Galaxy Charging" to be able to detect the avg/ref/max current, so I don't need to connect it to expansive multi-meter, which I already have one that can measure up to 20 A.
After the parts arrived, It took 4 days to assemble and test everything. The testing mainly to give me more low level understanding of the charging rate, as well as any short circuit protection (over current) in the power supply.
The testing concluded my research that:
1. Connecting pin 2 and 3 (used for data communication) in USB port is the way the phone decide whether it connects to computer (draw less amp), or AC power adapter (draw more amp)
2. Samsung phone charger 5V power supply has some resister in pin 2 and 3 which allows the phone to charge at 1000 mA
3. Original Samsung white USB cable is limited to 1000 mA by the build in phone charger (inside the phone), although the Samsung power adapter is rated at 2000 mA
4. If attached Samsung white USB cable to my 5V 3A power supply that shorted pin 2 & 3, it will only charge at 600 mA instead of 1000 mA
5. If attached any USB cable to computer that handle handle 1A, it will charge only at 460 mA
6. Cable itself can limit the current draw
7. When battery level > 95%, the charge rate decrease to half
8. Build-in charging circuit will decrease its rate after 85%, but I still see it detecting 1800 mA all the way to 100% battery level
After 2 days of testing, I concluded that the tiny cigarette lighter charger cable can only handle 600 mA max, although it detected it is AC charger.
The most important fact is that my circuit is comparable with QualComm Quick Charge 2.0, which charge the battery at 1% per 1 min, or slowest is 1% per 1.5 min. Battery charging is analog, so it isn't a constant rate, so I can accept it might slow down to 1.5 min to charge 1% of battery level from time to time.
Following is the charging rate for my Galaxy Note 2 when using computer USB port, vs customize network cable USB adapter
Charging Rate (mA, % in min):
Computer: 460 mA, 1% every 6-9 min
Samsung charger: 1000 mA, 1% every 2-4 min
DIY charger: 1800 mA, 1% every 1 - 1.5 min
The charger have not been tested with 0% battery level, and minimum I tried is 30% battery level. Moreover, the effect battery life due to high current charging is yet to be confirmed. By shorting the pin 3 to 5V (pin 1) and sometimes to ground (pin 5) has logically corrupted the /data partition, which I have to re-format the /data partition, and reinstall all the software
This power supply can easily attach to car's cigarette lighter cable, which always on, and charge your phone to +50% in 30 min
Advice for friends are:
1. Build this instead of cigarette lighter charger because it is reliable, powerful quick charger, and cheap to replace or repair
2. Use it when emergency with low battery, but don't use it for regular charging
3. Don't use it to charge to > 85%
This is not a QualComm Quick Charge 2.0, which has 12V, 9V, and 5V. It is a constant 5V but can produce 3A. As of this writing (2015-08-17), the phone only can handle 5V 2A, although I don't know exactly what phone actually charge at 2,000 mA or higher
- 5V 3A power supply CAD$2.13 http://www.ebay.ca/itm/221422066455?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
- 10 unit of micro USB angle socket adapter CAD$3.99 http://www.ebay.ca/itm/10x-Right-Angle-Micro-USB-5P-Port-Male-Plug-Socket-Connector-Plastic-Cover-/141331120324?hash=item20e7fdc0c4
- Straight micro USB adapter is cheaper, but I like angle due to I put the phone in landscape when using Google Map
- Cigarette charger CAD$0.99 (but I only use it for testing before permanently attach it to the car) http://www.ebay.ca/itm/Mini-USB-Car-Cigarette-Plug-Adapter-Charger-DC-for-MP3-PDA-iPhone4-4S-iPod-Touch-/181811158811?var=&hash=item2a54ca1f1b
- Use any network cable, either old CAT3 or latest CAT6. It can be any cable, such as speaker cable, home appliance cable, but must fit into the micro USB adapter housing