27th April 2012 12:14 AM
Charging a cell phone (Android) from 12v
Hello all. I am new here and did a little searching around before deciding to post this. I am attempting to create converter that will allow me to charge my cell phone (android) from my bike (12v power). I was hoping to be able to create my own instead of just hacking apart a cigarette lighter plug.
My first attempt was with using a 7805 regulator (bench testing with a 12v power supply). In my tests the phone would go into charge and then stop. I had my meter plugged in and was checking the amp pull and when it went into charge it was hitting 1.55A and then it would stop and my meter would go into OL (overload). Then would start up again for about half a second. I presume I am hitting a maximum with the regulator. Here is the circuit I was using for this:
Does anyone have any suggestions as to what I can do to either the circuit or which regulator I can use to get this working?
27th April 2012 12:28 AM
Looking around I found this:
It seems like it could be what I want, but I am unsure.
27th April 2012 12:32 AM
The 7805 is rated at 1A and is probably shutting down due to thermal overload. Try adding a heatsink and a 5Ω 5W resistor on the input to drop some voltage.
27th April 2012 01:35 AM
So dropping the input voltage (the 12v supply) will lower the amperage allowed to the phone? If I can limit the phone to only 800mA I think the 7805 could work. Will adding this resistor to the input do this for me? Or is there another way to limit the current the phone can pull?
27th April 2012 05:12 AM
I know you are talking about an Android, but with the iPod and other Apple devices you can select the charging mode just playing with the Data+ and Data- lines and some resistors
Can Android provide the same feature?
It seems the data lines were gradually adopted as a means for iPhones and iPods to identify the charger that had been connected. By adding voltage dividers to the D+ and D- lines you can instruct the handheld to pull 1 Amp (with data voltages of 2.8v and 2.0v) for wall chargers or 0.5 Amps (2.0v on both data lines) for portable chargers
Last edited by Menticol; 27th April 2012 at 05:17 AM.
27th April 2012 12:15 PM
I appreciate the reply, however this is a feature of the iDevices and not Android devices. I guess this all boils down to figuring out how to limit the amount of current the phone can pull all while allowing it to pull enough to charge and not just run.
Originally Posted by Menticol
i am new,
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