Charging a cell phone (Android) from 12v

[dilbert9]

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 12b 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?

Thanks in advance.

 

[dilbert9]

Looking around I found this:

http://search.digikey.com/us/en/products/L78S05CV/497-1468-5-ND/585989

It seems like it could be what I want, but I am unsure.

 

[Rleo6965]

Try this circuit. It have 5A output current.
http://www.eleccircuit.com/wp-conte...y-5v-5a-by-7805mj2955-for-digital-circuit.jpg

 

[CocaCola]

I have to ask why when you can get a test proven and designed cigarette lighter adapter for under $1? I understand challenges, but I don't always agree with re-inventing the wheel...

The USB output standard is 500–900 mA and these phones charge just fine with a pass through data cable, so there is no need to give your phone 1.55 A even if it will take it... Rather than give the phone everything it will take, you should consider limiting the current instead...

This is just a random Ebay link, no endorsement, but you can clearly see it's output is limited to 5v @ 500mA, and it serves the purpose... They do say the 'new' version has 1000mA capacity, still bellow what you are pumping into the phone...

http://www.ebay.com/itm/Free-shippi...ccessories&hash=item3a73a42cda#ht_1944wt_1396

Also if you are bench testing use 14.5v to better simulate a running and charging motorcycle battery, the extra 2.5 volts will tax the 7805 just that much more...

If you insist on doing it yourself...

http://electronics-diy.com/schematics/ipod_charger.htm

 

[dilbert9]

I have to ask why when you can get a test proven and designed cigarette lighter adapter for under $1? I understand challenges, but I don't always agree with re-inventing the wheel...

The USB output standard is 500–900 mA and these phones charge just fine with a pass through data cable, so there is no need to give your phone 1.55 A even if it will take it... Rather than give the phone everything it will take, you should consider limiting the current instead...

This is just a random Ebay link, no endorsement, but you can clearly see it's output is limited to 5v @ 500mA, and it serves the purpose...

http://www.ebay.com/itm/Free-shippi...ccessories&hash=item3a73a42cda#ht_1944wt_1396

Also if you are bench testing use 14.5v to better simulate a running and charging motorcycle battery, the extra 2.5 volts will tax the 7805 just that much more...

Well my main purpose for building my own was to build my own enclosure, but it is really hard to turn down what you just linked there. For $.99 you can't beat it.

Another thing I was worried about was that the Android phones recommend at least 850mA to charge (After the new GB update). The charger you linked does state 1000mA, but with something that costs only $.99 how accurate is that? I ordered one and will find out, but I do have my doubts.

Again I agree with your no reinventing the wheel. And if this ebay charger does in fact work I will hack it up since it's only $.99.

Thank you for the replies.

 

[(*steve*)]

The voltage is what needs to be accurate (well within +/-10%).

The current is determined by the load. The supply should be capable of a higher current.

 

[CocaCola]

The current is determined by the load. The supply should be capable of a higher current.

The problem here is that the phone is smart, and using USB protocol on that charging port... The phone doesn't have a single current it will operate or draw from that port, it's supposed to have two way communication with the host telling the host how much juice it wants (within USB specs) and the host will adjust and supply if it can... Since you are bypassing the two way communication the phone is getting greedy and taking everything, doesn't mean in needs everything though...

 

[(*steve*)]

Generally speaking, if the phone doesn't detect any magic to allow it to do anything else, it will draw the maximum permissible from a powered USB port (500mA)

There are some "almost documented" magic voltages/resistances that you can put on the data pins (in the absence of a driver telling the phone what to do) and the idevice will draw one of a number of larger currents.

Most of these Chinese adapters follow these "rules".

 

[dilbert9]

I have read multiple articles outlining what you are saying Steve. I am not using an iDevice though. That mainly pertains to the iPhones and certain new gen iPods. If what you are saying is correct then I am unsure why my phone is attempting to pull 1.5A when it should only be trying to pull 500mA.

I guess what it all comes down to is I need to find a method to limit the amount of current the phone is allowed to pull. If I can do that then I should be fine.

 

[(*steve*)]

Perhaps it uses the reverse logic. Perhaps if it doesn't see logic it assumes it's using a charger.

Find a 5V adapter capable of 2A, it's not that hard.

edit: like this.

 

[Rleo6965]

I just remembered that I modified or solder jumper wire on Car USB Charger for my Omnia2 last 2009. I short pin2 and pin3. I think placing short or resistance will determine charging current. So. I short the it to have faster charging current.
USB PIN Connection.
Pin1 = +5V DC
Pin2 = DATA-
Pin3 = DATA+
Pin4 = GND