Phone charger (AC vs USB)

[Bun-Bun]

I noticed with my HTC One that charging was significantly slower on my 2A chargers then with my HTC 1A charger. Little bit of research and testing proved that when the HTC 1A charger was used the phone would detect AC charging and when the other chargers were used the phone would detect USB charging.

Now this is all great and dandy, except I want my charging to be FAST.

Using my DMM I compared the resistance between pins comparing the HTC charger to the other chargers. I found that the data pins on the HTC charger were shorted and had infinite resistance to the power pins. However on my other charger there was ~13kohm resistance between the data pins and some high resistance between the data and power pins. hmm...

So I cracked open the 2A charger and found:



Ah hah! Some funky resistor/diode network going on here. Lets just get rid of all that and short the data pins:



I left the other resistor and diode because I was getting tired of de-soldering and they were no longer in the circuit anyway. (And second look the diode may be protection for the charging circuit so I am glad I left them!)



And now my phone detects it as a AC charger!

But it still only charges at 750mA according to battery monitor (HTC charger hit 850mA). I am stumped on that one. Though that is still quite a bit better then the 450mA it was charging at before.

[Bun-Bun]

James Cooper found this link which explains a bit

http://www.ladyada.net/make/mintyboost/icharge.html

My nexxtech charger was branded as a Apple Ipad charger so that would be why it is the way it was.

Further testing last night showed that I was getting 950mA charge from the 2A charger which is better, though still not using its full capacity. But for now I am happy.

Next is going to be finding a Samsung 2A charger (since HTC doesn't make one) and see what happens when I plug it in.

[DigitalOSH]

Is there any way to change this in the software? I have the same issue but far too many USB wall warts to change over

[Bun-Bun]

Not that I am aware. Maybe a custom ROM could accomplish this?

You could make a dedicated "charging" cable.

[erikk]

I'm looking to do something related, wire up a lipo battery to charge phones.
2s lipo with 3A 5V ubec.

I don't think that you can get more than an amp into most phones regardless of the charger. 2A might be an overkill rating for a charger. But with a 3A ubec I should be able to charge 3 phones at once

I'm hoping that shorting the data pins will make any usb device charge at max. Some internet people seem to be cautious but I don't see how any damage to the phone could result. Then again I don't see why cheap 120V chargers don't do that by default (unless they will overheat at fast charges)

[erikk]

Question: will my ubec fry if there's more than 3A worth of phones charging or will it limit the current?

[erikk]

Got it to work, two phones about 1 amp each (Assumed from 0.65 amps on 7.6v side)
The weird thing is that the two phones had different cables that gave them the best current. (they all had shorted data pins)
Also I couldn't get the battery moniter app to get an accurate reading at all.