USB charging current detection - Page 1
Forum section: electronics / beginners

author: Luckymat
author_rank: Contributor
timestamp: October 07, 2013, 03:48:42 pm
content: Hi guysI want to make usb charger powered by battery 6x AA 1.2v rechargable Ni-MH 2500mA/h Vipow bateriesI want to power it of battery becouse its easier to buy 6x AA 1.5v batteries than charge these(Its just more portable)So i have already case,batteries,battery pack,lot of wires,and USB port and a step down converterIf i hook anything up i have 5v (+/- 0.1v) power supply that can supply like 2ABut if i hook my phone it charges at 499mA and it should charge at 999mA or moreI know that i need to connect anyhow D+ and D- and shield and ground but i have no idea how to...I already googled it...and i did'nt find mouch...MY PHONE IS EXPENSIVE AND I DONT WANT TO BLOW IT UP(samsung galaxy s3)If somebody needs photos i can make some and post itSo i hope anybody anwser and help...(Sorry for my bad englsch...im from poland)

author: andtfoot
author_rank: Unknown
timestamp: October 07, 2013, 04:04:09 pm
content: Shorting the D+ and D- pins (the two middle ones on a normal A connector) together on the USB port from the charger is a common way of telling the phone it is connected to a charger.There are exceptions based on phone model, such as the Apple stuff, which need a particular voltage or resistor network present.Edit: There are some more details in the datasheet I just found for a USB charge controller chip:http://www.ti.com/lit/ds/symlink/tps2514.pdfPage 10 has what I was talking about (DCP Short Mode).

author: jakehiltz
author_rank: Contributor
timestamp: October 07, 2013, 05:03:12 pm
content: you can also just use (I believe ) a 4200ohm resistor

author: olsenn
author_rank: Frequent Contributor
timestamp: October 07, 2013, 05:13:17 pm
content: You're wasting batteries, but that's your decision.According to the USB specification, dumb chargers (ones that don't digitally handshake the output current capabilities) first short the supply to see if >1.5A can be sourced, and if it can, it uses 1A. If it cannot, it defaults to 0.5A (which is how much a computer's USB port can provide)

author: Luckymat
author_rank: Contributor
timestamp: October 07, 2013, 07:45:27 pm
content: Quote from: olsenn on October 07, 2013, 05:13:17 pmSo what's another ideato not waste batteries?so i can just short D+ and D- and connect Vcc and GND and if my phone sees 1.5A it just draws so much?and if i limit current to 1A it draws 1A?if i just connected shield and GND to GND of phone and VCC to VCC it draws 499mA and that sucks...it is really safe to connect D+ and D-?becouse i blow 1 old samsung and nokia n8 xD (ovecloacking wrong polarity and some systeam change (like never turn off))and i dont have any test phone anymore

author: xstream
author_rank: Newbie
timestamp: October 07, 2013, 10:39:43 pm
content: Quote from: Luckymat on October 07, 2013, 07:45:27 pmyesQuoteWell if it is limited it can't draw more and I don't see a reason why it would switch back down. In fact many chargers can only deliver 1A and it works just fine with them.QuoteYes, as long as there isn't anything else connected it is safe. For example if you build a cable that does this and don't use it with a charger but a PC that would not be ideal I think however most systems are protected even in this case. Modifying the power source itself in this way is never a problem.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: October 08, 2013, 12:03:10 am
content: I've collected some info about iPhone/iPad charginghere.The resistor values selected tell the device how much current it may draw.

author: PokemonCookies
author_rank: Newbie
timestamp: October 08, 2013, 05:06:06 am
content: I recently did the same thing, I used a resistor on D+ and on D- I think it was 2 100 ohm resitors and connected them to + and a 5v voltage regulator but for some rason my iPhone says that the device is not compatible.Does anybody know the correct resistor to use?

author: BravoV
author_rank: Super Contributor
timestamp: October 08, 2013, 05:17:02 am
content: Quote from: Jon Chandler on October 08, 2013, 12:03:10 amHey Jon, thanks for pointing that out and also appreciate your works there, since I'm going to build 4 or 5 USB ports charging deck in my car serving various gadgets.Btw, does that resistors configuration works at android device for high current draw ?

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: October 08, 2013, 07:06:39 am
content: The iPhone method isn't compatible with the smart phone method. I don't have a smart phone so I haven't tried this but it might be possible to do both with the two voltage dividers for the iPhone arrangement plus a resistor connected D+ and D–.

author: BravoV
author_rank: Super Contributor
timestamp: October 08, 2013, 07:17:49 am
content: Quote from: Jon Chandler on October 08, 2013, 07:06:39 amIt will be nice if it works for both camps, cause me & wifey own android phone & tablet vs ipad & iphone, and all hell breaks loose in the car when it times for charging those gadgets.

author: Luckymat
author_rank: Contributor
timestamp: October 08, 2013, 07:41:29 am
content: I gonna try it just connecting d+ and d-And i'm not talking about 'I' stuff like IPad or Iphonebut i have2nd questionIf i plug my phone to ac charger with a good quality cable it chargest fastBut uf i connect orginal samsung cable it charges normalSo can i just solder USB port ( Vcc to Vcc ...gnd to gdn and shield ...d+ to d-)And use any cable i want? Like micro usb? Mini usb? Or anything i want?Or need i to cut the high quality cable off and solder it direct?Has anybody any nice ideas? Maybe can somebody send me some photos of their USB charger?

author: zapta
author_rank: Super Contributor
timestamp: October 10, 2013, 05:26:17 am
content: Have you considered buying an off the shelf product? For example this one Link:http://amzn.com/B000N7HT0E(I am sure there are others).(I am using a Galaxy Nexus which allows to change batteries, and carry a spare battery in my wallet. Very small, high energy density and zero conversion losses).

author: Luckymat
author_rank: Contributor
timestamp: October 10, 2013, 08:30:53 am
content: Does it supply at least 1A ? And can 1 power it from 1.2v battery?Becouse my phone needs MUCH power to charge and play HD games in train or on bus station(May be hard to get it if you live in europa (germany))