Cellphone charger-what makes it different from a power supply? - Page 1
Forum section: electronics / beginners

author: Greate
author_rank: Contributor
timestamp: May 25, 2012, 04:44:23 pm
content: I'm trying to make a portable cellphone charger.I got a circuit from a broken portable psp charger. The circuit still work its just the battries are dead. So what I did was replace the batteries with regular NiMH AA rechargeable baterries. The dead batteries are rated 3.6v so I just connect in series 3 of the regular 1.2v AA NiMH to achive the voltage then parallel 4 of that so I could have more juice. In total that was 12 AA battery. Gpt everything connected, the batteries are chatginggthru that circuit and ot ging an output of 5.07v. I have trie to discharge the batteries on the circuit by driving an electric motor till the battery run out of juice then recharging it once again just to make sure everything works.Now when I connect my cellphone to charge I'm supprized coz it won't charge. I'm sure my connections are correct. My phone (droidx) also chargs from a regular computer usb port which when I measure it only has 5.01v. Another thing I tried is to charggre the phone using my bench top power supply it still did not charge, even I have tried from 4.75v to 6v.Now I think I need some expert advise here.Sent from my A100 using Tapatalk

author: T4P
author_rank: Super Contributor
timestamp: May 25, 2012, 05:00:39 pm
content: 1) Either the charger needs to send a charge signal to the phone (iphone comes to mind)2) Just not enough current, smartphones are pretty fussy about this

author: Greate
author_rank: Contributor
timestamp: May 25, 2012, 06:48:41 pm
content: Anybody can elaborate the charge signal? Does the regular usb from computer sends this signal too? coz my phone charges on regular usb.Having not enough current I assume is out of the issue coz my power supply has an amp meter and can supply up to 1 amp which I think is enough.Sent from my A100 using Tapatalk

author: MikeK
author_rank: Super Contributor
timestamp: May 25, 2012, 07:46:09 pm
content: You can tell if there is a signal being sent to the device if it shows up as hardware. If it's just using the voltage from the USB to power its charging circuit then your computer won't acknowledge it as hardware.

author: T4P
author_rank: Super Contributor
timestamp: May 25, 2012, 07:49:30 pm
content: Quote from: Greate on May 25, 2012, 06:48:41 pmAh yes then your Droid X needs a "activate" signal, my sister had one of the droid (not sure which model but the 8megger version with a bump on the bottom right corner) phones and it wouldn't charge without a signal

author: amyk
author_rank: Super Contributor
timestamp: May 26, 2012, 11:48:11 am
content: The charger detection is implemented using a few resistors or by shorting D- and D+ together in the charger.You can find the full details in the battery charging spechttp://www.usb.org/developers/devclass_docs/BCv1.2_011912.zip

author: SH@RK
author_rank: Contributor
timestamp: May 27, 2012, 02:52:40 am
content: I am no expert but I think this will help.In the end he will make phone chargerAnd I think your current is not enough . Try to find how much normal charger gives .I hope I helpedThanks

author: mariush
author_rank: Super Contributor
timestamp: May 27, 2012, 03:47:00 am
content: As already said, your charger is supposed to have resistors on the d+ and d- lines, which tell the maximum current the charger can give.The phone may see those resistors missing and defaults to minimum current, which is not enough to start charging itself... you have to tell it using those resistors that your charger can give at least 500mA - the default a USB port on the computer offers.Read the pdf that's already provided in this thread, in particular section 3.2Adafruit also has a very nice page about their mintyboost which uses a boost converter to generate 5v from a couple of AA batteries. The page explains in detail how it works and also says the resistor values to "lie" to the phone that it can do more than it actually can (the boost converter can do up to about 600ma as far as I remember but the resistors tell the phone the charger can do 500mA or more all the time).Page is here:http://www.ladyada.net/make/mintyboost/and herehttp://www.ladyada.net/make/mintyboost/process.html

author: kaptain_zero
author_rank: Regular Contributor
timestamp: May 27, 2012, 04:08:01 am
content: As I understand the OP, the device is designed to use a Lithium Polymer cell which has been replaced by NiMH cells. The two chemistries have entirely different requirements for charging. A LiPo only charger cannot understand how to charge NiMH as it is not equipped to monitor for slight drop in peak voltage when the cells are fully charged. The same goes the other way, NiMH/NiCad only chargers cannot charge LiPo cells as they require a very different CC/CV algorithm where charging is halted when the cell drops to only accept 1/10th of the original charge current in the CC portion, when in the CV portion. I suspect the charger control is detecting what it sees as an out of spec battery, perhaps the voltage is simply too low in the discharged NiMH pack, but no matter, the chip will not know when to shut down charging as the current acceptance would not drop as it does in a LiPo. The only hope would be for a timer to shut things down, but I have no idea of what's in the device mentioned.Moral, use a LiPo charger to charge LiPo's. Use a NiMH charger to charge NiMH, and don't mix the two up.RegardsChristian

author: T4P
author_rank: Super Contributor
timestamp: May 27, 2012, 03:28:26 pm
content: Er hey no, it's A lithium ion .

author: kaptain_zero
author_rank: Regular Contributor
timestamp: May 27, 2012, 03:52:55 pm
content: Eh?!?!Quote from: Greate on May 25, 2012, 04:44:23 pm

author: Greate
author_rank: Contributor
timestamp: May 27, 2012, 03:53:33 pm
content: Thanks everyone! I got it working now. Yes the phone needs something on d+ and d-. In my case with the droid x just connecting d+ and d- together is enough to make it use my charger. Now I got a portable charger that I can expand the capacity by adding more AA NiMH to it.Again, thanks!Sent from my A100 using Tapatalk

author: T4P
author_rank: Super Contributor
timestamp: May 27, 2012, 05:59:42 pm
content: Quote from: Greate on May 27, 2012, 03:53:33 pmDafuq ? No you can't use NiMH to it ! Use a whatever brand one hung low and or whatever droid x replacement li-on battery !

author: Greate
author_rank: Contributor
timestamp: June 01, 2012, 11:19:03 pm
content: The NiMH is only used to charge, I'm not powering the droix directly with the NiMH.Sent from my A100 using Tapatalk

author: hlavac
author_rank: Frequent Contributor
timestamp: June 02, 2012, 02:11:54 am
content: Man, disable the tapatalk spam, its extremely annoying.Sent from my Mac using Firefox

author: heychris
author_rank: Contributor
timestamp: June 04, 2012, 09:41:33 am
content: I've been digging into this quite a bit lately. MOstly because I've notice that some 2.1amp chargers charge my droid 4 slower than some 1A. It turns out there is a few standards for phone Identification. Apple does a voltage divider to determine the capabilities of the charger. The USB standards body has one they call BC1.2. There is also the Chinese Telecom Standard. I believe the chinese telecom standard is just shorting the data leads together.I've been trying to figure out what standard my droid uses, but it's still unclear. I have a USB charging cable with built in ammeter/voltmeter I picked up on ebay. I've tried many phone/charger combos. There are a couple key points I've figured out.Charging amperage mostly depends on the phone/deviceCheap cables cause problems. USB.org specifies 28 gauge or thicker. I found several cables with serious resistance/inductance. I believe some cases falsely trigger the voltage divider.There is no consistancy between cost and design of chargers. My best chargers are often the cheapest.Almost all car chargers have only a voltage regulator and a voltage divider for detection.Texas instruments publishes a Design Reference for an AC and Car phone charger. Often they'll publish Gerber files for the TI design reference boards. I haven't found the current version and am designing my own version.http://www.ti.com/tool/pmp5951http://www.ti.com/tool/pmp5952