Charging: USB and AC differences


  1. Newth

    Newth Well-Known Member

    I know this is stating the obvious, so what have I missed.

    A normal USB socket on a PC is rated at 500mA. A phone, or any other device, plugged into this shouldn't pull more than 500mA or it risks damaging the PC. Surely this means that the manufacturers of the car chargers are latching onto this & using this over current protection, to stop there 5p voltage regulator from being melted. If you short out the pins & take away this protection, the poor little cig charger is going to give up very quickly, as it's not meant to cope with the sort of current that will be demanded.
    baldmosher likes this.
  2. jabtas

    jabtas Well-Known Member

    The problem is occurring with 500ma being not enough to power the phone while it is running several app
    People are running satnav, gps, plus others and a standard 500ma just cannot keep up so even the phone is plugged into a power supply its still discharging the battery
  3. marshalex

    marshalex Well-Known Member

    ebay, belkin verified the serial number when going through their chat system yesterday so thats not a problem. didn't help that the person i was speaking to didn't quite understand the concept of quick charge and the output it was supposed to supply!
  4. Newth

    Newth Well-Known Member


    Sorry, Don't think I explained my post to well. I understand what people are trying to do, I don't understand why they they are trying to make a charger do more than it should.

    Is it because of using a 'data' usb lead, instead of a 'charge' usb lead?
  5. sandozer

    sandozer Well-Known Member

    OK here is the situation, I am using the USB adapter in the car, engine not running.

    Case one. My 5 year old Belkin 12 USB adapter, rated at 700ma, part no USB-CLA, 10R-021626. input 12-24Vdc.

    As connected to the Desire it delivers 400ma, linking the Data connections, it delivers 700ma. This adapter puts out 5.5V (this data shorting condition is done to automatically charge at a higher rate, detected by the battery manager in the HTC battery).

    The BAD news, I bought a new Belkin 12V USB adapter, rated at 1AMP, part no F8Z445ea, #8830-00800ea. This one delivers 400ma, linking the Data connections it delivers 530ma. This adapter puts out 5.2V.

    Obviously the current switching trick is something HTC know about, and Belkin dont. So dont put your faith in new USB adapters delivering what you are hoping for! It also explains how the AC charger charges at the higher rate, do a resistance check on the data lines in the AC charger, they are shorted.

    I did these tests using a split USB lead and a Fluke DMM, I cannot see how the lead can make any difference in charging. There are 4 wires, two power, two data and a common screen to the outers. It is a one to one connection, no black magic. Anything different you may just have a faulty cable.

    If anyone comes up with an adapter that can deliver more than 700ma, in the car, please let me know. :cool:
  6. marshalex

    marshalex Well-Known Member

    i can confirm that as belkin didn't seem to know anything about it and kept trying to fob it off as cable/phone problems. after much perseverance belkin have acknowledged that there may be a problem with the adaptor not using the quick charge which they will have to pass on. unfortunately now this leaves me stuck without a charger that i can use in the car to power the handset. anyone know if the htc car charging kit is the same? need to work out now whether to send it back or not.
  7. sandozer

    sandozer Well-Known Member


    That is a good call, anyone know if HTC`s USB car adapter has the shorted data lines? Its a really easy check to do guys!!
  8. brunop

    brunop Member

    Ok, I shorted the data pins on this charger yesterday

    Micro DC to USB Adaptor : Caravan & Camping : Maplin

    and am happy to report the phone detects AC charge, and it supplies enough current to charge the phone whilst using bluetooth, navigation and phone calls. I used the HTC supplied USB cable with it.

    Unfortunately I don't have a means of testing the actual output or the voltage with this mod in place, but it appears to do the trick and both charger and phone don't appear to be getting too hot.

    hope this helps, obviously I accept no responsibilty for any damage caused!
  9. Newth

    Newth Well-Known Member

    Not sure if this helps anyone & there's a strong chance I have it wrong of course.

    From what I understand, the USB lead doesn't have the data wires tagged together.
    This means that if you put the lead into a charger, be it AC or DC, it will only charger at the lower rate of 500mA, as the Desire will treat it as a PC connection.
    This is overcome by the Desire's AC charger having the data wires joined internally, so it doesn't matter that the USB lead doesn't.

    You too can easily overcome this problem for your car charger by getting another lead & shorting together the data wires. However, if you then use this lead on your PC, the phone may damage your PC, if it's 5V rail is weak. (500mA max for USB remember & the phone may well try to take more). Other than that, the lead obviously won't connect.

    Finally, don't take the ratings very seriously on these things. I would imagine the 1A charger mentioned above can't do 1A for long, if at all. By shorting the data wires together, you may well end it's days quickly. Again, this depends on the regulation circuit built into it.

    A better test (if someone could be arsed) would be to study the charging current over a fully charging cycle.
    Let the battery go flat, then charge the phone whilst not using it.
    Then a second test, same flat battery, but use the phone & see what current it draws.
    Both these would need to be done on the mains charger.
    Third & forth, run the tests again, but using a car charger. I bet the current is less, even with the belkin 1A unit.
    If you really wanted to push the boat out, run a fifth test with 5V PSU that is 'really' rated at over 2A. See what current the phone pulls then.
    You may find that over the charging cycle, the current demand changes. It all depends how clever the Desire is I suppose.

    Sorry for the long post, think I got carried away!
  10. shmicky

    shmicky Member

    Apart from time taken, does it make any difference whether you charge it @ 500mA, 700mA, or 1A ?
    Will it damage the battery ? I assume it wont ?
  11. brunop

    brunop Member

    I'm pretty sure the phone actually controls how much current it draws from the charger, so just becuase a charger is rated at say 2A, it doesn't actually output that constantly, thats just what it is capable of supplying.

    So in answer to your question, no it won't damage the battery.

    If you plugged in something that was a higher voltage, now that would almost certainly cause some damage.
  12. iynCognito

    iynCognito Well-Known Member


    I do believe its actually the data lines on the CHARGER that need to be shorted. THe USB cable can be the same whether for a true AC wall charger or a USB car charger.

    Just as sandozer is asking, does anyone have a car usb charger that reads as "AC charging" on the phone / battery when plugged in?
  13. hainman

    hainman Well-Known Member

    hi guys.kinda following the jist of the conversation,can i ask if its safe to use wall charger for n97,seems to be same micro charger as desire,also my wife had a small extention for attaching to a normal nokia charger in the event that the main one got lost or broke,i have attached it to a cigarette lighter charger and it seems to charge it ok but is it going to damage my desire battery??i dont know wat what power its ommitting,not that clued up on wattage and power output!!
  14. hainman

    hainman Well-Known Member

    hi guys,as i stated in my post i took my wifes wee mini charger addaptor for hr n97 which you can connect to any newish or old nokia charger and charge your handset,i just went to my car and plugged it into cagarette lighter and connected it up to my desire,went to settings;battery; and it said "charging ac" hope this helps anyone,if i knew how to upload a pic i would to show what im using and my findings,:D
  15. shmicky

    shmicky Member

    From my investigations only a HTC CHARGER gives the Charging AC message on the phone - which I assume means 1A.

    My ipod USB charger which is 5v/1A, with both a normal USB lead, and the HTC supplied lead, still says CHARGING USB.
    Just the HTC Charger seems to supply 1A..
    I bought a Belkin Micro Car charger whose output is 5v/1A, but even with that it still says charging USB..

    strange.
  16. hainman

    hainman Well-Known Member

    maybe the nokia charger addaptor is differant than a normal incar charger,i can assure you it says CHARGING AC,if i knew how to put pic up i would kindly show you what the status says and what the charger is im using!:cool:
  17. sandozer

    sandozer Well-Known Member

    This is so SIMPLE......

    To get the HI charge rate in the car,

    AC, 1AMP, whatever you want to call it then the DATA LINES MUST BE SHORTED AT THE USB CHARGER SOCKET !!!!! The AC charging will be indicated on the phone.

    I get the feeling I am repeating this post somewhat. :rolleyes:
    baldmosher likes this.
  18. shmicky

    shmicky Member

    Is that the two centre contacts that need to be shorted ?
  19. hainman

    hainman Well-Known Member

    the thing is i havent modified anything all im using is a nokia mini usb charger adapter that plugs into an in-car charger.no shorting any wires or anything
  20. sandozer

    sandozer Well-Known Member

    If you are getting the CHARGING AC indicated then the data lines must be shorted to tell the battery to go to the Hi-charge mode, think yourself lucky that it does !!
  21. sandozer

    sandozer Well-Known Member

    Correct, at the USB charger socket end....
  22. hainman

    hainman Well-Known Member

    well it must have came that way i havnt touched anything,its just a stock standard in-car charger for a nokia plus the mini adapter charger that came with my wifes n97.if its something thats gona benifit me then i cant complain but its also something for people to look into if it can help some1 else acheive better charging in-car!
  23. marshalex

    marshalex Well-Known Member

    i'm assuming you mean the htc car charger pack?
  24. jimdriver2

    jimdriver2 Well-Known Member

    Sorry that's not correct. I used a tried my really basic car charger (bought for
  25. iynCognito

    iynCognito Well-Known Member

    Very interesting! I just want to check. When you say a "standard in-car charger for a Nokia", what kind of end does it have? A mini-USB (like those on a digital camera), or a round Nokia small like this

    Nokia DC-4 - In car charger: Amazon.co.uk: Electronics & Photo

    or a round Nokia large like this

    Nokia LCH-12 Car Charger: Amazon.co.uk: Electronics & Photo

    and then use an adaptor like this

    U-Bop Nokia 3.5mm Large Pin to Nokia Micro USB Charging: Amazon.co.uk: Electronics & Photo

    If that is the case, then the adaptor / Nokia charger combo must look like a "shorted" micro USB to the phone and voila! I may hunt one down then!

    (Sorry sandozer, it would likely be a disaster if I try to open up and short my usb car charger!)

Share This Page