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New 2.1 Amp car USB from TomTom.

Discussion in 'Android Devices' started by rwleigh, May 13, 2011.

  1. rwleigh

    rwleigh Member
    Thread Starter

    I've just seen this new car USB adapter from TomTom and was just wondering if anyone has tried it yet on their desire?

    TomTom High Speed Multi-Charger: Amazon.co.uk: Electronics

    I have the genuine HTC in car adapter which as far as i know can supply 1 Amp, so how fast could you charge using this with the 2.1 Amp socket.

    Cheers,

    Richard...
     



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  2. SiHa

    SiHa Android Enthusiast

    As fast as you could with the 1A one. You can't 'push' extra current into something, the phone regulates how much is taken, not the charger.

    But you could charge two things that need 1A at the same time, which could be kinda handy.
     
  3. rwleigh

    rwleigh Member
    Thread Starter

    I realise what your saying and you're quite right in that the phone takes a current from the supply available but are you sure it's limited to 1A if more is avaialble?
     
  4. SiHa

    SiHa Android Enthusiast

    No that's not how it works I'm afraid.

    The phone takes 1A because the data pins on the charger at shorted to indicate it's a mains charger, not because that's what the charger can supply. If you shorted them together on a cable and plugged it into a USB port on your PC, the phone would pull 1A (and quite possibly fry the motherboard).

    The 2.1A is simply the load that the TomTom can supply without overloading. As I've said, it's just a basic principle of Electronics - it doesn't matter how much current the charger can supply, 1A or 100A, the phone will take 1A.

    In fact, thinking about it, you may have to bodge the TomTom (short the data pins) anyway, just to get the phone to take 1A. Not sure if the cable on the genuine HTC car charger has then shorted of if it's done in the charger as it is with the mains one.

    Think of it this way. The 1A charger will be pulling roughly 450mA from the car battery, but the battery can supply at least 200A. So why doesn't the charger take any more? For the sake of argument I'll ignore the fact that the cigar lighter will be fused at 10-15A...
     
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  5. rwleigh

    rwleigh Member
    Thread Starter

    Thanks for clearing that up, like you say though it might be handy to have two USB ports to charge two devices at 1A...
     
  6. Sak01

    Sak01 Android Expert

    Out of interest, how does the charger make up for the missing 550mA if it only pulls 450mA from the car battery?

    Is it something to do with different voltages? I'll hazard a guess: with the input and output voltage of my car charger being 12V and 5V respectively, input and output power of the charger will be:
    V1 x I1 = V2 x I2
    12 x 450 = 5 x I2
    Therefore, output current of the charger, I2 = 1080mA which will be reduced due to losses to resistance.

    Am I completely on the wrong track?

    ps. I hope no one is offended by the nerdiness on display here lol.
     
  7. SiHa

    SiHa Android Enthusiast

    Absolutely correct, go to the top of the class :D

    The 450mA was only a finger in the air figure, whilst typing.
    Assuming 100% efficiency on the regulator, and using Power = Voltage x Current:
    5V x 1A = 5W
    5W / 12V = 417mA

    But of course there will be losses as you say, so it will probably be around 450 I would think.
     
  8. Sak01

    Sak01 Android Expert

    Woot! I do get a buzz out of successfully applying classroom learning to the real world.

    You must be an electronics engineer or something, right? I only did one module of it back in the day so I'm a novice compared to you.
     
  9. SiHa

    SiHa Android Enthusiast

    Well, I do work in electronics, that's true.
    And I agree, there is something very satisfying about using stuff you learnt at school when you're at work. I was using trig I learnt 25 years ago, last week, to work out the percentage of open space in a staggered grid of punched holes for an airflow simulation.
     
  10. tido88

    tido88 Lurker

    Also recently purchased an ipad charger which also states it delivers 2.1 amps. Is it dangerous to charge the android through a 2.1 amp charger? I understand it won't draw more than it can, but the charger is pushing more amps to it, is it not?

    How would one test the actual amp output of the usb charger using a multimeter?

    Cheers,
     
  11. Harry2

    Harry2 Extreme Android User

    All said in Siha's second post in this thread :)
    So just to round up:

    This 2.1A-charger can't push its 2.1A in a device, the charger is just able to provide devices with up to 2.1A if a device wants to take 2.1A, like an iPad.

    So if a phone wants to be charged with 1A, this 2.1A-charger will charge the phone with 1A.

    Without a multimeter, you might see this with the app 'Battery Monitor Widget'.
    This app will show you how much charging current your phone gets while charging.

    Harry
     
  12. tido88

    tido88 Lurker

    Thanks Harry2, and for the suggestion of the app ill try it. Perhaps the android has some protection, but I've heard other devices can burn up when a higher amp power brick is used by accident. It will make the electronic device run faster than it should, and it will go up in smoke.

    Cheers,

    Edit: I've downloaded the Battery Monitor Widget, and when charging is states.

    Available: 72% +140mA

    Is the 140mA the actual draw?
     
  13. Harry2

    Harry2 Extreme Android User

    Yes, it's your phone's actual draw totally by 72% battery state.

    The charging current is depending on the charging state.
    Current is high with low battery's state, look at the current when your phone has, say 10% battery state.

    Then, when your phone reached 100%, have a look at Battery Monitor Widget's mA by time graph :)

    EDIT:
    Your worry about high amp power:
    Only voltages higher than a device's spec input voltage can burn the device.
    The device determinates the current with its actual resistance.
    In simple terms: This follows Ohm's Law (voltage, resistance, ampere).

    Harry
     

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