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Thread: USB charging

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    USB charging

    Hey all

    As some of you who have the new Coby gen3 tablets will have noticed; these tablets support charging through the USB port.

    However, you may not have realised that charging through the USB port is not as fast as using the mains adaptor. After checking the estimated charging time with my 9742 connected to USB and then the mains adaptor, I found that the charge time was roughly double for USB charging.

    I also found that having the USB cable connected to a 1A adaptor while the mains charger was plugged in also did not affect charging time.

    Based on this I think we can safely assume that these tablets (at least some of the gen3) have a proper charging circuit with current limiting (at least on the USB port, I tried an iPad charger as well) that suggests to me that we can safely use mains adaptors with higher current ratings than standard.

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    the more amperage you provide the faster it will charge
    its just a limitation of usb though
    Last edited by Joe88; 06-03-2012 at 04:10 AM.

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    Quote Originally Posted by Joe88 View Post
    the more amperage you provide the faster it will charge
    its just a limitation of usb though
    Actually, I've tested this fairly thoroughly. A 2A mains USB charger is giving the same charging time as a 1A mains USB charger.

    This means the current is being limited by the tablet; if it wasn't there would be a difference in the charging times.

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    Are you suggesting that the software controls the speed at which the tablet charges via USB? Or is this determined via hardware? If via software we could possibly change this setting.

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    Quote Originally Posted by vampirefo. View Post
    Are you suggesting that the software controls the speed at which the tablet charges via USB? Or is this determined via hardware? If via software we could possibly change this setting.
    I suspect we have a piece of hardware (e.g. a FET of some kind) controlling the amount of current going through the USB port. I've started using a home-made USB-DC charging cable and I've found that there is a significant difference in the charging rate between this and the standard mini-USB cable off the same powered hub.

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    The amount of charge you will get coming from say a computer usb port, and that of a ac dc adapter charger is going to be much different. I have a NiMH battery recharger and on it is also a usb port to charge devices. Since its never going to host a device, just charge one (or possibly multiple with a daisy chain) it kicks out more juice, and therefore charges my tablet quick then say hooking it up to my desktop. Is this what your talking about? Other then that there is a limit on the amount a usb port can take and therefore pass it on to the battery. The leads between the dc charger and the battery are thicker, and can handle more.

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    Quote Originally Posted by ziggyzag View Post
    The amount of charge you will get coming from say a computer usb port, and that of a ac dc adapter charger is going to be much different. I have a NiMH battery recharger and on it is also a usb port to charge devices. Since its never going to host a device, just charge one (or possibly multiple with a daisy chain) it kicks out more juice, and therefore charges my tablet quick then say hooking it up to my desktop. Is this what your talking about? Other then that there is a limit on the amount a usb port can take and therefore pass it on to the battery. The leads between the dc charger and the battery are thicker, and can handle more.
    You need to look at the current output that specific USB port is capable of providing; the original USB standard (1.0/1.1/2.0) is for 500mA (900mA for USB 3.0).

    However with devices like the iPad and Galaxy Tab charging from USB, it is not uncommon to see USB ports capable of providing current up to 2.1A.
    Additionally, when using a device such as a powered USB hub, it is common to be able to draw up to the full current rating of the connected power supply.


    TLDR version: Charging off a USB port is limited by:

    1. How much current (Amps or mA) the USB port can provide.
    2. The maximum charging rate of the device.

    The point I was trying to make before, was that while these tablets can charge off of USB there seems to be something in the circuitry which limits the charging rate through the USB port that is not present on the DC socket.

    As far as how fast your battery charger can charge a tablet, look for an mA rating for the USB port, I'm guessing it will be either 1A or 500mA. At this level of current wire thickness is more about durability than current capacity.

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    Quote Originally Posted by subtotal View Post
    As some of you who have the new Coby gen3 tablets will have noticed; these tablets support charging through the USB port.
    I was going to ask this exact question for other tablet manufacturers, and looks like I got my answer here for the Coby!

    Does Android indicate the status as "Charging" when you charge via USB?

    See results for my tablet here: Charging tablet via USB

    Some manufacturers log the charging current in the Android logcat: see http://www.droidforums.net/forum/sho....php?p=1312534 for the Motorola DroidX Smartphone.
    Last edited by Natey2; 06-15-2012 at 07:23 AM.

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    When connected to USB the battery icon on the status bar shows the 'charging' animation.

    Also for the record, I used the app ZDbox (needs to be sideloaded but works fine) to gauge charging rate through charge time.
    If anyone knows of an app that displays charge current, let me know and I will repeat the experiment using that.

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    help:)

    my android tablet, (arnova 7G2) will not charge. is there any other way to charge it apart from using the main charger???


 
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