New 12" rMB Charging with an External Power Bank

Discussion in 'MacBook' started by mafaky, Sep 8, 2015.

  1. mafaky macrumors regular

    mafaky

    Joined:
    Jun 12, 2014
    Location:
    Istanbul, Turkey
    #1
    Hi folks. This case may have been mentioned/discussed previously in other threads related to the new slim and feather light 12" rMB. My apologies, if this is repetition!...

    I recently came over a review posted sometime in May this year. The reviewer was claiming that he managed o charge the 12" rMB (while in "off" or "sleep" mode, only) with the 2.1A (or maybe 2.4A) output of the the standard 5.0Vdc output of an external (portable) hi-capacity power bank. He concluded, it took much longer to complete a charge cycle: like 5-6 hrs.

    I addressed him privately and he re-confirmed the case and added he also tried with several other power banks. But he failed to give the technical explanation as how it was possible to charge his laptop (which normally is charged with 14.0Vdc @ 2.0A) only with a regulated (fixed/stable) 5.0Vdc source (the power bank's output).

    An explanation came from another guy, indicating that there "should be" a SEPIC topology converter in the laptop which actually converts the 5.0Vdc input to a higher voltage (possibly 15.0Vdc).

    This explanation sounds "reasonable"; yes there are such ICs custom built for the said voltage multiplication, battery monitoring, etc. But I'm not 100% sure if there's one of these ICs inside the mentioned Apple laptop...???

    But still I cannot fully dig out why Apple (if, yes) has opted this circuitry: what's the big idea behind charging the laptop while it's only inoperative and at a very slow rate than the normal? :confused:

    Any ideas or comments, mostly welcomed...
     
  2. Tummy, Sep 9, 2015
    Last edited: Sep 9, 2015

    Tummy macrumors regular

    Joined:
    Feb 1, 2008
    #2
    The battery can only typically output 5v at ~2.1 amps (10.5 watts up to 12 watts). I noticed that my computer uses uses about 5-12 watts while it's running. So you would only be able to charge with the excess watts.
     
  3. mafaky thread starter macrumors regular

    mafaky

    Joined:
    Jun 12, 2014
    Location:
    Istanbul, Turkey
    #3
    The "watts" (or the power) supplied and consumed are only part of the factors that are involved, but not all. Here we have a source that can supply only 5Vdc (the external power bank..). Forget about its output current capavity. On the other hand we have a load (the 12" rMB) that needs to be charged at 14.5Vdc. Also forget about its current requirement.

    Now, if some precautions are to be taken, a 14.5Vdc source can/may charge a 5Vdc load but can you technically explain as how a 5Vdc source can charge a 14.5Vdc load?:confused:
     
  4. xPad macrumors regular

    Joined:
    Dec 15, 2013
    #4
    The port isn't a DC port, it's a digital port, which can reconfigure itself to operate in many different modes. It's designed into the USB 3.1 spec.
     
  5. mafaky thread starter macrumors regular

    mafaky

    Joined:
    Jun 12, 2014
    Location:
    Istanbul, Turkey
    #5
    I know that is not a standard DC port, but are you telling that once you input 5.0Vdc to the USB-C (USB3.1) port, the output is somehow increased to 14.5Vdc? Can you give a more specific link, describing this process???
     
  6. Tummy macrumors regular

    Joined:
    Feb 1, 2008
    #6
    I don't know how to explain it more clearly, I'm a designer not an electrical engineer. Maybe it's a language thing but you sound kind of pedantic. If you don't understand then just believe in "Apple Magic" that it just works.
     
  7. Queen6, Sep 10, 2015
    Last edited: Sep 10, 2015

    Queen6 macrumors 603

    Queen6

    Joined:
    Dec 11, 2008
    Location:
    Enjoying Better Things
    #7
    It clearly explained in the USB C standards, power supply, voltage and current is negotiated between devices on connection, nor is it relevant for the majority of users;
    Screen Shot 2015-09-10 at 19.48.23.png
    5V is the USB default that must be supported to provide interoperability with existing Devices. However, higher voltages are needed to provide more power through USB connectors because of their current carrying capability.

    12V was selected because it is very common in PCs and many other systems. The curre nt limitation of the Micro USB Connector family is 3A for the enhanced PD version. The use of 12V with 3A provides sufficient power to charge tablets in the 20-30W range that use the Micro USB Connector.

    20V was selected because larger systems, such as notebooks, often have 4 lithium cells in series and require charging voltages in the 18-20V range. A sampling of systems showed that chargers for these systems were typically 19.5-20V. Typical systems had chargers that supplied between 60W and 100W with the exception of a few very high-end performance systems that were well over 100W. The 5A current limit of the PD enhanced Standard -A and Standard-B connectors, with 20V allows up to 100W to be delivered to charge this class of Devices.

    For those that want to know the exact mechanism, you will need some formal education/training on electronics, IC`s & software control. It also entails a fair amount of reading across multiple documents.

    http://www.usb.org/developers/docs

    Q-6
     

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