USB-C charging cable with LED indicator

Discussion in 'MacBook Pro' started by TibookAktive, Dec 2, 2016.

  1. TibookAktive macrumors member

    Joined:
    May 27, 2010
    #1
    Quick question for hopefully the electrical engineers that frequent this forum.

    I have the new 2016 15" MBP & really miss the charging indicator light (orange when charging, green when full). I have found a Moshi USB-C charging cable that has this feature:

    https://www.moshi.com/usb-c-charge-cable#white

    My question is that the cable is only rated for 60W. It is listed as compatible with the new 15" MBP, so I'm not concerned about safety, but I wanted to ask someone with an electrical engineering background what would actually happen when using the Apple 87W charger?

    Does the charger somehow detect that the cable is only 60W rated and downgrade its delivery? Does it try and supply as much as possible and detects it can only send ~60W before being unsafe? Or is this one of those times where it's only rated to 60W, but in reality 87W is not much more and although the manaufacurer wont say it supports this, in reality the full 87W will be able to be sent?

    Really want to get this cable, but concerned going to lose 25% in charging speed.

    Any advice would be helpful.

    Thanks
     
  2. macintoshmac macrumors 68030

    macintoshmac

    Joined:
    May 13, 2010
    #2
    And, what about using this cable with the 61w charger Apple supplies with the 13?
     
  3. TibookAktive thread starter macrumors member

    Joined:
    May 27, 2010
    #3
    Guess it would work fine with the 13" charger, as perfectly rated for that. My point was more that I want to keep the full 87W charging ability of the current 15" charger - so just wanted to get a feel for what would happen from a technical electrical perspective when an 87W charger is used with a 60W rated cable.

    If the upshot is that the charger would downgrade to 60W and only supply that, then I'll probably pass, as don't want my charging time to be severely increased for the sake of having an LED on the cable :)

    But if the consensus is that although cable rated 60W, 87W (or close to) would still get sent as there are wide tolerances - then I may give it a go.

    Hope this makes sense.

    Thks
     
  4. macintoshmac macrumors 68030

    macintoshmac

    Joined:
    May 13, 2010
    #4
    Write to Moshi about it, too. Nothing better than information straight from the horse's mouth.
     
  5. TibookAktive thread starter macrumors member

    Joined:
    May 27, 2010
    #5
    I did actually already speak to them... Their response:

    "While our USB-C Charge Cable is compatible with the new MacBook Pro 15", this cable only supports 60W. While you may experience slowing charging compared to the included Apple charger + cable, our production team has not yet finished all their charging tests at this time"

    So as highlighted this seems to confirm it will work safely and highlight the fact it may charge slower but still running their tests. I was just wondering if anyone with knowledge of the type of electronics involved here, what the likely outcome will be of using a "rated 60W" cable with an 87W Apple charger?

    Thks
     
  6. steve-p macrumors 68000

    steve-p

    Joined:
    Oct 14, 2008
    Location:
    Newbury, UK
    #6
    One likely outcome is that not only would it charge more slowly, but the battery will get slowly depleted if you are doing things that use a lot of power, like sustained maximum CPU. It won't be able meet the power requirement from the charger alone.
     
  7. chriscrowlee macrumors 65816

    chriscrowlee

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    Aug 10, 2015
    Location:
    San Diego, CA
    #7
    How does the cable know when the laptop isn't accepting any charge anymore? My understanding is the cable just supplies power, and in the Lightning cables Apple had a chip inside that communicated with the laptop. They don't have that sort of thing for USB C in my understanding
     
  8. thesaint024 macrumors 65816

    thesaint024

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    Location:
    suspension waiting room
    #8
    Typical CYA response from manufacturer. I would have guessed that verbatim. Nice find though! The charging light is the only thing I missed about magsafe. I would jump at a cable that did that and had full usb-c data transfer speed. It would be nice to have more flexible functionality from a usb-c cable than just charging if I'm going to carry it around. Wishful thinking? Too much to ask for the usb-c utopia?
     
  9. elf69 macrumors 68020

    elf69

    Joined:
    Jun 2, 2016
    Location:
    Cornwall UK
    #9
    from what i read about the older magesafe laptops apple has battery cutoff built in to stop battery over charging.

    so if this is true of the type C laptops then the laptop would stop drawing as much power from charger so if cable can detect this then can change led colour.

    my magsafe get warm when charging laptop but once charged cools down even when still connected to laptop.
     
  10. poorcody macrumors 6502a

    poorcody

    Joined:
    Jul 23, 2013
    #10
    Generally USB-C cables rated for 60w have an electrical resistor in them. The resister simply prevents too much power from flowing through. So if your charger tries to push 87w, it will only allow 60w through. (Think of an electrical resistor as the knob on your faucet that you can turn to adjust the amount of water flow.)

    Many USB-C cables have this to protect equipment not designed for the new higher wattages allowed in USB-C.

    If you're worried about 60watts being too limiting, realize you are still getting ~69% of the power at this rate. My 15" Pro takes about 75 minutes to charge from zero: that would mean it would take about 110 minutes (an extra 35 minutes) at 60w. Not too big a deal.

    In terms of usage, you will rarely draw 60watts while running (I typically draw 5-12 watts according to Coconut Battery). You'd have to have all 4 cores running full speed, dGPU on, etc. And even when that happens, it rarely does so for a sustained period of time.

    TL;DR: 60w cable is safe and will probably cause little loss of convenience.
     
  11. anson42 macrumors 6502

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    Mar 13, 2014
    Location:
    Oakland, CA
    #11
    I don't think they know. My guess is as long as there is power present in the cable the LED is lit, more of a good connection indicator rather than the charge indicator we're used to.
     
  12. chriscrowlee macrumors 65816

    chriscrowlee

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    Aug 10, 2015
    Location:
    San Diego, CA
    #12
    Well if you go to that website linked above, the product info shows a orange light, and then a green light, so it's either false advertising, otherwise I can't explain what orange vs green would indicate.

    I'd love to hear from someone who has the cable to get some feedback as to how it works.
     
  13. anson42 macrumors 6502

    Joined:
    Mar 13, 2014
    Location:
    Oakland, CA
    #13
    Hmm, interesting. The indicator must be reflecting a level of power draw through the cable. A higher power draw from a charging computer yields the orange light and a green light to reflect low to no power draw. Hope they're working on a higher wattage version of the cable for us MBP owners.
     
  14. tengda macrumors newbie

    Joined:
    Dec 2, 2016
    #14
    is charing 15" with the 12" MacBook's power brick harmful to the 15" MBP tb?
    --- Post Merged, Dec 3, 2016 ---
    is charing 15" with the 12" MacBook's power brick harmful to the 15" MBP tb? thanks
     
  15. TibookAktive thread starter macrumors member

    Joined:
    May 27, 2010
    #15
    Thanks for the response! This is exactly what I was looking for - I knew there would be an electrical engineer (or at very least knowledgable hobbyist) to come with the answer!

    I really do miss the charging indicator on my cable, so might take the slightly longer charging time to get the functionality. As noted above it does seem to be orange when charging and then change to green when full, so that's good. Maybe I should wait and see if they launch a 90W rated cable for the 15" :)
     

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