Using self-made Magsafe possible?

Discussion in 'MacBook Pro' started by fl89, Sep 1, 2012.

  1. fl89 macrumors newbie


    Jan 24, 2011
    afaik, the Magsafe 85W has a voltage of 18,5V.

    So if I buy an 18,5v supply and put a magsafe connector on it, there would be no problems right?

    I'm asking because the macbook pro changes voltage on demand. When charging, on idle.... is the power adaptor doing that or a converter on the logic board inside the mbp? :confused:
  2. charlieegan3 macrumors 68020


    Feb 16, 2012
    This sounds kind of dodgy, why can't you get a new one?
  3. fl89, Sep 1, 2012
    Last edited: Sep 1, 2012

    fl89 thread starter macrumors newbie


    Jan 24, 2011
    Cause I like doing this stuff...strange for a mac user right? :D (using linux/windows too)

    And the magsafe it too pricey and has not enough power...draining battery when converting/processing videos.

    So, do I miss something? :confused:
  4. stuaz macrumors 6502

    Jun 16, 2012
    Sounds like something not to fool around with - could be a potential fire risk if you mess with the electricity like that.
  5. Mabyboi macrumors 6502


    Apr 23, 2010
    Ontario, Canada
    Don't try it, too many things can go wrong, a new MagSafe is only $80 anyways...
  6. chibisukee macrumors newbie

    Jun 23, 2012
    Magsafe has a charge control pin (the middle one) that sends information between the charger and the laptop - I don't think that you can just connect the Magsafe connector to any power adapter.

    And where would you get a Magsafe connector without the actual power adapter? I thought Apple has issues with people manufacturing their own Magsafe connectors.
  7. gentlefury macrumors 68030

    Jul 21, 2011
    Los Angeles, CA
    Not sure that calling the users of this forum stupid is the best way to get help.
  8. quasinormal macrumors 6502a

    Oct 26, 2007
    Sydney, Australia.
    I'm not entirely sure about that. I've only ever seen two wires on the dc end of MagSafe cable.

    I don't think it would be a problem if the power quality from tranformer is adequate. I've used a few 3rd party dc adapters and the Hypermac battery pack without any obvious issues over the last 5 years.
  9. fl89, Sep 1, 2012
    Last edited: Sep 1, 2012

    fl89 thread starter macrumors newbie


    Jan 24, 2011
    1. Are you sure? So how can these guys do it?

    Look here: Magsafe do it yourself

    From Wikipedia
    2. The magsafe connector is from an old, damaged magsafe.

    Hold on, never said that. It was just a joke, because he asked me what the point of doing this was. ok? ;)

    So can someone tell me why this should not work? For example, this one is selling parts for building your own adapter.

    Oh wow, thanks buddy. Finally someone having a point and not just tellin me that it could be a problem without a reason :rolleyes:

    So the macbook is regulating the voltage on the inside, right? ...maybe i will try to measure the output of the magsafe, its just hard to bridge the dock connector without cutting the wire :(
  10. NutsNGum macrumors 68030


    Jul 30, 2010
    Glasgow, Scotland
  11. Dark Void macrumors 68030

    Dark Void

    Jun 1, 2011
    I would stay away from this whether it's possible or not, does not seem worth it and even more so if something goes wrong you'll end up setting yourself way back in comparison to just purchasing a new magsafe charger.
  12. fl89 thread starter macrumors newbie


    Jan 24, 2011
  13. alphaod macrumors Core


    Feb 9, 2008
    If you're asking, you're not qualified. I do a lot DIY stuff and I don't go onto some random forum asking people if it's possible; even I'm not very qualified. I've fried a lot of stuff, including myself.

    In answering your question, the MagSafe charger is self sensing. Assuming you have the 85W adapter, it can provide 45W, 60W, or 85W based on if you have a MacBook Air, 13" MacBook [Pro], or a 15" and 17" MacBook Pro, respectively.
  14. fl89 thread starter macrumors newbie


    Jan 24, 2011
    Thank you. Great links. So there is no extra cable inside. Only +VDC and ground.

    Now I just need to find out if the 6,86V with no load are produced inside the magsafe or the magsafe-connector. Will measure that when my multimeter arrives.

    If the magsafe-connector does all the work, my problem is solved. :cool:

    In the end its so easy. Even for someone who is not an Electrical engineer.
  15. alphaod macrumors Core


    Feb 9, 2008
    Good luck!
  16. avalys macrumors 6502

    Jun 4, 2004
    Nitpick: this is not some unique or special property of Apple power supplies. All power supplies can be used at or below their maximum rated power (e.g. an 85W power supply can provide any power from 0W-85W), as long as the voltage is correct. The reason Apple's power supplies are interchangeable is that they all provide the same voltage.

    Additionally, the numbers you listed (45W, 60W, 85W) are simply the maximum ratings of the power supplies Apple shipped with each computer. That doesn't mean the MBA uses 45W, and the MacBook Pro draws 85W. It all depends on load. You can power a MacBook Pro perfectly adequately on a 45W power supply, as long as the battery is charged and you're not doing anything CPU/GPU-intensitve.
  17. fl89, Sep 1, 2012
    Last edited: Sep 1, 2012

    fl89 thread starter macrumors newbie


    Jan 24, 2011
    Thank you. I know it's not that easy. But maybe I'm really that lucky and everything works just fine. :D

    Yes, but only the 85w supply can provide a higher voltage 18,5V than the others 16,5.

    I found this quite useful information. It's about what output voltage you should use on the universal power adapter they sell. Q&A

    In my case I would choose N3(B) tip with 18,5V. :D

    Here's some more information on how the magsafe works.

    Stanford Magsafe

    Hmmm, the voltage switching is kind of weird. But 18,5V should work nonetheless.
    I'm trying to contact that guy, maybe he knows more since he sells adapters like that.
  18. n748 macrumors newbie


    Jun 19, 2010
    Hey fl89

    Great thread - thank you. I was a bit surprised about the discouraging feedback you received in the beginning.

    It has been one year since your last post and I was wondering if you could give a short follow-up. I would like to do something similar: Power my MBP from a 12V solar-charged lead acid battery. The most efficient way is to get good components and start soldering, it seems.

    I would be especially curious if 18.5V turned out the right option or is the 16.5V (60W) option more suitable? As far as I understood, the power rating is programmed into the cable (not the power supply - cf. here). So what happens if I only can find a 60W-rated cable and turn the voltage to 18.5V. After reading all of your links and some more, it seems to be more reasonable to go 16.5V and accept a battery drain when playing the latest shooter games ;)
  19. Swampus macrumors 6502


    Jun 20, 2013
    Before you build something to step the voltage up and provide some in-line protection, the most "efficient" way might be to simply spend $30 on a car adapter? Something like this?

    Solar panel --> charge controller --> battery --> car adapter --> MBP.
  20. magbarn macrumors 68000

    Oct 25, 2008
    Yup, this is what I'm doing. I have the solar panel charging via a charge controller a 12v deep cycle which is then wired to a 150 watt 120V AC inverter which then my regular magsafe power adapter is plugged into.

    I also fly RC helis and I've converted a few of my lipo battery packs to 4S which gives around 16 volts which is perfect for a magsafe connector like the ones from macgyver.
  21. g4cube macrumors 6502a

    Apr 22, 2003
    Great thread and links.

    I too was planning to tinker to build a mobile setup powered by the more common +12v from vehicles and standby battery packs used to start cars when their battery is dead.

    1. refurb working Apple official adapters are available at OWC for $45-55 according to an email I got today
    2. I had planned to use a DC-to-DC converter to step up the nominal +12v to nominal +18v (for example, the airline adapter Apple sells will power but not charge a laptop due to voltage being only +15v - EmPower)
    3. lots of "broken" adapters on ebay to scavenge for official MagSafe connectors

    Why? More efficient and less bulky than using +12vdc to 120vac converters and then using the Apple laptop chargers. Also, many hard drives use simple +12vdc power, so was planning to generate regulated +12vdc from the battery source.

    Finally, investigated some lithium power packs if car battery power not available. Then would have to also worry about charging circuitry.

    Overall, an interesting project.
  22. Freddruppel macrumors newbie

    Jul 17, 2016
    Just reviving the thread here ^^ (it might be useful for someone !)

    My MagSafe transformer died after 4 weeks of use (it was a chinese knockoff I found on eBay for ~20)
    As I didn't want to borrow my mom's charger for too long, I decided to try and make a new charger. So I salvaged the MagSafe cable (and other components for other projects ^^) from my charger, and hooked it up to a DC-DC boost converter (you can find those on eBay relatively cheaply). I used a basic 12V transformer as power source, and after many verifications of the output voltage (18V instead of 18.5V, just to be sure), I took a deep breath and plugged the cable into my MacBook, and it worked just fine !!

    Although it's not really recommended, it works as a "short-time" solution, as I don't have the time and money now to buy a genuine one..

    Hope this helps !!
  23. jerryk macrumors 601

    Nov 3, 2011
    SF Bay Area
    I use this one for my MacBook Pro. Works well and is cheap.
  24. Elcapacito1919 macrumors newbie

    Jul 16, 2016
    I don't think he call anyone stupid..... did you heard him say that???

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