How do you plug your magsafe? extension cord?

Discussion in 'MacBook Pro' started by ribbon, Mar 18, 2010.

  1. ribbon macrumors member

    Mar 2, 2010
    Just wondering about the differences whether using the extension cord or connecting the transformer directly to the AC. I mean, which one of this two options:

    - macbook ------------[TRANSFORMER]>A/C
    - macbook ------------[TRANSFORMER]------------------>A/C

    Do you understand what I mean? just would like to see if its safier using the second option, or what's the difference.

  2. BlackZ macrumors member


    Mar 29, 2009
    I use macbook ------------[TRANSFORMER]------------------>A/C when i am in the US and the other one when I travel outside US with a different connector.
  3. GGJstudios macrumors Westmere


    May 16, 2008
    There's no preferable method. Both are equally safe.
  4. Intell macrumors P6


    Jan 24, 2010
    I use the little cord wrapped around the brick "wings", with 3 inches loose, then use the A/C cord to plug it into the mains with. It's been that way since day 4 and no problems in eight years of doing it.
  5. m85476585 macrumors 65816

    Feb 26, 2008
    The extension cord is grounded (has a 3-prong plug), which provides a safe path to dissipate static and keeps the computer from having a potential relative to ground. The extension cord also keeps weight off the outlet, which is a bit safer. With the direct plug, the weight of the magsafe could cause it to come out of the socket slightly, exposing energized conductors.

    I have measured 50 volts between my MBP and ground when using the 2-prong adapter. That's not necessarily unsafe since the current is so low, but if part of my body is grounded (feet on a cement floor, for example), I can feel a pulsating electrical sensation as I run my fingers along the aluminum case. With the 3-prong cable I don't feel anything, and the voltage between the case and ground is very close to zero.

    The only time using the 2-prong cable might be better is if you are getting a ground loop. If, for example, you plug your MBP into an audio amplifier that is also grounded, there might be a loud hum or buzz due to a ground loop. In that case, letting either the amplifier or the computer float should eliminate the noise. When I tried to play music in my car with my MBP running off my inverter, I only had the 3-prong cord because I forgot the 2-prong adapter, and there was noise/buzzing. When I ran the MBP on battery power it sounded fine. I assume ungrounding the MBP would have fixed it too, although I wouldn't be surprised if there was still noise using an inverter.
  6. Dooger macrumors 6502

    May 4, 2009
    Sorry to drag up an old thread but I had a (brief) flick through Mroogle and this was the closest thing I could find in the past year.

    I noticed last week that my power brick (15 MBP late 2008) has been making a buzzing sound. Not sure how long it's been doing that for as I usually have my laptop on in noisy environments. I was in a quiet study area and was losing my mind trying to find the source of a quiet buzzing sound when I happened to bring my ear close to the power brick.

    In fairness it is a quiet sound but it got me wondering whether anyone else has had this problem recently and whether it's time to replace the brick?

    Edit: There are three other power bricks in my household (all for 13" MBs and MBPs) and none of them seem to be buzzing.
  7. m85476585 macrumors 65816

    Feb 26, 2008
    Noise from the Magsafe is fairly common. Mine makes sort of a high pitched hissing sound, with a faint buzzing harmonic, especially when it is under heavy load. You could try to get Apple to replace it, but they probably won't. But there's no need to spend any money on a replacement unless it bothers you that much.

    More noise it a compromise Apple had to make to keep the Magsafe small and compact.

    You could try to check the quality of the AC power going into the Magsafe (difficult without specialized equipment*), or try plugging it into another circuit that might have less noise (Reactive loads will generate noise at the wall- things like fridges, air conditioners (large motors in general), fluorescent lights, and cheap switching power supplies are a few examples), but this is not likely to have any effect unless the noise is very bad.

    *In theory, you could measure the power quality with $.50 worth of parts and your MBP's sound card. Simply build a voltage divider with a 4.7K and a 1M resistor to get the output down to ~0.5V, and feed that into the line in of the sound card. Take a short recording, import it into MATLAB, and calculate the THD. Of course I would not want to risk connecting something like that to my computer without better isolation, so use at your own risk.

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