power draw on mac magsafe cord,battery and perihperals

Discussion in 'MacBook Pro' started by Sossity, Mar 20, 2011.

  1. Sossity macrumors 65816

    May 12, 2010
    I read and learned from here that the current 85watt magsafe AC cords that come with macbook pros may not provide enough power, & when plugged in & with the mac under heavy load may still dip into the battery reserves.

    would an external hard drive plugged into the mac via firewire or usb with an AC cord that also may not provide enough power to the hard drive make an additional draw on the mac?

    i read that some enclosures do not & someone had actually bought a 6 volt monitor power cord to use on their hard drive enclosure, I think this was about earlier versions of the macally enclosures.

    how can I be sure my enclosure's power cords are providing enough power to my hard drives? & in turn avoid drawing too much power from my laptop?
  2. grahamnp macrumors 6502a

    Jun 4, 2008
    I have never encountered a situation where a mains powered external drive was not sufficiently powered by the included wall wart. Outside of Apple, the tech industry tends to overbuild these things.

    Only 2.5" drives should be sucking up bus power. I've tried running multiple 3.5" external drives all through the same unpowered USB hub (bad setup) with no problems so I think you should be fine.
  3. SXR macrumors 6502a


    Nov 20, 2007
    I have never experienced my MacBook going into battery power when plugged in.I dont think that this is supposed to happen either.
  4. grahamnp macrumors 6502a

    Jun 4, 2008
    It really shouldn't be happening but many users of the higher end 15" and 17" 2011 MBP are having their batteries depleted under heavy load because the magsafe doesn't supply enough power.
  5. Tomb01 macrumors 6502

    Jan 6, 2009
    Colleyville, TX
    But it does

    Unfortunately, the new quad core processor combined with the new GPU often draws more power than 85W. It is 'functioning as designed' for the system to shift to battery power if that occurs...
  6. Primetime89 macrumors member

    Feb 16, 2011
    Yes I have this problem with SC2. Also read it's functioning as designed which is kind of hard to believe.
  7. GGJstudios macrumors Westmere


    May 16, 2008
    Yes, Apple notebooks can draw on both AC power and the battery during periods of peak power demands. They are designed to do so. For details, read the "AC Power" section in the link below. No, an external drive that is AC powered will not also draw on bus power.

    This should answer most, if not all, of your battery questions:
  8. Sossity thread starter macrumors 65816

    May 12, 2010
    I have read about the notebook batteries, & I am using the 2010 i7 unibody macbook pro with built in non removable battery.

    what happens when it's battery can no longer hold a charge? or is essentially dead & can not be recharged any more? can I continue to use my laptop plugged into the AC power strip with the 85watt power cord? if I am using just the power cord with a battery that no longer works, what will happen when I am using the computer under heavy load, & the power cord does not supply enough power, & has no live battery to dip into? what would happen then?

    at this point when this happens is my laptop then essentially no good? I think apple needs to redesign the power supply, as the power demands & capacities of the laptops increase. I bought this laptop hoping it would last me at least 2 years but ideally 3 or more years, it was quite expensive.
  9. GGJstudios macrumors Westmere


    May 16, 2008
    Then you should have it replaced.
  10. iMacDragon macrumors 68000


    Oct 18, 2008
    Hmm, seem sto be hit and miss actually, just tested mine curiously, running portal + a handbrake encode, which should be pretty much maxing out system, also put screen brightness on max and mine is still only drawing from AC. Perhaps it depends on luck of draw on how energy hungry your CPU is, as there is variance on this ( intel set the exact voltage requirements of each cpu at the factory, some are lower than others. )
  11. JTToft macrumors 68040

    Apr 27, 2010
    Aarhus, Denmark
    I realize that this is an old thread, but I thought I would add some info.

    Regarding power drainage when using external hard drives: I am experiencing a huge dip in battery life when using an external hard drive with my MacBook Pro (15" early 2011). My computer is currently running on battery power (no MagSafe connected), and it reads 4:46 at a 63 % charge. Now, this is perfectly fine. But when I plug my LaCie d2 Quadra hard drive into the FireWire 800 port on my MacBook Pro, the estimated time remaining drops to 2:34.

    This is definitely because of the LaCie drive. Pretty much the moment I unplug the FireWire cable, it goes back up to around 5 hours.

Share This Page