Is an external hard drive supposed to cut my battery life in half?

Discussion in 'MacBook Pro' started by JTToft, Apr 18, 2011.

  1. JTToft macrumors 68040

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    #1
    Hello all.

    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.

    I am seeing roughly the same numbers (4:42 to 3:10) on my Western Digital MyBook Studio Edition with FireWire 800. However, when using USB 2.0 with either drive I see no drop at all.

    Does FireWire really consume this much power?

    (Both drives are powered by their own AC adapter)
     
  2. Hellhammer Moderator

    Hellhammer

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    #2
    Have you checked your CPU usage in Activity Monitor? Maybe the LaCie is launching some process that uses a lot CPU
     
  3. -aggie- macrumors P6

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    #3
    It's probably Spotlight indexing the drive. Check you Activity Monitor. Turn off indexing for the external drive.
     
  4. JTToft, Apr 18, 2011
    Last edited: Apr 18, 2011

    JTToft thread starter macrumors 68040

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    #4
    - I have now. There is nothing of the sort. Even if there were, it wouldn't explain the drainage when using the Western Digital drive on FireWire 800.

    But thanks for your contribution! What kind of process did you have in mind?

    - It is not. If it were Spolight causing this, the battery life should also drop when connecting with USB.
    Furthermore, it drops permanently. It is not like it drops for a couple of minutes and then goes back up (which should be expected were it caused by Spotlight indexing). It stays down there.
     
  5. VTMac, Apr 18, 2011
    Last edited: Apr 18, 2011

    VTMac macrumors 6502

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    #5
    That LaCie drive can draws up to 8 watts from the firewire port. Your MBP battery is 77.5 Watt-hours. That basically means that extrenal will use 1/10 of your battery capacity per hour. So if you start with approx 7 hours until light load, that means the rest of your MBP is drawing about 1/10 of your capacity per hour.

    So the answer to you question is clearly yes. That drive should in general cut your battery life exactly in half, as it's like having another computer pulling on the battery at the same time.
     
  6. -aggie- macrumors P6

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    #6
    Sorry, missed the part about checking on a USB
     
  7. Hellhammer Moderator

    Hellhammer

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    #7
    Makes no sense since the ext HD has its own power supply, thus it should not draw any power from the FW800.
     
  8. VTMac macrumors 6502

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    #8
    That would have been good info to have in your original post.

    Then I would suggest that perhaps your LaCie has a bad power supply and it is drawing current from the FW port. I've never owned a LaCie, but I've seen literally thousands of reports of bad power supplies on these drives. As best I can tell they are notorious for this. If you have another, try a different power supply on the LaCie.

    There is no magic here. If the battery life goes down, it's because current is being drawn by the connected device. And IMO, it's a bit too coincidental that the exact power draw the LaCie drive just so happens to correspond to the exact battery life reduction you are seeing.
     
  9. JTToft, Apr 18, 2011
    Last edited: Apr 18, 2011

    JTToft thread starter macrumors 68040

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    #9
    - Interesting! Thank you.
    But should it draw this much power even when it has its own power supply?Do you have some documentation on this? And what about the Western Digital drive?

    - That is quite alright. Just to check, I did as you suggested and turned of indexing of this drive in Spotlight's preferences. No change.
    But actually, you just reminded me that there is no reason for spotlight indexing my backup drive, so thank you. :)
     
  10. borisiii macrumors 6502

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    #10
    It's strange that it's happening with those two drives since they are 3.5" and therefore should have their own power supply.

    FireWire is a high-power interface meaning that, if required, it can deliver a high current to an external device. If your drives were 2.5" the drop in battery life would make sense given that your battery would be having to supply power to the hard drive as well as your MacBook however, since they should be self-powered, it is strange you are seeing this.

    It could be that, for some reason, your particular drives draw maximum power over FireWire all the time, which is something I have seen in the past with some devices (like an old four-way FireWire hub which drew power even when no devices were attached) but not with hard drives.

    My only advice would be to try an SMC reset, and if that makes no difference, consider whether you need the speed boost of FireWire over USB.
     
  11. JTToft thread starter macrumors 68040

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    #11
    - That info was in my original post.

    And if it is caused by a bad power supply, then why does the drive work fine with a USB connection without drawing any power?
    And what about the Western Digital drive?
     
  12. JTToft thread starter macrumors 68040

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    #12
    New info:
    I just tried connecting the LaCie drive with a FireWire 800 to FireWire 400 cable. I am seeing the same 2 hour decrease in battery life.
    It is also worth noting that it is necessary to unplug the FireWire cable to get the estimated time remaining back up - merely ejecting the drive in Mac OS X makes no difference.

    It would be interesting to see if others are experiencing the same. Could someone check this behaviour on their MacBook Pro? That would be great!
     
  13. blevins321 macrumors 68030

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    #13
    That is very odd. Does the drive spin down and/or power off when you eject it?
     
  14. blueroom macrumors 603

    blueroom

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    #14
    Since the LaCIE has external AC power why are you running the MacBook on battery?
     
  15. JTToft thread starter macrumors 68040

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    #15
    - It spins down. It does not power off.

    This goes for both the LaCie and the WD. Ejecting the drives does nothing. I have to disconnect the FW cable in order for the batttery life to go up again. It is also interesting that with the WD drive turning it off has no effect - I have to disconnect the FireWire cable. With the LaCie, however, turning it off does cause the battery life to go back up.

    If I connect the WD to my computer with FireWire only (meaning no AC adapter on drive nor computer), the battery life decreases! With the LaCie, it does not.

    - To test this power consumption issue.
     
  16. Blipp, Apr 18, 2011
    Last edited: Apr 18, 2011

    Blipp macrumors 6502

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    #16
    Isn't that kind of pointless? If your external REQUIRES you to be near an outlet to use it then who cares how it behaves when your MacBook Pro is running on battery power? What scenario do you see yourself being in where you have only a single socket available and you absolutely must use your rather large external HDD for more than the 2.5 hours your MBP battery is estimating?

    Further more that time estimate is based on current activity, have you tried actually allowing your MBP to die while the HDD is connected and timing it? You may actually get more real-world time out of it than the timer is predicting. Your computer may be factoring in the drive drawing power from the battery when it in fact is not or the drive could draw power regardless of its own power supply. Check the user manual and see if says anything about recommending using a power supply when connected to a laptop.
     
  17. JTToft thread starter macrumors 68040

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    #17
    - I see your point. And I only noticed the high power consumption of my external FireWire 800 drives because I forgot to plug my MagSafe cord into my MacBook Pro when I turned it on earlier today. I have been using the drives with FireWire 800 for weeks without noticing the power consumption (because, as you say, normally one has one's computer plugged in when using a large external hard drive). But when I noticed the rather poor battery life when I turned the computer on earlier today, I began investigating what was causing it and found that it was the FireWire 800 connection.

    - No, I have not tried that. I have, however, been using the computer on battery with the hard drive connected for some time, and I definitely see a rather rapid decrease in battery charge (in percentage, not remaining time), so I don't think it's merely an error in the computer's calculation of remaining time.

    - I don't see why that would be the case.

    - Yes, and it appears that it does. But why?

    - Done. It does not say anything about that.

    Thank you for your thoughts.
     
  18. Blipp macrumors 6502

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    #18
    Could be as simple as sloppy design really. The drive could be functioning as intended even though it's resulting in a less then desirable experience. My guess would be that everything is perfectly fine just maybe a little annoying.
     

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