Power via USB

Discussion in 'iMac' started by digitalfailure, Dec 7, 2012.

  1. macrumors regular

    Sep 24, 2012
    Hi guys

    I've ordered a Samsung bluray drive to partner with the 27", just been reading the online specs for the drive as it hasn't arrived yet and the cable is one that uses 2 USB ports to supply enough power to the drive.

    My question is, would it still be necessary to use both on the newer iMac with its USB 3 ?
    As I understand it, USB 2 supplied 500mA but USB can supply 900mA

    Can anyone with the Samsung 506 bluray drive comment?
  2. macrumors 6502

    Nov 16, 2009
  3. macrumors 603


    I don't have the drive but I have something similar.

    I have a USB 2.5" Toshiba with a Y cable so it needs two USB slots, won't mount if on 1 port and even if I plug it into a 2 Amp USB hub it won't mount.

    Hope yours does though.
  4. thread starter macrumors regular

    Sep 24, 2012
    I hope so to :)

    My iMac isn't due to arrive until 1st week of January, so there's a while before I'll find out.
  5. macrumors 65816


    Jun 23, 2003
    Gravesend, United Kingdom

    Macs tend to be on the generous side when it comes to USB power. For a long time, iPods, iPhones and iPads have needed more than the usual amount of USB power to charge whilst being usable. My MacBook Pro has no trouble charging our iPad 2 which I believe draws 1000mA when charging – and my MBP's a 2010-vintage.

    I've used many 2.5" USB-powered external hard drives without needing USB splitters or external AC adapters. I think I've used one of those Dell DVD drives with a mini-USB connector without any problem.
  6. macrumors G5


    Jul 29, 2011
    Somewhere Back In The Long Ago
    I have a hard and fast rule when it comes to drawing power directly from my Macs. I don't. I have a powered hub that I use for the handful of devices that are not self powered...Despite what manuals etc. tell you, taking power from the USB port on any computer places an unnecessary strain on the machines PSU.

    I always purchase devices that have their own dedicated PSU, or that can be used via the powered hub. Just my 10c worth.
  7. thread starter macrumors regular

    Sep 24, 2012
    Well the drive has just been delivered days ahead of the estimated date. and the specs indicate a current draw of 1.4A so it's going to need the 2 connect plugs.

    I might invest in a powered USB hub at some point and have that in a discrete location away from the mac to cut clutter.

    What sort of current output does your hub have available at each port, would it run a cf card reader and charge an iPad 3 at the same time?
  8. macrumors 65816


    Jun 23, 2003
    Gravesend, United Kingdom
    True, you don't want to be pulling more current than the port's rated for - I've seen work PCs' USB ports fail for that very reason. But there's no harm as long as you stay within the rated maximum.

    Plus, you're at the mercy of how good the computer manufacturer's DC design is. Our el-cheapo Dells at work seem more than happy to allow you to nuke their USB circuitry. I've seen my Mac cut power to the ports if too much load is connected - I had a badly behaved optical drive cause that.

    Edit: yeah, 1.4A will need multiple connectors - but that's explicitly supported by Apple - see this tech note http://support.apple.com/kb/HT4049
  9. macrumors 603


    Powered USB with high Amp output are expensive, *you could also buy a cheap *5 Volt power brick, less expensive.

    * If your external has an extra power in plug and if it is 5 Volts, could be different.
  10. macrumors member

    Oct 12, 2012

    Very interesting, but knowing apple they probably only enable additional power for their apple devices :p
  11. thread starter macrumors regular

    Sep 24, 2012
    An interesting article for sure, I'm guessing this drive will be ok as it caries the MAC logo on the packaging. Can't see a manufacturer like Samsung adding random logos and claims unless tested and authorised. :)
  12. macrumors 6502a

    Nov 10, 2012
    I'm not entirely sure of what your question is, but this is the Blu-ray drive I'm eyeing - http://www.lacie.com/uk/products/product.htm?id=10602

    It's USB 3.0, bus powered, and while it doesn't say on that page, it should be compatible with a Mac but may have limited capabilities.

    Haven't bought it yet though.

    Also, I really recommend this for a discrete USB hub - http://www.belkin.com/IWCatProductPage.process?Product_Id=428714

    Not USB 3.0, quite expensive, but damn it's pretty neat.

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