Rech. Battery powered USB hub

Discussion in 'General Electronics Chat' started by james211, Oct 3, 2013.

  1. james211

    Thread Starter Member

    May 29, 2012
    210
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    So I'm trying to figure out a solution for a product that doesn't exist, a portable, battery powered usb hub.

    So here's my thought....How hard could it possibly be to connect a rechargeable battery pack that would power a USB hub? Most seem to run on 5V's from what I've read.

    Typically I need to power portable hard drives via USB 3, which the ones I have currently draw about 225mA. But how do I figure out how many mAh it draws? I'd like to find a large enough battery to supply power for 4-6 hours.

    I know I'd need to reduce the power from a higher voltage down to 5V's, but I don't see that as being too hard.

    Think this could work?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    It could work. You'll need a DC-DC converter to take the battery voltage to a steady 5V. The battery pack will have a mAh rating.

    One problem you'll have is that some USB devices are "smart", and adjust their behavior depending on a handshake with the host. They may not charge or run properly without a successful handshake.
     
  3. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    How would the device know its not using the DC power supply (wall wort) that was intended for the hub?
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    Ah, I see your point. I thought you were making your own hub. The hub itself should handle power allocation so you can ignore the handshake issue.
     
  5. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    Any idea on how I can figure out how many mA per hour the portable hard drive draws? I know the hard drive is drawing 225mA from the computer.

    The hub I'm looking at comes with a 5V / 4-Amp power supply. So where does Amps come into play with batteries?
     
    Last edited: Oct 4, 2013
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    The drive will take 225 ma/hrs. So to run it for 6 hours you need batteries with 1350 ma/hr rating. 6 AA batteries would give you ~ 2000ma/hrs at 6volts when they were dead, so that might not be a bad choice. If you want to run several drives you can use bigger batteries. You could buy something like this to step the voltage down to 5 volts. It is pretty efficient so would only loose a little time.
    http://www.ebay.com/itm/1PCS-Lithiu...853?pt=LH_DefaultDomain_0&hash=item565bdb5b3d
     
  7. james211

    Thread Starter Member

    May 29, 2012
    210
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    Awesome, just bought two! Now, I have a fair amount of Canon BP-911 batteries available to me, but I have no clue where to find a sled that I could put a barrel plug on. Any ideas? That would be ideal since I already have batteries and charger.
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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  9. ronv

    AAC Fanatic!

    Nov 12, 2008
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  10. Jibby

    New Member

    Sep 12, 2013
    15
    1
    225mA = 0.225A
    0.225 x6 x 4 =5.4 AH Battery of 5 Volts. As such a battery is not available take a 6V battery of near that AH.
     
  11. james211

    Thread Starter Member

    May 29, 2012
    210
    2
    whats the difference between the product above and a standard dc-dc buck converter? I have LI step down above and it seems to be shorting out my batteries. I've double checked all my connection with a meter and can't find any shorts. I'm a bit confused...
     
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