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?

 

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.

 

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.

How would the device know its not using the DC power supply (wall wort) that was intended for the hub?

 

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.

 

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?

 

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

 

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.

 

They aren't cheap.

http://www.lowel.com/blender/blender_d.html

 

Or something like this if you have a NICD charger.

http://www.nexuscyber.com/6x-15v-aa-battery-holder?gclid=CIqR16rz_bkCFS9dQgodH3sA2g

 

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?

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.

 

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

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...