Power boost for a 4-way USB hub

I've got a 4-way USB hub similar to this one:

https://shopping.howei.com/index.phproute=product/product&path=79&product_id=679

It works okay with pen drives, but doesn't work if I've got multiple hard drives (the small ones without external power) connected to it. Obviously because of the insufficient power supplied by a single USB port on my laptop/desktop.

However, since I2C and SPI work by keeping a floating high line powered to 5V, I began to wonder if USB works in a similar fashion. If it does, then all I need to do is plug in my phone charger which is rated as 5V and 750mA into one of the 4 USB ports and it should work. But this is just speculation and before I actually try it out, can someone please let me know if my reasoning is correct or flawed? There's a chance that I might screw up my laptop and/or hard drives if this is incorrect.

I think that you might want to disconnect +5 between the Hub and the PC (leaving the Gnd wire back to the PC alone.)

[quote author=Runaway Pancake link=topic=138638.msg1041315#msg1041315 date=1356185877] I think that you might want to disconnect +5 between the Hub and the PC (leaving the Gnd wire back to the PC alone.) [/quote]

But there's no guarantee that the PC's USB port can sink the (potential) extra current generated by the phone charger. Maybe I could disconnect the ground as well?

"If it does, then all I need to do is plug in my phone charger which is rated as 5V and 750mA into one of the 4 USB ports and it should work." "But there's no guarantee that the PC's USB port can sink the (potential) extra current generated by the phone charger. Maybe I could disconnect the ground as well?"

The PC's USB its own 5V supply and you want to run the stuff plugged into your Hub operating from a separate 5V source and have those devices available to the PC.

So, the 5V connection between the Hub and the PC should be made an open circuit. Then there won't be any conflict between those two 5V supplies. That will require modifying a cable (for between PC and Hub) or modifying one of the jacks in the hub itself (to be a dedicated connector for Hub-PC interconnect). The Gnd (Common) needs to be retained.

http://www.dlink.com.au/tech/faq/usb.htm What is the difference between self-powered and bus-powered USB hubs? A self-powered hub plugs into an electrical outlet so that it is better able to provide connected devices with power. Only low power USB devices can be connected to a bus-powered hub (like mice and keyboards). A self-powered hub will allow you to safely connect other devices that require up to the full 500mA outlined in the USB specification. D-Link offers self-powered and user-selectable self- or bus-powered hubs.

I had thought this was the big difference between a USB Switch and a USB Hub, but then I see mentions of powered and un-powered Hubs.

[quote author=Runaway Pancake link=topic=138638.msg1041631#msg1041631 date=1356205608] So, the 5V connection between the Hub and the PC should be made an open circuit. Then there won't be any conflict between those two 5V supplies. That will require modifying a cable (for between PC and Hub) or modifying one of the jacks in the hub itself (to be a dedicated connector for Hub-PC interconnect). The Gnd (Common) needs to be retained. [/quote]

Hmm, so effectively I can't really just plug in a 5V power source and expect it to work while being plugged into the PC's USB. Thanks for taking the time, but I probably won't go ahead with this since it looks a bit risky given my current knowledge levels. :~