front panel USB3.0 port question

[khonghinglee]

I have a question regarding the power output of the front panel USB 3.0 ports powered by a mini-pcie 2-port USB 3.0 card. The card has an additional power cable connected to one of the molex power connector from the power supply. I have no issues when I connected the following device combinations to the 2-port front USB 3.0:
- 2 thumbdrives (1 on each port)
- 1 thumbdrive and 1 external 2.5" HDD
However, when I connect 2 external 2.5" HDDs (one on each port), then the problem of the HDDs spin-up retries happens. I suspect the problem is due to insufficient power to power 2 HDDs at a same time.

I understand the USB is powered by the 5V rail, and each USB 3.0 port can output 900mA. My power supply is the Silverstone ST45SF-G 450W. The specs of the power supply can be found here. As the 5V rail is 14A, it should be more than enough to power the external 2.5" HDDs. Why does the problem of insufficient power still occurs? Is it the limitation of the USB card or is it the power supply?

Since I am using this PC as a NAS, the specs are quite basic:
- Intel Atom D510MO itx motherboard
- 2x 750GB sata HDD
- 1x 32GB SSD
- 1x PCI sata raid card.
- 1x mini-PCIe USB3.0 card
- 2GB DDR2 ram.
- 3x case fan (2x 80mm front + 1x 140mm rear)
- Silverstone ST45SF-G power supply.
- Fractal Design node 304 case (white)

 

[royfrosty]

I may be wrong. But the wires you using, is it a long or short ones? The one that connected the HDD to the front USB3.0

 

[khonghinglee]

I may be wrong. But the wires you using, is it a long or short ones? The one that connected the HDD to the front USB3.0

The USB 3.0 cables are the ones that come with the HDD casings. Its not that long, roughly 30cm or less.

 

[FinalTidus]

My suggestion is whenever you are connecting external hard disks which require substantial power, connect behind the motherboard where the ports are directly powered and connects directly to the motherboard chipset.

These ports offer the best performance and stability in providing power.

The front ports might not be providing sufficient power to devices that need a lot of power. However they are sufficient for thumb drives and USB wifi adaptors.

I also have problems when I connect to the front ports. But no problem when connect behind the motherboard.

Of course USB wires also play a role. Avoid those very thin wires that are solely for charging of handphones as these wires are very finicky.