Issues with HD's external power supply

Hi to everyone,

I'm in a little trouble with the 3,5" hd connected to my rpi.
I use an external box adapter with the 5V power plug. The external power supply gives 1.5 A, the HD requires 700 mA to works.
There's no way to view the hd, I tried a lot of 5V power supply, even when powered stand-alone without a power-strip.
I've also tried a power bank.
That box connected to my pc (so, without the 5V power), works great.

3 questions:

• any suggestions for my problem ?
• Is there some option to manage the power supply via software ?
• may I use an usb key as external drive ? (I do not need so much space, although it is a pity). If so, any key to suggest ?

Thank you !
Luca

Filesystem EXT4.
It seems to be a rough electric issue.
I tried 4 power supply, the same used for cellphones, all of them 5V and 1.5 A. It not seems to be differences between them.
1 on 4 works fine, the hd is working, but i didn't understood why.

However, i think i've asked something out of the scope of this forum...
I was curious about other member's experience about external hd's power supply.

Thanks a lot !
Luke