Required PSU Power for 12 HDD SATA 7200RPM (i have 20 A on my PSU peripheral channel)

I have a Tower server with today many hard drives and i would like to add hard drives for securing a raid group and also to extend storage capacity.

Hardware spec before adding everything else :

• PSU : ENERMAX REVOLUTION D.F. 850W 80+ gold (20Amp for +12 peripheral like SATA and Molex 4P)
• Motherboard : SUPERMICRO X8DTL-3F CPU : 1
• XEON X5687 @ 3.60GHz RAM : 8GB RAM DDR3 1333Mhz (NO-ECC MEMORY /
• STANDARD DDR3)
• HDD : 9 SATA HDD 7200RPM + 1 SSD 256GB
• PCI : LSI SAS9211-8i 8-port 6Gb/s PCI-E
• 5 fans including CPU FAN (2 or 3 of 5 powered by motherboard)

I would like to add 3 more HDD SATA 7200RPM, it is possible with my 20A +12vdc 850W PSU ?

I have calculated 1.5A on 12vdc for 2 HDD so 750mA per 7200 3.5" SATA HDD, so it would consume for 12HDD arround 9A or ~10A. Thanks

A 7200K RPM drive requires about 15-20W during spinup, so 12X such drives would command a peak of about 200W from the combined 3.3V / 5V rails.

I see no problem for your 850W PSU, especially considering it is an high quality Enermax 80+ gold unit. At worst, you can split your drives between the different PSU rails to avoid overloading a single one.