# Powering 64 SATA HDD from Single ATX Power Supply

I am planning to wire a 4U DIY JBOD top loader.

Looking at the power output of several power supplies they have a a maximum rated 5v rail of 100-125w. By looking at the spec sheet of my chosen HDD I'll require more than double for all drives. There is plenty of current available on the 12v rail and I'm wondering if it's reasonable practice to use a 12v to 5v DC-DC converter?

Single drive active: 12v 0.56a = 6.72w | 5v 0.65a = 3.25w | total = 9.97w
64 drive active:     12v 35.84a = 430w | 5v 41.6a = 208w  | total = 638w


The spin-up power is well over 1600w so I'll be using staggered spin-up.

With 8 dedicated SATA power cables from the PSU I can power 8 drives on each one. The cable has 18AWG wires which should handle 8 drives over a distance of less than 300mm. There I could put an inline DC-DC converter.

Here is the proposed wiring diagram. I will not be using the 5v provided by the ATX PSU but the one from the DC-DCs. Is this a good approach, potential issues or any other thoughts?

• With something this large I wouldn't even look at a ATX PSU. I'd consider multiple PSUs at each voltage that can be slaved together. – Ignacio Vazquez-Abrams Apr 12 '18 at 17:11
• @IgnacioVazquez-Abrams, ATX12V PSUs are cheap. Anything else would cost 10X. – Ale..chenski Apr 12 '18 at 17:39
• Potential issue will be cost. You can find a server-class (blade format) PSU with 12V at 100 A (say, Murata D1U54P-W-1200-12-HA4PC) and use a bunch of 12-5V converters. And then add the cost of wiring/mounting/cooling. – Ale..chenski Apr 12 '18 at 17:43