Hi guys,

I have a DIY file server with 40 HDDs. Only issue is power supply because moder ATX PSUs usually have max. 20-25A on 5V rail, while 12V rail is overdesigned for hungry GPUs.

I have place for another 80HDDs, but I do not like power efficiency and hooking up 6x PSU, each barely 20% load and poor efficiency.

I use Seasonic Prime-TX PSUs with up to 97% efficiency at 50% load. Problem.is 20-25HDDs overload PSU durimg the cold start/spin-up stage.

Modern HDDs have usually 0.5-1A@5V rail. Seasonic handles +30% overload before protection kicks in.

Idling HDDs are not problem. Manufacturers do not share much info about power use...they state 6-8W idle/light use but what rail 5 or 12V...nobody knows but it is possible to measure it of course.

I have seen an adapter for Corsair PSUs that uses PCIe 12V rails and convert it to 5V for PC tuners.

I recall various breakout boards fir server PSUs so I am betting it is possible.

Can someone provide more info or even design PCB/IC (no issues to sponsor greatest minds on Earth)

I am not electronics guy, I know only fundamentals.

Is it possible to design an IC/PCB that takes standard industry PCIe connector with 3x12V wires (PCIe cable limit is 150W ~ 3x 12V@4A) and converts it to standard Molex connector, please?

Molex has got 1x12V and 1x5V wire, which can be easily hooked up to Molex/SATA adapter for powering HDDs.

I have no idea how voltage/current is regulated in PSU and HDD. SATA connector can handle 1.5A on each 12V and 5V pin.

Common connection of HDDs is single SATA cable with four connectors. 1st drive may have up to 4A flowing via connector.

Psu 5/12V pushing 1A for each drive > 1st hdd connector 4A > 2nd 3A > 2A > 1A. I have no idea how exactly it works but I have successfully used 5x SATA (4+1SATA adapters via Molex that can handle 10A).

BackBlaze storage provider runs successfully 5xSATA on one cable for years without any HDD failure...I bet it works

My objective is to fully utilize one PSU in order to run it at 50% load and max efficiency.

Right now I have 1kW/25A PSU powering server + 20 HDDs and second 750 W/20A powering 20 HDD

Average power consumption 290W with 2x PSU, which is poor efficiency about 90%.

It would be great to use only one PSU. 290W on 750W is about 95% efficiency. It is 5% energy saved. Server runs 24/7 and it saves about 100€/year.

During cold start about 500W spike for less than 10seconds

Any suggestions, please?

 

Perfectly possible. You might get around 95% efficiency with careful design...

Have you considered not using ATX supplies but using off-the-shelf standard 5v and 12v switched-mode supplies? Obviously will need a custom cable harness and maybe a custom interface board to handle switch-on/off sequencing and fault management. Also the interface board could sequence the start-up to avoid the power-on surge. Actually you could do that for your current set-up.

How much current on 12v and 5v does each HDD actually require?

 

Thanks for reply.

I want simplicity. Best solution would be using cables I already have. In attachement is current standard setup.

Power-up sequence is not much problem. It can be always on, problem is recovery after power failure. I can switch on/off server remotely.

I have never seen HDD which uses more than 1A on 12/5V - I am not sure but SATA standard is max 1.5A.

I will check out.

I have found yesterday "switch step-down regulator". 12V input 5V/1.5A output.

No idea about efficiency. It makes me wonder if simple soldering on official cable can do the trick.

 

According to Molex SATA spec attached in PDF, there is at least 1.5A per pin.

SATA power connector has got 3x12V + 3x5V pins. Each group of three pins is hooked up to single wire coming from PSU.

It may explain max 4 HDDs per cable (4A max current 4x 1A max forveach drive)

Standard Molex 4pin connector handles up to 11A per pin. Every PSU provides cable with 2-4x Molex 4pin connectors.

Peripherial rail of PSU, aka PCIe 6pin, handles max 75W officially. I have asked PSU manufacturer and nobody was able to tell what exactly means 75W.

Is it 75W per wire or for whole cable? They use 18AWG cables so limit is usually in connectors.

12V wire @ max 4.5A = 54W + 5V@4.5A = 22.5W or 76.5W but Molex 4-pin connectors can draw more current. No idea whether officially but 12V @ 8.5A = 105W

 

Final limit of PSU side connector is 7A per wire according to Seasonic tech support...if overloaded, PSU switches-off rail in order to stop fire, explosion.

Theoretically 7x HDD per cable

8pin PCIe has got 3x12V wires in standard spec. PSU has got up to 6x PCIe 8pin connectors/cables...theoretically another 30-40HDDs may be hooked with 12>5V regulator connected