Hi.

I have a storage case from inter-tech, where there are 24 HDD bays. I have WD Red disks. I will power them with a Seasonic Focus GX-750W power supply. There are backplanes in the case. 1 backplane = 4 HDDs with 1 molex for power. A total of 6 backplanes and 6 molex connectors. Since I didn't have enough molex cables, I ordered cables from cablemod. 1 cable with 3 molexes. I have 3 of these cables. Can I power 8 HDDs with one cable with 2 molexes?

Can I power all 24 disks with 3 cables? Each cable will use 2 molex connectors.

The disks consume 2A (24*2=48A) when spinning. The Seasonic Focus GX-750 has 62A for 12V. So will the power supply handle it?

10 hours ago, Arnavisca said:

1 cable with 3 molexes. I have 3 of these cables. Can I power 8 HDDs with one cable with 2 molexes?

Can I power all 24 disks with 3 cables? Each cable will use 2 molex connectors.

Not an ideal topology.

But with Seasonic Focus GX-750W power supply, you basically haven't any choice, it have 3 SATA power socket only.

4 IDE/SATA/MOLEX socket

5 hours ago, Arnavisca said:

4 IDE/SATA/MOLEX socket

Yes

The "correct" way was joint the 4 wire and then split to 6 molex plug. Molex use 4 wire, so you will have 4 joint and each joint have 10 wire ( 4 in and 6 out ).

This will equally share the loading to 4 wire, as result minmize the voltage drop.

Edited October 15, 2025Oct 15 by Vr2Io

I don't know if I understand. Can I just connect it like this?

As reply, this not an ideal topology, if you can't DIY then not much you can do.

Molex plug / socket not design to handle too much loading.

Edited October 15, 2025Oct 15 by Vr2Io

13 minutes ago, Vr2Io said:

As reply, this not an ideal topology, if you can't DIY then not much you can do.

Molex plug / socket not design to handle too much loading.

OK, I understand. One more question. If I only have 16 drives and I'm going to power them 4x (1 cable with 3 molexes - only one will be connected). So 4 cables in total. Is this combination okay?

2 minutes ago, Arnavisca said:

OK, I understand. One more question. If I only have 16 drives and I'm going to power them 4x (1 cable with 3 molexes - only one will be connected). So 4 cables in total. Is this combination okay?

Yes, this should be most accepted case, one molex for 4 device

1 minute ago, Vr2Io said:

Yes, this should be most accepted case, one molex for 4 device

7 minutes ago, Vr2Io said:

Yes, this should be most accepted case, one molex for 4 device

If I want to power 20 disks, I need 5 SATA/MOLEX slots and for 24 disks, 6 SATA/MOLEX slots. And will everything be ok? Just 4 HDDs - max 1 cable with 1 molex.

So for 20/24 disks, I need a 850/1000W power supply.

19 minutes ago, Arnavisca said:

f I want to power 20 disks, I need 5 SATA/MOLEX slots and for 24 disks, 6 SATA/MOLEX slots. And will everything be ok? Just 4 HDDs - max 1 cable with 1 molex.

So for 20/24 disks, I need

Yes, this usually fine. The main problem are Molex not suitable for handle too much power, the metal are thin and connection also not strong, that's same reason as we found heavy house appliances always not recommend use plug and socket.

24 minutes ago, Arnavisca said:

So for 20/24 disks, I need a 850/1000W power supply.

This not true, for 24 disks, this need ~280w. Higher rating power supply wont help. The key point are how we properly and safe enough delivery the power to device.

18 minutes ago, Vr2Io said:

Ano, to obvykle funguje. Hlavní problém je, že Molex není vhodný pro zvládání příliš velkého výkonu, kov je tenký a spojení také není pevné, ze stejného důvodu, proč jsme zjistili, že u těžkých domácích spotřebičů se vždy nedoporučuje používat zástrčku a zásuvku.

To není pravda, pro 24 disků je potřeba ~280 W. Vyšší jmenovitý zdroj nepomůže. Klíčovým bodem je, jak správně a dostatečně bezpečně dodat napájení do zařízení.

I thought these power supplies had a lot of SATA/MOLEX slots - 5/6.

Just now, Arnavisca said:

I thought these power supplies had a lot of SATA/MOLEX slots - 5/6.

Yes, this could avoid DIY. But they usually not provide all wire set. You need purchase yourself.

8 minutes ago, Vr2Io said:

Yes, this could avoid DIY. But they usually not provide all wire set. You need purchase yourself.

One more thing. Will it be a problem if an 850/1000W power supply only draws 100-250W?

1 hour ago, Arnavisca said:

One more thing. Will it be a problem if an 850/1000W power supply only draws 100-250W?

There are no problem.

1 minute ago, Vr2Io said:

Nejsou žádné problémy.

Thanks a lot for the answers.

Just to comment, as I'm was a similar situation.

1. It's not ideal, by any means, and you run the risk of shorting the drives. (I've personally had this happen)

2. Option: Get a power supply with 6 SATA connectors. I have a Corsair HX1200 v2 and I have 7 drives per SATA connector.

3. Option: Seing how HakoForge and 45drives do their power spliiting from PCIe GPU power connectors, I found this on a certain Chinese online site my friend Ali recommended under the name "ATX 6/8Pin 12V to 5/12V 4x 4PIN + 4x 5PIN Power Supply Breakout Board Module Adapter Connector for ATX PSU 2.5/3.5" SATA HDD". One PCIe GPU split it into 4 connectors which provide stable 12v and 5v. I have between 4 and 5 drives attached per molex connector. Each power connector can handle max 3A. (FYI: this is work still in progress, so the build is FAR from done).
   

Edited November 14, 2025Nov 14 by PeterDB

I was just researching this, the molex spec says 11A per pin, a single Exos X20 requires 9.8W let's assume it draws everything from the 12V that's 0.833 A. Meaning one molex connector could theoretically drive 13 drives at once, I would not drive more than 10 or 11 at once, to keep a margin of error.

9 hours ago, silajim said:

I was just researching this, the molex spec says 11A per pin, a single Exos X20 requires 9.8W let's assume it draws everything from the 12V that's 0.833 A. Meaning one molex connector could theoretically drive 13 drives at once, I would not drive more than 10 or 11 at once, to keep a margin of error.

Problem is that this spec on the drive lists the running power draw. It does not specify what the startup (inrush) current draw is when the platters are being spun up. This can range as high as 3 amperes— very old number from many years ago. (I don't know what modern drives' startup current but a rule of thumb is to figure 2 amperes and you will never be wrong. You also have to use this number when sizing the power supply because Unraid spins up all of its drives simultaneous during is normal operation– one reason why PS with a single +12V rail are recommended. One must realize that modern PS will shutdown if the max current rating is exceeded after a few milliseconds.)

10 minutes ago, Frank1940 said:

Problem is that this spec on the drive lists the running power draw. It does not specify what the startup (inrush) current draw is when the platters are being spun up. This can range as high as 3 amperes— very old number from many years ago. (I don't know what modern drives' startup current

Full datasheet has it.

https://www.mouser.com/datasheet/3/47/1/96HD20T-ST-SG7KE_datasheet20230308183452.pdf?srsltid=AfmBOoqGB8-fDhFlNpufHzNxngKCPyYokATutRDfNKTAoscWDC0wOanv

The biggest worry with the MOLEX connector is the IR drop during startup. This can be compounded if they are in series. Probably a good rule would be two MOLEX/SATA connectors in series.

And don't even talk about SATA power connectors. That design is the poster child for how not to design a connector! I don't even think using a SATA-to-SATA splitter is a good idea in a server environment.

This is the ideal design for a MOLEX-to-SATA power splitter:

Notice that there is a max of 4 SATA connectors. Also observe that the wire is continuous and the connection is made by displacing the insulation with a blade on the terminal in each connector. (Avoid molded in wires as defective manufacture of the cable can result in a known fire hazard!) This should be plugged directly into a MOLEX connector on the +12V cable from the PS.

Edited February 27Feb 27 by Frank1940

1 hour ago, Frank1940 said:

The biggest worry with the MOLEX connector is the IR drop during startup. This can be compounded if they are in series. Probably a good rule would be two MOLEX/SATA connectors in series.

And don't even talk about SATA power connectors. That design is the poster child for how not to design a connector! I don't even think using a SATA-to-SATA splitter is a good idea in a server environment.

This is the ideal design for a MOLEX-to-SATA power splitter:

Notice that there is a max of 4 SATA connectors. Also observe that the wire is continuous and the connection is made by displacing the insulation with a blade on the terminal in each connector. (Avoid molded in wires as defective manufacture of the cable can result in a known fire hazard!) This should be plugged directly into a MOLEX connector on the +12V cable from the PS.

There is a reason for 4, which is the old rating for 3A per disk during inrush/power on, and that most older PSUs only delivered 12A per molex connected (4 connectors X 3A = 12A).

However, a good high voltage platinum or titanium single rail PSU can easily handle 50A. My Corsair HX1200v2 can handle 100A on the +12V rail, and 30A on the 5V.

Only considering the 12V rail that would be 33 disks. Now if you do that all on one single string the cable would be the limiting factor. If the PSU can handle it then really it becomes the cables AWG rating that needs to be looked on. On a 17 AWG cable, which is the max you can fit in a molex connector using a punch (higher if you solder) then it's 14A, and then we are back at 4 disks if considering 3A inrush.

But!

Disks don't use 3A inrush on the 12V rail, it's split usually 2-2.4A on 12V and 0.2-0.8A on 5V. Added to this, if you have a decent native HBA controller like a higher end LSI, HPE or better yet Adaptec, then staggered spin up is part of the basic firmware. Even Unraid itself will stagger spin up on shutdown or all disks active.

What does this mean? Make your own cables and max 7-8 per cable!

8 minutes ago, PeterDB said:

Even Unraid itself will stagger spin up on shutdown or all disks active

I am not so sure about that..

I just spun up the disks on my array and it appeared to happen is less then three to four seconds. (I was hitting the refresh on the browser.) Here is the log:

I don't see any indication of any delay...

I do know that there is a straggled delay if you are doing a directory scan/search on a User Share that covers multiple disks but there seems to be times when all disk are spun up simultaneous (or close to it.)

3 minutes ago, Frank1940 said:

I am not so sure about that..

I just spun up the disks on my array and it appeared to happen is less then three to four seconds. (I was hitting the refresh on the browser.) Here is the log:

I don't see any indication of any delay...

I do know that there is a straggled delay if you are doing a directory scan/search on a User Share that covers multiple disks but there seems to be times when all disk are spun up simultaneous (or close to it.)

Valid point, I just checked myself and you are right (don't hear that a lot online :) )...

Command is issued but the Adaptec 71605 HBA I'm using is causing the staggering, not Unraid.

2 hours ago, Frank1940 said:

a max of 4 SATA connectors

I will stick to this advice instead of confusing users with designing their own cables 😉

4 minutes ago, trurl said:

I will stick to this advice instead of confusing users with designing their own cables 😉

While I agree that regular users shouldn't attempt this, but I consider Unraid users and users who reach this thread ones who do need more help and often do need to look into making their own cables. I'm personally already at 27 disks, and building an enclosure to fit 40+