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My question here is about electrical safety of a proposed PSU cable hack.

The situation is a single rail 1600W PSU (to avoid partitioning of the current) that has to power some 20-24 HDDs.

I've asked about PSU size elsewhere and I don't need product help - this question is purely about whether it's electrically safe to use an apparently-simple PCI-to-MOLEX/SATA cable hack, to power some HDDs.

HDDs are powered by chained cables, but splitters and chains have a current limit. If they all max out at 3A current, which these do, then potentially 8 HDDs on a 4-ways chain with splitters, would mean 24A on a single MOLEX/SATA cable of at most 16 gauge, and perhaps only 18 gauge. Far above MOLEX/SATA cable spec, and fairly soon it would mean meltdown time for the cable, with 100A+ just waiting to short out.

Ideally I'd like to limit the drives to 3-4 per cable, which means (say) 8 PSU connectors x 3 drives per connector, or 6 PSU connectors x 4 drives per connector. But most PSUs that are electrically, financially and acoustically sensible, have up to 5 HDD connectors, and I'd like to spread the load across more than that number of connectors/cables.

At the same time, all of the PSUs have 3 - 6 PCI power connectors connected to the identical rails, providing identical voltages, that are completely unused, because high quality high power PSU are mostly used for multiple PCI/VGA (which I don't need), not dozens of HDDs.

My understanding is that the PSU PCI connectors are basically identical electrically to the HDD connectors. They provide the same voltages from the same rails (on a single rail supply anyhow). The only real difference is that their pins assignments may be different at the PSU end (that is, for some specific PSU, the HDD connector may be assigned pin1/3=12V, pin2/4=GND, etc, while the PCI connector may be assigned pin1/2=12V, pin3/4=GND etc)

I have spare compatible plugs for the PSU end, and spare compatible chain cables for an HDD end. I can't see a reason why it wouldn't be completely electrically safe to hack a PCI "PSU end" to an HDD "chain end", if I'm careful about checking which wires carry which voltages, and basically treat the 4-6 PCI power sockets exactly like extra HDD power sockets.

Assuming I'm competent to check voltages and solder/insulate the cables appropriately, and I don't power more than about 3 - 5 HDDs off a hacked cable (to not overheat the joint), is there any reason this wouldn't be an electrically safe and sane way to spread the load across more HDD cables?

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    \$\begingroup\$ Hard drives also need 5V, you should find a way to get that as well. \$\endgroup\$ – Pentium100 Dec 11 '17 at 20:40
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If you look at the sata power connector you will see +3 +5 and +12V:
sata power pinout

Now compared to the PCI Express power connector:
pci express power peg pinout

You will see that you are missing +3 and +5 Volt. It will depend on the exact type of hard drive used if that can function with only the +12V rail supplied.

Maybe some drives will. WD Red for example does not specify a load on the 5V rail.
So that might work, since the old ATX 4-pin to Sata do work, and those do not even contain 3.3V.

This might be different for 2.5 inch drives.

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  • \$\begingroup\$ Bugger. (I mean, thank you but grumble. HDD does indeed draw 5v) \$\endgroup\$ – Stilez Dec 11 '17 at 20:56
  • \$\begingroup\$ @Stilez It appears that some do not. \$\endgroup\$ – Jeroen3 Dec 11 '17 at 20:57
  • \$\begingroup\$ Unfortunately the enterprise drives I've got, do... \$\endgroup\$ – Stilez Dec 11 '17 at 20:58
  • \$\begingroup\$ @Stilez Then just get a storinator or something. \$\endgroup\$ – Jeroen3 Dec 11 '17 at 20:58
  • \$\begingroup\$ 3.3 volts is optional for all SATA drives, this the 4-pin Molex-to-SATA power adapters. \$\endgroup\$ – DoxyLover Dec 11 '17 at 23:56

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