Having 22 hard drives on a 750W PSU

Hi everyone,
I am planning to add more drives to my build since I figured out a way to cram in more hard drive. I am currently at 16 and plan to add 6 more. I know that spin up can consume up to 25W and that my gold rated PSU is 87% efficient, which leaves me with 650W effective power. If all drives spin up at the same time at boot time, that would be a load of 550W. So I have basically 100W to spare for the CPU, motherboard and the 9 fans I have in the case for the boot time only. Once spun up, the drives would consume only 110W so not a big deal and I could then start plotting with the 3900x that consumes up to 145W.

Do you think this could work?
And is anyone else here running a similar setup?

I have 32 drives per 850W PSU - these are dedicated to disks though, so 22 on a 750W doesn’t sound too worrying.

I base this not only on the W rating, but how many connectors you could put onto the PSU without using multiple splitters, for e.g. I use NZXT C range modular PSUs for everything (so I can safely swap modular cables around), on one PSU I can have 4x3 (12) molex connectors using the provided modular cables, these plug into backplanes that have 3 disks per molex connector (4 disks on some actually), so that’s at least 36 disks (32 chosen for convenience though, since everything else is in multiples of 8), so practically leaves a few connectors free for fans.

I have a Corsair RM750x. And I do indeed use Y splitters Molex to Sata. I plan to mount up to 6 drives on one single peripheral output from the PSU. I have 5 outputs, so I’d be mounting 3, 3, 3, 6, 7. Let’s hope nothing blows up. I also have Y splitters Sata to Sata so I might be better off doing 4, 4, 4, 5, 5.
My PSU came with three 3x sata connector cables and two 4x molex connector cables

There’s a lot of online scare about molex to sata adapters, but as long as you’re buying high quality ones, and as long as you’re not connecting splitters into splitters I wouldn’t be too worried myself - the power side of a SAS backplane is pretty much a molex to sata splitter with extra steps

Well, I have been buying the cheapest ones I could find on eBay. I think such a splitter with 40W peak power and 10W constant power does not represent a big danger. And yes, I do not plan to plug splitters into splitters.

Eh, that and power supplies are the 2 things I wouldn’t go too cheap on - the molex side is almost certainly going to be fine, they are overkill for multiple reasons (big well spaced connectors, thick wires), the risk with cheaper molex to SATA is (apparently) that the ones with moulded plugs can have shorts on the SATA side (tiny pins moulded could easily end up too close), still, I’ve used them in the past and never even heard about this until recently.

Here’s what to look out for:

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Okay thanks I’ll consider that. Also another question: If I understand correctly the 12V rail is connected equally to all 5 peripheral connectors on the PSU. So in theory it should not matter how much power you pull from each connector as long as the total is not higher than the max power?

The only thing that matters then is the rating of the wires and the connectors - you shouldn’t be able to pull too much over the molex connectors, it’s something insane like ~10A per 12V pin, at the SATA pins you’ll only be pulling power for the disk, or at most 3 disks if you’re using 3 way SATA splitters (where the same applies about quality of the SATA connector - there’s nothing intrinsically bad about molex to SATA, just that apparently there are a lot of low quality SATA connectors on those products).

PSU’s also have a separate rating for 5V and 12V, hard disks use both. Mostly specs or label will tell you max Amps for 12V and 5V
A 550W PSU might very well have the same 5V rating as a 850W PSU, the high ratings are mostly designed towards the 12V pcie graphics cards

Check the capacity peek your PSU can manage. That is relevant for the spin up. Also what other hardware do you have in the system and how busy it is? 750W is not much. Better get a bequiet dark power pro 1500W or similar

I have been running into trouble with running too many HDDs with a single PSU, where some HDDs would disconnect every so often. I have dug out an old PSU to run in parallel with the existing device PSU using this connector, works a treat. Just to be clear, my pc is currently running 2 PSUs.

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Can also use something like this if you don’t want to lose a molex connector:

Slightly more high-tech version of sticking a paperclip across the right pins :sweat_smile:

https://www.amazon.co.uk/MagiDeal-Supply-Splitter-Adapter-Computer-Black/dp/B0795NZW7R

I have a setup for 24 disk with 750W Gold as well, as I use HBA card to link the HDD,
as I heard that the HBA card will control to boot the disk sequentially when reboot ,not at spin
all disk at once, so ,should be fine.

I think you need a little more overhead. but it could work.

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I use a HBA card (Dell H310) flashed into IT mode. But no idea if this does stagger the spin up.