I have read that one needs to be careful adding many SSD drives to a system because they use the 5v rail. my PSU 5v rail if 20A. How many SSD’s can I safely install? I have 5 at the moment, but want to add 4-6 more… how can I safely do this?
Are there converter boards for using more of the 12v rail on a PSU to convert more 5v power?
Or general purpose backplanes that might do this that I can jerry rig 
?
Thank you!
Either the datasheet or the label should have information regarding power draw:
Both possible, it may not even be required, see above.
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That entirely depends on the power requirements of the drives you chose.
When I did that I looked at the spec sheet and red some reviews that included power measurements during different workloads. I did this further step because I know manufacturer exceed power requirements most of the time and was the case for the drives I bought.
You could use a step down circuit to use the 12V rail instead of the 5V. They’re usually pretty cheap and available. Though I don’t know which one to recommend that’s well made and reliable since I’ve never used one.
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Normally I don’t shill for new power supplies, but with the amount of time, effort, custom wiring, and unknown quality of random converters (or expense of good converters), I would just buy a power supply with sufficient amperage for the 5V rail if the existing PSU doesn’t supply enough current. Cheap switch mode power supplies can introduce a lot of noise which could potentially cause data corruption issues, and making your own noise suppression is reinventing the wheel in a more costly manner than buying an off the shelf PSU.
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20a @ 5v is 100w. 10 SSDs drawing over 100w on the 5v rail would pretty much require enterprise hardware, such as dual link sas drives and u.2 drives.
Looking at Micron 1100 power specs, which seem to mirror crucial mx500, it’s 1.7a maximum. The max listed on the drive it’s self should be the limit of it’s internal power correction, meaning it won’t ever actually go above that, and isn’t likely even to reach that kind of power under heavy use.
Whitepaper for the 1100 backs this up, listing only about 6w as the maximum sustained power for the largest 2TB model of the drive, well below the 8.5w maximum listed on the drive it’s self.
I think you’ll be just fine without worrying about it.
Also, look at that active average. That’s normal read-intensive activity. The 3~6w maximum is large sustained sequential writes specifically and exclusively.
Even if you have enough drives to exceed the 100w as a peak value, it’s only going to happen if every drive touches that maximum peak at the exact same time, which… is very unlikely, and your power supply can probably handle 150w over 5v for that brief few microseconds if it does. But, when you have something like 17+ drives, maybe start looking into adapters or whatever, just to be on the safe side 
You can also adapt internal USB for it’s 5v power. USB2 should probably deliver enough 5v power for SATA SSDs, and USB3 is good enough for wholesale adapters if you can give up a little performance. Each internal USB header is worth 2 physical ports.
Thanks for the feedback everyone. I assume the “enterprise” setups accomplish this by having converters on the backplanes. Perhaps I’ll look into some recycled back planes and see if I can jerry rig one of those… assuming I run into issues just trying it without any
I think my 16 SAS drives pull like 150w in my JBOF (Mix of 4 and 8tb drives more 4 then 8)
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Like @alkafrazin said, until you go over 12 drives, don’t worry about it.
By then, You will want a backplane, if only for connectivity if not power…
It is interresting, seeing the possible 5v limit on a supply to perhaps approx 20% of the total, with most loads (in general, in a computer) being over the 12v rails
are SAS on the 5v power rail? doubtful. Likely 12v the controllers/backplane steps down to what they need internally.
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SuperChassis 216BE1C-R609JBOD
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I presumed this is what mine did.
Never actually checked before tho
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Seems that way as the data sheet say 4A max for 5v
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specifically for 5vsb, which is a separate 5v rail for idle power.
It looks like SAS is limited to 1.8a on 5v also. I suspect this is a limit to the SATA power adapter.
So, in other words, 20a for 5v means anything 11 drives and under won’t be physically capable of saturating the 5v rail, and you’ll likely only ever see that on mechanical harddrives spinning up during boot.
But, USB devices also pull on the 5v rail, so be mindful of that I guess. I don’t think you could actually fit enough sata SSDs to matter, unless they’re constantly being written through at their maximum data rate, in which case… you really don’t want SATA SSDs for that job anyway. Consider getting a PCIE flash accelerator for that, or optane if you’re made of money.
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