Or even better, use separate PSU for the mobo. 
Saving some pennies could cost you much more.
I suggest you shell for a second PSU instead of trying to jury rig a possibly dangerous half solution using one inadequate power supply.
My vision of your cut rate attempt reminds me an OSHA safety video that shows the incorrect setup that caused the fireâŚ
Sure, I am pretty close to adding one more PSU, I was just considering all possible options for using the one PSU I already have. Plus discuss what is possible and what is not, having in mind that this is what should be learned in any case, either with one or with two PSU. I like to think about my self like I am going to expand my Chia farming operations.
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Im just saying again using 1 PSU for all them drives its going to melt at the main connector within 60 days.
And âthe main connectorâ isâŚ
You want a way to put all your eggs in one basket and you also want to balance 100 more eggs on the top
That would be the Gold Member wouldnât it? 
In essence this is true, most if not all PSUâs first covert AC to 12V DC and then step down to 5V and 3,3V.
Unfortunately, this does not mean you can use the full power of the PSU on the 5V connectors. This is because the hardware that creates the stepdown to 5V also has inherent power limits and fuses will have been added to ensure their safety.
So you have 25A on the 5V rail, which is just a hard limit (at least for continuous power).
If the hddâs use 0.9A 5V that means a max 27-28 hddâs. Depending on the actual power draw of the hddâs, this can vary a bit of course.
All the options I have seen are either using Jbodâs, they have their own power supplyâs that are meant for the amount of disks they fit.
Or using 12V to 5V converters and then splicing the wires to make your Molex connectors like @enderTown did in his scalable rig.
Third option is to go with external hdd connectors because they are meant to be run on 12V. This is what I am doing but that is because I already had some external hddâs. Although with the amount of those drives that have been shucked I imagine there are plenty of Chia farmers who have a bunch of those USB connectors lying around that you might snap up on the cheap.
[PCIe 6pin to 6x 12V jack]([Buy Products Online from China Wholesalers at Aliexpress.com](https://PCIe 6-pin to 6x 12v jack))
My comfort zone would be using this:
PSU to 2x molex
each of the 2 molex to 4xsata
I guess you could push it to 10 or even 15 disk on one connector but thatâs seriously pushing you luck imho.
Peripheral connector on the PSU only has one 12V pin, with a max of 11Amps for the connector and wire.
That gives a max of 132 Watts on 12V
So if you connect 15 disks, that would mean they cannot exceed 8.8 Watts@12V average.
But given that you have 5 peripheral connectors and a max of 30 disks anyway, there is no need to connect that many on one chain anyway.
edit: @enderTown care to weight in ? you have a lot of real world data about this I believe
Looking for him for a long time!
I am considering this for MOLEX/SATA cables.
156W per cable. Hope to connect 10-15 drives on each of the 5 cables. Probably with disk staggering.
endertown is using server PSUs with custom cabling, I am not sure he can help in my case. But anyway, his input has been so valuable to me, I have read again his post i I am planning to âhis wayâ as much as I can.
@AlexXXL you donât want to be running that many drive on your PSU. You want to use half the PSU for better efficiency and to give room because HDD use a lot more power to start than to spin idle. Get a cheap coupler and add one PSU. Believe us, weâve been there. Best case scenario your rig doesnât startup, worst case scenario you fry it and the drives connected to it !
FYI, I have connected 40 drives just to test the PSU and it works like charm, nothing problematic here. I will try 50 and 60 later and measure the power draw. For now, it is around 180W. Like 4.5 W per drive. Which Is quite as expected. I should mention that all 40 drives are connected to LSI RAID cards, meaning that probably disk staggering is in work here.
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Making dumb calculations for ~10 sec startup, the power usage during that time (without staggering): 20 W * 40 drives = 800 W - what is well below your 1.2 kW. Using that dumb calculation, you should be able to run about 55-60 drives.
However, take a look at those two pages below. The first is a nice writeup about power usage during the startup phase for 45 HDs setup. The second are specs for those boxes. All those boxes are meant to run those drives 24/7 for years without degradation (other than HDs) and potentially heavy disks read/writes.
They use 850 W PSU for up to 45 drives (therefore, the above is a âdumbâ calculation). (It may be that they also use that PSU to drive 60 HD boxes - I am not clear on that one.) Those boxes have full staggering support during the startup process. However, it looks like there may be no harm to run those boxes without staggering - again on those 850 W PSUs (if someone without understanding will mess up the setup). Assuming that the main board with everything on it draws ~100-200 W, that implies that you need roughly 650-750 W per 45-60 drives.
What kind of hdd do you have btw?
180W is with all the drives spinning/doing reading or something?
I was just checking some enterprise hdd specs and power consumptions are much lower than I remembered
Still 4.5W sounds like idle consumption
Hey all, I havenât read through this whole thread yet, but I can answer some direct questions at least!
For power connectors, I have one âchainâ type power connector (1 input and 4 outputs along the length of the wire) that is directly wired from the PSU using the 12v-5v converters that I mention in my thread. Then this chain connector plugs into another chain connector, taking up one of the outputs on the original chain. This give me 7 outputs. Now six of those outputs has a Y-splitter out of that, for 12 outputs. So each chain powers 12 disks. I measured voltage at the end of the âchainâ and it stays above 12v and 5v, so that tells me that resistance levels are fine.
Thank you! Thatâs very kind and Iâm glad my posts have helped!
THIS IS ALL EXCELLENT ADVICE!!!
There is a reason that enterprise JBODs run dual 700w power supplies for 12 disks, for example. Of course the main reason for dual supplies is redundancy, and we arenât as concerned about that running Chia although it is nice.
So why 700w to run just 12 disks? Because as the wise authors above have mentioned, power supplies operate at peak efficiency at around 50-60% use. Go higher and it will work, but they will run hotter, less efficient and will probably have shorter lifespans. It actually isnât for startup power - these JBOD are smart enough to stagger their disk power-ups so there isnât a spike in usage. Also keep in mind that these datacenter JBODs arenât just going to waste power - they are on some of the strictest power budgets out there because they spend their lives in datacenters where every watt counts.
I have personally lived this experience. I originally said that my plan was to run 50 drives on a 1200w power supply, but my experience has shown me that this is not enough. Not just for startup power, but ongoing idle power. Iâve had strange disconnections from random drives in my array and only when I add more power do they stop happening. Iâll be updating my other long post soon with some recent findings and an exciting newâŚpivotâŚin my farm. 
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Please look at the graph for the power efficiency. The difference is 3%. Not worth all the talks about it.
SilverStone Technology Co., Ltd. (silverstonetek.com)
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Thatâs very cool, thanks for the link. Lots of good info there verifying what others have said on this thread.
Also consider that it isnât just about efficiency - it is also about voltages. My server PSUs are plugged into a PCIe breakout board with a little voltage meter on it, so I can watch the voltage drop as I add drives. It usually starts out around 12.4v with no drives powered on. With all 50 drives plugged in, it drops to ~12.1v and the ends of my connectors read right at 12v and 5v. That isnât enough room for error in my opinion. If several drives on one connection spike (maybe doing a big write of plot files) then they could drop below 12v/5v and thatâs what I suspect was happening with my random disconnects.
With 20-25 drives, voltage reads 12.3v and ends of wires read 12.1v-12.2v. This seems to be the sweet spot for my 1200w power supplies. YMMV of course! Donât take anybodyâs word for it - wire it up and take measurements!!
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