I read somewhere that it's very important to use a single +12V rail design when choosing a power supply. Does that mean that the power supply must have only 1 12V Rail listed in the specs?

 

Also, can anyone explain why the power supply has to have a single +12V Rail? One would think, "the more, the better"

 

Thanks

Sometimes power supplies that are listed as multi rail are actually single rail. I have one like that. I opened it up and found all the 12 volt lines hooked together. The early ATX (Intel) spec required separate rails. Good history on that at silentpcreview.

 

Multiple rails will typically split their power, sending a lot of their power to PCIe plugs for high powered video cards and the motherboard to power fast processors. An unRAID server needs 80-90 percent of it's 12 volt current to be provided to the hard drives. If the Molex and SATA connectors only provide 25 percent of the power to those connectors, the hard drives may have inadequate starting current (about 1.5-2.5 amps per drive on the 12 volt rail).

 

It is wise to use a recommended powersupply. I love the Corsair 650TX (made by Seasonic). It is efficient, cost effective (if you get it on sale) and reliable. I personally don't want a modular power supply. I just hack off the lines I don't need. One less connector to go bad.

I read somewhere that it's very important to use a single +12V rail design when choosing a power supply. Does that mean that the power supply must have only 1 12V Rail listed in the specs?

 

Also, can anyone explain why the power supply has to have a single +12V Rail? One would think, "the more, the better"

 

Thanks

Easy... it is because only one of the potential 12 volt rails will likely be connect to the molex and sata connectors.  Usually it is limited to 18 Amps capacity and very frequently it also will be the same rail powering the 24 pin motherboard connector.  In effect you might have only 12 to 15 Amps really available for the disk drives and fans.  The other 12 volt rails and their potential capacity will be reserved for use for PCIe video cards and cpu power.  This can make an expensive 650 Watt multi-rail supply less capable than an inexpensive 300 watt supply.

So when I look at PSU specs, it should say

 

+12V Rails: 1

 

Correct?

So when I look at PSU specs, it should say

 

+12V Rails: 1

 

Correct?

Correct

I think on Newegg you can even set that as a search parameter.

You need look no further than Corsair, Seasonic, and Antec Neo Eco.  There are others, but these are the best and often the cheapest.

Just for reference, here's a link to a Newegg search for all Power Supplies with a Single +12V Rail of either Corsair, Seasonic, or Antec brands sorted by lowest price

Any opinions on the OCZ StealthXStream2 400W? I can't tell if it's a single rail or not, either.

 

Thanks

 

Any opinions on the OCZ StealthXStream2 400W? I can't tell if it's a single rail or not, either.

 

Thanks

 

Manual is here: http://www.ocztechnology.com/res_old/manuals/stealthxstream_400W_manual.pdf

 

12V1 SATA Connector

12V1 Main 24 pin motherboard connector

12V1 PCI Express connector

12V1 Molex Connector

12V1 floppy Disk connector

 

12V2 4-pin CPU Power connector

 

So... The molex and sata connectors share the 12v1 supply with the motherboard.   The 12v2 supply is entirely used by the CPU.

 

12v1 is rated at 17 Amps, but you are sharing it with the motherboard, memory, fans.   I'm guessing you have less than 15 Amps available possibly less.

12 volts * 15 Amps gives you the equivalent of a single rail 180 watt supply.  Probably stressed out with more than 4 or 5 disks.

 

Keep looking... unless you are doing a 3 disk basic array, it is not a good match.

 

Ocz is one of the few manufacturer that has the 12 volt rail distribution in their documentation.  Many of the others leave you guessing.

 

Joe L.

Thank you so much, Joe! I'll keep looking.