Side question re single vs. multi rail

[Ken B.]

OK, so I just read Oklahoma Wolf's sticky regarding single vs multi rail PSUs. I also just got an Antec TruePower New 650 Watt. Pertinent part for me is...

Is it true that some PSU's that claim to be multiple +12V rails don't have the +12V rail split at all?

Yes, this is true. But it's the exception and not the norm. It's typically seen in Seasonic built units (like the Corsair HX and Antec True Power Trio.) It's actually cheaper to make a single +12V rail PSU because you forego all of the components used in splitting up and limiting each rail and this may be one reason some OEM's will not split the rails, but say they are split. Some system builders adhere very closely to ATX12V specification for liability reasons, so a company that wants to get that business but also save money and reduce R&D costs will often "fib" and say the PSU has it's +12V split when it does not.

Why don't those PSU companies get in trouble? Because Intel actually lifted the split +12V rail requirement from spec, but they didn't actually "announce" it. They just changed the verbiage from "required" to "recommended" leaving system builders a bit confused as to what the specification really is.

OK, So this Antec I got says it has four 12v rails. I mean personally, I don't really care, it's got plenty of power for my use no matter what. But I like to think of myself as a reasonably informed consumer.

So, according to above quote, this "four 12v rails" claim is a straight out lie?!

Antec is using a a single large 12V rail, but is just saying it's split for marketing reasons? But then how does that jibe with gamers "in the know" about a single large 12V rail usually being best? I mean, it's pretty obvious this PSU is marketed towards gamers. I guess I do not understand Antec's thinking, here.

 

[Ach3r0n]

Split rails were initially used as a safety concern as far as I recall. They were afraid some idiot would fry himself.

Anyway, it is true. Split rails are often not really split. This was mentioned in a couple of the reviews of the Corsair 620W I picked up a couple weeks ago.

 

[Oklahoma Wolf]

OK, so I just read Oklahoma Wolf's sticky

You're crediting the wrong guy

So, according to above quote, this "four 12v rails" claim is a straight out lie?!

No... if you exceed the point where the individual OCP is set, the unit will shut down. It's like the circuit breakers in your house... just because all the 12V rails come from the same source, it doesn't mean there aren't effectively four separate circuits.

Split rails were initially used as a safety concern as far as I recall. They were afraid some idiot would fry himself.

No, they were worried the unit wouldn't shut down properly in the presence of a short circuit and start a fire or damage hardware. And they had a valid point there... some single 12V units on the market right now are so powerful, you can tap a 12V wire to bare metal and in some cases it will not shut down just because the OCP is set significantly higher than the current draw presented by that momentary short circuit.

The Corsair you cited is a special case... it was always a single 12V design. They just didn't change it to be such until after all their boxes and marketing stuff had been done up, and the unit already filed with the UL. It saved them a pile of money to keep calling them triple 12V when in reality the individual OCP had been removed and they were effectively single 12V units.