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Single rail PSU recommendation

J

Jeroen1000

Limp Gawd
Joined
Sep 17, 2010
Messages
266
I already have a serious headache figuring this out.

If I understand correctly, multi-rail PSU's used in non-server grade computers just have a 20 ampére current limiter on each rail. I call them 'single rail PSU's with a twist': they only have one rail but somehow they split this one rail into multiple rails which each have their own current limiter.

A true multirail PSU would have multiple transformers with as many current limiters as there are transformers.


A single rail PSU has just one current limiter which will kick in if you exceed it's maximum rated ampérage. Long story short, single rail PSU's are just easier to deal with if you have to provide startup current for an armada of hard disks.

I just don't understand how they can get away with it. Didn't safety standards dictate that 20 amps is the max a rail is allowed to offer?

Anyway, which brands have what I'm looking for?
 
Your interpretation is mostly correct. A "true" multi-rail PSU doesn't need independent sources for each rail. Over-current protection on each rail is enough for a PSU to be called a true multi-rail unit, since a rail is just a power source with a fixed current limit.

Safety standards don't require the limit to be 20A. There used to be a similar requirement in the ATX specification, but it was removed a few years ago. A 30-40A OCP limit is generally enough to ensure safety. Anyway, it's true that in certain situations a PSU without OCP or with an OCP limit that is too high can cause a fire, but the likelihood of running into a situation like that is very low. In general, safety isn't something you need to worry about with single or multi-rail PSUs, though in theory, multi-rail PSUs are safer.

To tell you which brands have what you're looking for, you're going to have to actually say what you're looking for.
 
Yes, actually forgot to say what I was after.:)

I'm guessing somewhere between 550 and 650 watts (it needs to cope with 20 HD's startup current + 1 OS HD if I can't get staggered spin up to work). CPU will most likely be an Athlon x4 (95W TDP). 2 times 4 GB RAM, 1 Areca RAID-controller (1680i), 1 slimline CD-ROM and a seperate dual NIC ethernet card.

I'm using AMD's integrated GPU so no power hungry GPU.

The sad thing is my system will mostly be idle. I'd need perhaps 380W if I can spin up the HDD sequentially. But if I can't my system might be toast so I might as well err on the side of caution.
 
I'd look for a decent ~500W PSU if I were you. Antec NEO ECO, Seasonic S12II, etc.
 
Most are dual 12v. No one likes to advertise with powerful single rail so it seems.
 
Both of the units I mentioned are single-rail. Most units in the 500W range are as well.
 
Absolutely wrong about multi-rail psus now. There were old protection rules regarding 20A long ago. These days most psu makers go way above 20A. Like the Antec HCP-1200 has ocp limits of 30A on it's 8 rails. While the lower power HCP's have OCP at 40a on each of it's 4 rails. Good luck getting over that limit, there aren't enough connectors on each rail to get over unless you're doing something insane. Single rail vs multi-rail does not matter whatsoever now unless you're buying a junk psu.
 
Zero82z said:
I'd look for a decent ~500W PSU if I were you. Antec NEO ECO, Seasonic S12II, etc.
Click to expand...

For 20 hard drives, a 500W PSU really? I would aim at least a little higher and go for a 650W PSU like the Corsair 650TX or even the 620W versions of the PSUs you mentioned.
 
Danny Bui said:
For 20 hard drives, a 500W PSU really? I would aim at least a little higher and go for a 650W PSU like the Corsair 650TX or even the 620W versions of the PSUs you mentioned.
Click to expand...
If he can get staggered spinup to work, then 500W would be plenty, and even if he can't, a quality 500W PSU should be able to handle the inrush spike for long enough providing it isn't high enough to trigger the OCP.
 
Zero82z said:
If he can get staggered spinup to work, then 500W would be plenty, and even if he can't, a quality 500W PSU should be able to handle the inrush spike for long enough providing it isn't high enough to trigger the OCP.
Click to expand...

Allright then
 
Yeah, I've been reading some reviews and the mutli rail PSU's (2 rails or more) seem to allow 40 amps on any rail before engaging the OVP. The 20 amps limit is bogus (at least with new modern PSU's). Obviously, you should not be able to exceed the total amp rating for 12V.

A review on hardware secrets indicates my Enermax PRO82+ 525 W does not engage the OVP even when you draw 33 amps (the maximum their load tester can draw) while each rail is rated at 25 amps according to the label.

I hope to find a test where they load several 12 V rails to 33 amps.

edit: this PSU-looks nice although expensive: http://www.hardwaresecrets.com/article/Seasonic-X-Series-560-W-Power-Supply-Review/1118/6
 
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You would need to give some facts or experiences. I've decided on the Seasonic cause I can plug in more molex cables when needed, it will allow up to 46A start up current and most likely is overspecced (can be overloaded safely).

It also has a single 12v rail (meaning its OVP will play nicely). If anything can match this at a lower price, shoot!:)
 
I've been in doubt between the PSU's you suggested and the Seasonic. But the latter one really offers me piece of mind on the label:)

Thanks, I did mean OCP :)
 
Zero82z said:
Did you bother actually reading the whole thread? That PSU is way overkill for this purpose and is significantly more expensive than the one I suggested.
Click to expand...

I did not. just skimmed. but fwiw, if the op wants a real good psu with no worries about what he can upgrade to later. why skimp on the one part that's usually the easiest to transfer from one build to the next. They make the exact same psu in a 750 I think, or smaller. just look around. That's just the one I have and would recommend it. Almost all of silverstones product line is single 12v rail.

edit:
500w: http://www.amazon.com/SilverStone-S...RDUU/ref=sr_1_3?ie=UTF8&qid=1289310633&sr=8-3
650: http://www.amazon.com/SilverStone-D...IOCS/ref=sr_1_5?ie=UTF8&qid=1289310682&sr=8-5
750: http://www.amazon.com/SilverStone-O...AY/ref=sr_1_12?ie=UTF8&qid=1289310716&sr=8-12
 
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I do feel I need to add another post as this is rather important. I went with a Silverstone modular PSU because you could buy a "short cable-set" for it. And these shorter cables were really, really REALLY useful:). Moreover, it was single rail so it ticked all my boxes.

Here is the model number:
SST-ST60F-P
 
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