Why would I get a split rail PSU if it offers less 12V amps?

zalor

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Titles says it all. I'm looking at the OCZ ModXStream Pro 600W (split rail) and CORSAIR Enthusiast Series CMPSU-650TX 650W (single rail) on Newegg and I'm stumped. It says that the Corsair provides 52 amps on the 12V rail and the OCZ offers 25 amps on each of the two 12V rails. Why would I want a split rail design if it's going to provide less amps? I can only use one of the 12V rails (8-pin or 4-pin) on my MOBO. aren't more amps better?
 
It costs more to build a psu with a large single rail than it does 2 smaller rails, which is why cheaper psu's tend to have multiple rails.

I prefer a single large rail, as do most, but some will argue it makes no difference. I'd go with the Corsair because of the single rail and better warranty.

Also 2x 25a rails does not mean it has 50a, it's less than that. You don't just add up the rails it doesnt work that way.

If your going to get a TX, get the TX650 V2, not the regular TX.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139020&cm_sp=Cat_Power_Supplies-_-Spotlight-_-17-139-020

$59.99 after promo code and rebate
 
More amps on the 12V rail is only good up to a certain point...if amps on the 12V rail was the only important thing, then everyone would buy 1000W PSUs.

What are your system specs? A couple of notes on the PSUs you listed:
1. Between the two PSUs you listed, the Corsair is the better quality PSU.
2. Although the OCZ has two 25A rails it can only provide a combined maximum of 504W on the two rails...and that is 42A. The rails are designed like that so the rail is not a limiting factor for components.
 

larkspur

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See: http://www.jonnyguru.com/forums/showthread.php?t=3990

The takeaway: Split rail PSUs aren't necessarily any better than single rail PSUs. Buying a known-quality PSU with a combined +12v adequate amperage is much more important. If the +12v rails are split, add them up to determine whether you have enough +12v amps.

It is easy to see from the price that the Corsair (Seasonic-made) you listed is a higher-quality PSU which I would definitely recommend over the OCZ.
 

Not true...all you have to do is look at the OCZ 600W it has two 12V rails that can handle 25A each, but have a combined maximum rating of 504W and that is 42A.
 

willard

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Single rail PSUs tend to be of higher quality. Lots of lower end PSUs advertise the high number of rails as if it were beneficial, when it is not (and a large number of rails tends to be a bad thing).

As long as your rails have adequate amperage, you're fine. Total amperage on the 12v rails is what determines how much power your big components can draw, which is the bottom line. Who cares if your PSU is 650W if you only get a total of 30A on the 12v rails (yes, I have seen PSUs that bad).
 

djscribbles

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+1 to all the above. Go with the single rail design. Even if split rail was of the same level of quality, you will have to be sure you don't overload either of the rails in the split rail design, if you get to heavy of a load on either one (which usually there is no way to tell which plugs go to which rail) you will have issues.
 
Why are you comparing two power supplies, each with a different power capacity, and expecting the +12V rail capacity to be the same?

It is the combined +12 Volt continuous power rating in relationship to the PSU's total continuous power capacity that is important.

The old Corsair Enthusiast Series TX650 (CMPSU-650TX) has a +12 Volt continuous current rating of 52 Amps. That's 96% of the PSU's capacity.

The OCZ ModXStream Pro Series 600W (OCZ600MXSP) has a +12 Volt continuous current rating of 42 Amps. That's only 84% of the PSU's capacity.

The Corsair CMPSU-650TX PSU is the better PSU for a modern system using a high power draw CPU and discrete graphics card(s) since those are the devices that draw the majority of the power.

If you really want a multiple +12V rail PSU there are some with a better +12 Volt continuous current rating than the OCZ ModXStream Pro Series models. Some of the Antec TruePower models (e.g. TP-650) come to mind.

Safety is one reason to go with a properly designed real multiple +12V rail PSU.
 


Wrong. You can't add them up, it doesn't work that way.
 

zalor

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I'm not.

Why would anybody buy a split rail design if they're worse? When would you ever need two 12V rails instead of one?



I didn't notice any difference between them. Is there a reason to get the V2 other than the price?
 
Why would anybody buy a split rail design if they're worse? When would you ever need two 12V rails instead of one?

Because a good quality multi rail PSU isn't necessarily worse. The generally accepted reason for more than one rail is better stability, but that's a debatable subject when compared to a good quality single rail unit.
 

willard

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The same reason people buy video cards other than the GTX 690. Because you don't always need the best, and price is a factor.
 

zalor

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Here's what I'm stumped on. You buy a split design rail with a 4-pin and 8-pin connector, you hook up the 8-pin connector to your Motherboard, and what do you do with the second one? It just seems completely worthless to have that extra rail dangling around inside your case sucking up half of the amps it isn't even using.
 


Not sure I understand what you're saying there. Do you mean only using one 4 pin connector instead both of the 4 pin connectors (for the total of 8 pin)? Explain.

You may mean the 8 pin (CPU power) plus the 20+4 pin (mobo power), but those are COMPLETELY different.

Usually, yes the CPU is on its own rail in a dual rail unit, but those aren't wasted Amps. The two things that draw the most power in a computer are CPU and GPU.
 


What do you consider "typical"? I know my relatively low end Z68 board has an 8 pin CPU connector (It'll work with just the normal 4 pin 12V, I believe, but it DOES have the extra 4 (the EPS 12V), which I use, since I OC).
 


Alright, got ya. It certainly makes sense, but my thought process is that a lot of "typical" single CPU boards have the full 8 pin connector (although I was fairly certain that 4 was enough for a non-OC situation).
 

Yes, I prefer the humorous side though



I want to expand on this a little, hope you don't mind.

The labeled ratings are a lie, go figure even Antec is using liar labels
The OCP trip point is set at 40 amps for each of the 12v rails


For anyone else that wants to learn about multiple rails and why they are not an issue
http://www.jonnyguru.com/forums/showpost.php?p=37485&postcount=1
 

zalor

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On that OCZ PSU I mentioned it says it has an 8-pin connector, a 4-pin connector and, just for clarity, obviously the 24-pin connector for the mobo power. If my mobo requires the 8-pin connector, what does the 4-pin connector that I'm not using do? Or am I reading it wrong and it doesn't have a separate 4 and 8-pin connector?
 


At least you came back and posted something constructive and instructive. Constructive criticism and supplying good information is ok. Saying you were laughing at everyone that posted before you earlier because they were ignorant of the facts isn't. Being nice goes a long way...
 


The way it's described is a bit confusing, but it doesn't actually mean that the extra 12V CPU connector (EPS 12V) is 8 pin. It's just saying that it's another 4 pin for use in an 8 pin config. There are 2 4 pin connectors total.
 

zalor

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Ooh ok. That's kinda weird but it makes sense now. Thanks for clearing that up for me and everybody else for all the help.
 

OCZ's own documentation shows that there is a 4-pin ATX12V CPU power connector cable and an 8-pin EPS12V CPU power connector cable.

There is no (4+4)-pin CPU power connector on the ModXStream Pro Series.

Look at Hardware Secrets review of the OCZ600MXSP for pictures showing the hardwired cables.

OCZ ModXStream Pro Series 600W (OCZ600MXSP)

+12V1: The cables that are permanently attached (i.e. hardwired) to the power supply
• 1 x (20+4)-pin ATX
• 1 x 8-pin CPU
• 1 x 4-pin CPU

+12V2: The cables for the modular cabling system
• 1 x 6-pin PCI-E
• 1 x (6+2)-pin PCI-E
• 4 x Peripheral
• 2 x Floppy
• 6 x SATA