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Anything wrong with 4-rail PSU's?

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May 29, 2012 3:02:31 PM

I had been focused on finding a single rail PSU in the 650W-850W range.

But I noticed that all of Antec's high-end PSUs in that range have 4 rails.

So I was thinking, should I dismiss them just because they have more than one rail?

Are there any advantages to having multiple rails, such as efficiency, stability etc.?

More about : wrong rail psu

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a c 243 ) Power supply
May 29, 2012 3:07:40 PM
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May 29, 2012 3:14:46 PM

Nothing wrong with them, but you may have problems with SLI/Crossfire. I have 2 GTX 570's which overloaded my multi rail OCZ power supply causing my machine to shutdown.

I now have a single rail and the problem is resolved.
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May 29, 2012 4:01:29 PM



At the end of the article, jonnyguru lists these three important questions. I don't think I've ever seen these specs for any PSU. Where do you find the answers to these questions?


Is the PSU rated at continuous or peak?

What temperature is the PSU rated at? Room (25° to 30°C) or actual operating temperature (40°C to 50°C)

If room temperature, what's the derating curve? As a PSU runs hotter, it's capability to put out power is diminished. If no de-rate can be found, assume that a PSU rated at room temperature may only be able to put out around 75% of it's rated capability once installed in a PC.
a b ) Power supply
May 29, 2012 4:11:08 PM

I had the same problem with the Antec truepower 750 watt in my current rig. The single rail thermaltake I'm using now works well.

Each 25a rail on the Antec should have been able to support a 6770 on it's own, but they didn't.
a c 243 ) Power supply
May 29, 2012 4:31:15 PM

ratsa said:
At the end of the article, jonnyguru lists these three important questions. I don't think I've ever seen these specs for any PSU. Where do you find the answers to these questions?


1. Is the PSU rated at continuous or peak?

2. What temperature is the PSU rated at? Room (25° to 30°C) or actual operating temperature (40°C to 50°C)

3. If room temperature, what's the derating curve? As a PSU runs hotter, it's capability to put out power is diminished. If no de-rate can be found, assume that a PSU rated at room temperature may only be able to put out around 75% of it's rated capability once installed in a PC.

1. On the label
2.Buy a thermometer
3. Need the documentation from the manufacturer
a c 243 ) Power supply
May 29, 2012 4:48:44 PM

quilciri said:
yes it happens, but I RMA'd the first one, and had the same problem with the second.

Don't know what to tell you
I've had no problem running SLI GTX260 or ENGTX460TOP on any of my TP's ( 2x 550w and 2x 750w ), both sets of cards are more power hungry than 3 x 6770's
a b ) Power supply
May 29, 2012 4:54:00 PM

I don't know if the problem was the split 12v or Antec's shoddy workmanship, but why take a chance on either?

Also, there's wasted potential on split rails, as your link points out.

Quote:
So there are no disadvantages to using a PSU with multiple +12V rails?

No! I wouldn't say that at all. To illustrate potential problems, I'll use these two examples:

Example 1:

An FSP Epsilon 700W has ample power for any SLI rig out there, right? But the unit only comes with two PCIe connectors. The two PCIe connectors on the unit are each on their own +12V rail. Each of these rails provides up to 18A which is almost three times more than what a 6-pin PCIe power connector is designed to deliver! What if I want to run a pair of GTX cards? It would have been ideal if they could put two PCIe connectors on each of those rails instead of just one, but instead those with GTX SLI are forced to use Molex to PCIe adapters. Here comes the problem: When you use the Molex to PCIe adapters, you have now added the load from graphics cards onto the rail that's also supplying power to all of your hard drives, optical drives, fans, CCFL's, water pump.. you name it. Suddenly, during a game, the PC shuts down completely.

Solution: To my knowledge, there aren't one-to-two PCIe adapters. Ideally, you'd want to open that PSU up and solder down another pair of PCIe connectors to the rails the existing PCIe connectors are on, but alas... that is not practical. So even if your PSU has MORE than ample power for your next graphics cards upgrade, if it doesn't come with all of the appropriate connectors, it's time to buy another power supply.

Example 2:

Thermo-Electric Coolers (TEC's, aka "Peltiers") take a lot of power and are typically powered by Molex power connectors. I, for one, prefer to run TEC's on their own power supply. But that's not always an option. If you had a power supply with split +12V rails and powered your TEC's with Molexes, you would be putting your TEC's on the same +12V rail as the hard drives, optical drives, fans, CCFL's, water pump.. you name it, just as you did with the Molex to PCIe adapters. The power supply could, essentially, shut down on you in the middle of using it. A power supply with a single, non-split, +12V rail would not have any kind of limit as to how much power is delivered to any particular group of connectors, so one could essentially run several TEC's off of Molex power connectors and not experience any problems if one had a single +12V rail PSU.



Seemingly the only benefit of split rails acc. to that link is safety, but his point confuses me. Splitting the 12v doesn't seem any safer. Even though they can share a 12v, a 6 pin is already limited to 75w (6.25a), and an 8 pin is capped at 150w (12.5a). Where's the overload chance there?
May 29, 2012 5:13:27 PM

The people who like 4 rail PSU's will point out that it's safer because if a rail goes out then it won't have the potential to take everything out with it. The only PSU that I have ever had a problem with was a cheap no name PSU a long time ago. Lesson learned. I only buy Corsair since then.
May 29, 2012 5:20:15 PM

The bottom line, based on everything I've read thanks to everyone's helpful contributions above:

(1) There is no disadvantage to multiple rails so long as each rail has sufficient power for whatever you're hooking it up to;

(2) Multiple rails, if done right, are safer than one; and

(3) There are more important things about a psu than the number of rails, many of which are not published or are hard to find out.

Thanks!
a c 243 ) Power supply
May 29, 2012 5:58:50 PM

ratsa said:
The bottom line, based on everything I've read thanks to everyone's helpful contributions above:

(1) There is no disadvantage to multiple rails so long as each rail has sufficient power for whatever you're hooking it up to;

(2) Multiple rails, if done right, are safer than one; and

(3) There are more important things about a psu than the number of rails, many of which are not published or are hard to find out.

Thanks!

The bottom line is that it doesn't really matter
A good quality single or multi rail psu will serve you well
May 29, 2012 6:01:29 PM

Best answer selected by ratsa.
a c 243 ) Power supply
May 29, 2012 6:06:45 PM

quilciri said:
I don't know if the problem was the split 12v or Antec's shoddy workmanship, but why take a chance on either?

Also, there's wasted potential on split rails, as your link points out.

Quote:
So there are no disadvantages to using a PSU with multiple +12V rails?

No! I wouldn't say that at all. To illustrate potential problems, I'll use these two examples:

Example 1:

An FSP Epsilon 700W has ample power for any SLI rig out there, right? But the unit only comes with two PCIe connectors. The two PCIe connectors on the unit are each on their own +12V rail. Each of these rails provides up to 18A which is almost three times more than what a 6-pin PCIe power connector is designed to deliver! What if I want to run a pair of GTX cards? It would have been ideal if they could put two PCIe connectors on each of those rails instead of just one, but instead those with GTX SLI are forced to use Molex to PCIe adapters. Here comes the problem: When you use the Molex to PCIe adapters, you have now added the load from graphics cards onto the rail that's also supplying power to all of your hard drives, optical drives, fans, CCFL's, water pump.. you name it. Suddenly, during a game, the PC shuts down completely.

Solution: To my knowledge, there aren't one-to-two PCIe adapters. Ideally, you'd want to open that PSU up and solder down another pair of PCIe connectors to the rails the existing PCIe connectors are on, but alas... that is not practical. So even if your PSU has MORE than ample power for your next graphics cards upgrade, if it doesn't come with all of the appropriate connectors, it's time to buy another power supply.

Example 2:

Thermo-Electric Coolers (TEC's, aka "Peltiers") take a lot of power and are typically powered by Molex power connectors. I, for one, prefer to run TEC's on their own power supply. But that's not always an option. If you had a power supply with split +12V rails and powered your TEC's with Molexes, you would be putting your TEC's on the same +12V rail as the hard drives, optical drives, fans, CCFL's, water pump.. you name it, just as you did with the Molex to PCIe adapters. The power supply could, essentially, shut down on you in the middle of using it. A power supply with a single, non-split, +12V rail would not have any kind of limit as to how much power is delivered to any particular group of connectors, so one could essentially run several TEC's off of Molex power connectors and not experience any problems if one had a single +12V rail PSU.



Seemingly the only benefit of split rails acc. to that link is safety, but his point confuses me. Splitting the 12v doesn't seem any safer. Even though they can share a 12v, a 6 pin is already limited to 75w (6.25a), and an 8 pin is capped at 150w (12.5a). Where's the overload chance there?

A 6 pin is limited solely by the specification given to the connector, not by the amount of watts
That's why they can do this

6+2 ( 8 pin ) = 150 watts. + 6pin = 225 watts from 1 set of wires

You're trying to point to 1 example of a poorly designed psu, listed to show the possible pitfalls, to make your point ? Come on
I'm not trying to change your opinion, just make the facts available
a b ) Power supply
May 29, 2012 6:25:16 PM

delluser1 said:
A 6 pin is limited solely by the specification given to the connector, not by the amount of watts
That's why they can do this
http://i1081.photobucket.com/albums/j351/contrvlr/dualpcie.jpg
6+2 ( 8 pin ) = 150 watts. + 6pin = 225 watts from 1 set of wires

You're trying to point to 1 example of a poorly designed psu, listed to show the possible pitfalls, to make your point ? Come on
I'm not trying to change your opinion, just make the facts available


I'm asking a question, not arguing here....

225 watts = 18.75a. I still don't see the overload potential for a single rail here. It seems like you'd have to splice in several more connectors to come close, and who's going to mod a PSU like that?
!