Enermax Dxx 1000W rail question.

[The_Blood_Raven]

Ok I am looking for a new PSU and was set on the PC P&C 750w silencer or the 1000w PSU. I liked the single rail, and what I have heard is that the single rail is THE best design. Then one day I stumbled upon Enermax Galaxy when I was looking at Antec 900 mods in a previous post. All I have read about the PSU is that its THE high end PSU on the market, or atleast way up there. This confuses me, because it says it has 5 rails, and a reviewer (http://www.guru3d.com/article/content/429/) said that was a huge plus. I am terribly confused by this because all I read said the single rail design was the best hands down. Can somone PLEASE explain this to me, and give me your opinions on this PSU.

Thank you for your time and effort.

 

[WR2]

(1) Single Rail PSU
(2) Multiple "current limited" 12 volt rails derived from single rail PSU
(3) Multiple independent 12 volt rails PSU

Because of an ATX power specification that says:
- 3.2.4. Power Limit / Hazardous Energy Levels-- Under normal or overload conditions, no output shall continuously provide more than 240 VA under any conditions of load including output short circuit, per the requirement of UL 1950/ CSA 950/ EN 60950/ IEC 950. (ATX12V Power Supply Design Guide, version 2.2)
many PSU are designed to stay within that spec. That means that each 12v rail can deliver only 20Amps of power or 240Watts.

(1) There are some PSU that ignore that spec and output all +12V on a single rail
(2) Most multi-rail PSUs are using a single rail and splitting it with current limiters to multiple 20amp (or less) "rails". (Single 12V transformer with common ground)
(3) Rarest of all is a PSU with true multiple independent 12volt rails.

The main problem of type 2 "current limited" 12 volt rails is that if you try and draw above 240VA you run the risk of the PSU shutting down. To avoid that you need to make sure you "load balance" the power being drawn over the multiple rails to ensure that no single rail is sucking more than 20amps. If you have an 18amp rail its more likely an actual 20amp limit, and I've heard that many PSUs allow more than 20amp draw before the limiter kicks in and shuts the PSU down. Usually this is not a problem since most people wildly over estimate how large a power supply they actually need and so load balancing never becomes a real issue. Since single rail PSU do away with the need to "load balance" they can be easier to use with a very high power requirement.

[:wr2:2] IMO it's probably more important to get a PSU with excellent design, high quality parts, above average build quality and superior electrical performance (stability of the output voltages, low ripple at peak loads, etc.,) than to worry about the single rail/multi-rail issue.

 

[WR2]

I found a Enermax EGA1000EWL review I liked over at HardwareLogic
The review had a nice chart that showed the protection circut ratings. Note that some of the +12V rails had a trigger range well over 20Amps.

That review also explained that the Galaxy:
"Meets 2007 EPS12V specification for next-generation systems
The new revision requires a fifth 12V rail to keep high end systems stable and allows TRIPLE-QUAD + 24 support (single, dual, and quad CPUS and GPUS, as well as up to 24 drives)"

Another review @ SilentPC Review
The Hardware Logic review also had links to reviews at Guru3D.com and ProClockers.com

In this PC P&C 750 review it mentions how PC P&C describes the advantages/disadvantages of single/multi rails.
LegitReviews.com