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Multi-rail psu, how does that work?

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August 14, 2009 3:51:57 AM

Ok, So I'm looking at a psu, and it has 6 12v rails, 4 @ 20a and 2 @ 35a. I'm also looking at getting the EVGA gtx 295 co-op edition. The website says that card requires a min 650 watt psu, pulling 46a of 12v power. My question is, would my card be connected to just one of those rails? If so, wouldn't that mean that the PSU wouldnt power the card? Would I need to find a PSU that offers a 12v rail @ 46a to power my card? I have no Idea how these multi rail PSU's work. Any advice would be much appreciated.

More about : multi rail psu work

August 14, 2009 4:42:34 AM

Single rail multi rail who gives a sh*t.
August 14, 2009 4:57:17 AM

bpogdowz said:
Single rail multi rail who gives a sh*t.

It's not that I have a preference on single rail or multi-rail, what I'm concerned with is does the multi-rail psu that I'm looking at have the power to run my card, or would I have to get a psu that has at least one rail with at least 46a on it, or is the amperage on all the different rails sufficient? In other words, do I need to look at each rail's individual amperage, or do I need to look at the amperage that all the rails add up to? Most cards today have a six pin and an eight pin connector, so I'm thinking that as long as two of the rail's amperage equals 46a or more, I would be ok. I just need confirmation before I buy a PSU that won't work.
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August 14, 2009 5:10:13 AM

I believe it draws from multiple rails if required, but keep in mind that the card is not saying it will pull 46 amps, just that it recommends 46 amps for any full system you put it into.

On that note, however, having 6 rails seems pretty unusual and possibly suspect. If you tell us exactly what model you are looking at, we can probably tell you if it's a good one or offer a better alternative.
August 14, 2009 5:18:14 AM

spinny said:
I believe it draws from multiple rails if required, but keep in mind that the card is not saying it will pull 46 amps, just that it recommends 46 amps for any full system you put it into.

On that note, however, having 6 rails seems pretty unusual and possibly suspect. If you tell us exactly what model you are looking at, we can probably tell you if it's a good one or offer a better alternative.



ok cool. I'm looking at the Kingwin Mach 1 Modular 1220w PSU. I used the antec Power supply calculator (located here - http://www.antec.outervision.com/PSUEngine ) and it said my system would end up drawing about 1080 watts under some load, So I decided that 1200w would be enough. Also, here is a link to the PSU I'm looking at if you wanna review the full specs to help me out with my question - http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4256916&sku=K450-2505
August 14, 2009 5:20:29 AM

grouchpunk08 said:
It's not that I have a preference on single rail or multi-rail, what I'm concerned with is does the multi-rail psu that I'm looking at have the power to run my card, or would I have to get a psu that has at least one rail with at least 46a on it, or is the amperage on all the different rails sufficient? In other words, do I need to look at each rail's individual amperage, or do I need to look at the amperage that all the rails add up to? Most cards today have a six pin and an eight pin connector, so I'm thinking that as long as two of the rail's amperage equals 46a or more, I would be ok. I just need confirmation before I buy a PSU that won't work.


Yeah it runs your card all day and all night.
August 14, 2009 5:33:50 AM

Ok now I want to know exactly what kind of system you are building here LOL.

I put in a dual socket i7 975 extreme overclocked to 4.5GHz at 100% load, SLI GTX 295s, 5 hard drives, 2 optical drives, 2 PCI cards, 10 USB devices, 5 250mm fans and dual water pumps and still only came out to 994 watts.

Which is to say that you either a) did something wrong in this calculator or b) are building an extremely serious system packed with hardware in which case PSU recommendation may change.
August 14, 2009 5:50:41 AM

spinny said:
Ok now I want to know exactly what kind of system you are building here LOL.

I put in a dual socket i7 975 extreme overclocked to 4.5GHz at 100% load, SLI GTX 295s, 5 hard drives, 2 optical drives, 2 PCI cards, 10 USB devices, 5 250mm fans and dual water pumps and still only came out to 994 watts.

Which is to say that you either a) did something wrong in this calculator or b) are building an extremely serious system packed with hardware in which case PSU recommendation may change.

Thats odd, HEre is my hardware -
EVGA x58 SLI LE
Intel Core I7 920 2.66 GHZ
EVGA GeForce GTX 295 Co-op Edition
12 Gigs Corsair DDR3 1333 MHZ - 6x 2gb Sticks
1 TB HDD
DVD DRive
PCI Wireless Card

And this is what I put into the options on the calc.
Single Socket
Highend Desktop MOBO
Intel Core I7 920 @ 100% Utilization/ No overclock
6 Sticks DDR3 SDRAM
GEFORCE GTX 295 with SLI option- for future expansion possibility
1 SATA HD
1 DVD-RW/DVD+RW
2 Zip Drives
PCI Nic
10 USB Devices/2 Firewire devices - won't use all those at the start, but for future expansion
Fan Controller
Front Bay Card Reader
5 140mm Fans
System Load 100%
Capacitor aging at 35% - would like to use this PSU for over a year by the chance it doesnt crap out a few months in
a b ) Power supply
August 14, 2009 5:59:18 AM

grouchpunk08 said:
The website says that card requires a min 650 watt psu, pulling 46a of 12v power. My question is, would my card be connected to just one of those rails? If so, wouldn't that mean that the PSU wouldnt power the card? Would I need to find a PSU that offers a 12v rail @ 46a to power my card?

The 650W/46A is a recommendation and not a requirement. It is also not a single rail recommendation, nor is it for the video card alone but the entire system.
a b ) Power supply
August 14, 2009 6:00:28 AM

spinny said:
I believe it draws from multiple rails if required

The connector attached to the card can only draw power from the rail to which it is attached.
August 14, 2009 6:03:35 AM

theAnimal said:
The 650W/46A is a recommendation and not a requirement. It is also not a single rail recommendation, nor is it for the video card alone but the entire system.

Thanks, thats good to know. This will be my first build, and I guess you don't know these types of things until you ask someone.
a b ) Power supply
August 14, 2009 6:04:11 AM

grouchpunk08 said:
GEFORCE GTX 295 with SLI option- for future expansion possibility

That would be why it recommended a 1080W PSU.

Unless you're actually planning to add a second GTX295 (which does not scale well BTW), a good quality 650W+ PSU is plenty. I'd suggest the Corsair HX750.
August 14, 2009 6:11:16 AM

theAnimal said:
That would be why it recommended a 1080W PSU.

Unless you're actually planning to add a second GTX295 (which does not scale well BTW), a good quality 650W+ PSU is plenty. I'd suggest the Corsair HX750.

I understand that these calculators arent always exactly accurate, but when I take out the SLI option, it tells me I'd need 837 Watts. If thats the case, then a 1000w psu would be the way to go, correct? And if 1000 Watts is what I need, I had been looking at the Corsair 1000hx PSU. Anyone know if thats good quality/reliable?
August 14, 2009 7:02:51 AM

The Corsair 1000HX is an amazing PSU, and is absolutely rock solid. I have one powering my system (3 hard drives, 2 4870x2s, overclocked i7, 12 gigs of RAM, etc), and it doesn't even have to ramp the fan up at full load. It's a great choice, and I highly recommend it.

That having been said, you'd be fine with an 850TX or 750HX if you don't add a second 295. Regardless of what the PSU calculator says, that setup wouldn't draw more than 650 watts, tops.
August 14, 2009 7:06:18 AM

cjl said:
The Corsair 1000HX is an amazing PSU, and is absolutely rock solid. I have one powering my system (3 hard drives, 2 4870x2s, overclocked i7, 12 gigs of RAM, etc), and it doesn't even have to ramp the fan up at full load. It's a great choice, and I highly recommend it.

That having been said, you'd be fine with an 850TX or 750HX if you don't add a second 295. Regardless of what the PSU calculator says, that setup wouldn't draw more than 650 watts, tops.

Ok, thanks for the info man. I'll prolly go with the Corsair 1000hx, just to have some wiggle room if I decide to go with the SLI in the future.
a c 144 ) Power supply
August 14, 2009 3:27:53 PM

Corsair's are excellent PSU's. They are very conservatively designed - enough that they can produce about 120% of their rated power throughout their entire line.
August 14, 2009 7:38:24 PM

Ok, yeah I went to the Corsair website, it also has a calculator type deal, and It asks for processor, gfx card and number of cards, and number of hard drives. I put that in and It suggested the 1000hx, because I put a 2 for number of cards and hdd's, for future expansion possibility without having to get a new PSU if I needed more power. And you guys seem to know what your talking about, and you say my current build list wont draw as much as I previously thought it might. I am definitely thinking about the Corsair 1000hx. Thanks for all your help guys.
a c 144 ) Power supply
August 15, 2009 4:15:25 PM

Case in point: I have a couple of Antec TP3's - a 550 watt (42 amps total @ 12 volts) and a 650 watt (52 amps total @ 12 volts). I was curious about the whole multiple rail thing. So I did some investigating. First I measured a dead short between any two yellow wires (12 volt lines) - main power, EPS, PCI-e; it didn't matter. I opened the PSU's. Each had a cluster of three "different" 12 volt points (12V1, 2, and 3). All three were tied together.

Both have been good, solid, reliable PSU's. I also have a Corsair TX750 (single 60 amp rail). It's been running less than a year, so I cannot tell about long term reliability.
a b ) Power supply
August 17, 2009 1:36:52 PM

Multiple Rail Power Supply is excellent for Load Management and distribution. That is if you know how much each of your HW consume and its behavior(Know or undertand your load).

Load isolation and distribution results to better stability as one is not affected by the other. Less un-explained hang-ups or system crash.

With that information i use Multi-rail system against a single one big rail PS (i.e. 12V 70AMP)...



As good rule of thumb its good to isolate different loads:
1) Video Card: Has the biggest current fluctuation on different conditions:
---- Current Surge at Power- Up. It will draw > 150% of the rated load
---- Current Surge due switching from 3D Games to ordinary office Apps(Vice Versa). You have access to power Plotter you can see swings in volages and increase in noise due to power demand change on the video card as a function of application.

When loaded to a separate sets of rails then the other loads are not affected by the disturbances created by these high current loads.


2) Hard Drives:: Anything that uses MOTORS are source of NOISE. It is what it is and best on its own ISOLATED POWER LINE.
--- Normally stable.... Increase in current draw but not drastic can be observeb when reading large database files.
--- Bigger current fluctuation or changes can be observed when you set your hard drive to stopped the motors when not in used(i.e. sleep mode). Re-starting the motor will create a temporary surge in current.
---- This gete complicated with multiple drives...

ISOLATED LOADS provide protect the loads from fluctuation created or induced by one or combination of loads (i.e. video card or 2 x video card). Protection is in terms of more stable voltages and reduction of electrical noise. Electrical noise is less likely to transfer to another rail( Or the transfer of noise is reduced if not eliminated).

3) Know and or define your loads.... Then indentify your power supply....AVOID UNKNOWN CHEAP BRANDS.

Note:
VIRTUAL SHORT DEVICES:
Power Supply Drivers/Regulators are LOW IMPEDANCE DEVICES.... ~ very close to ground. These are called VIRTUAL SHORT DEVICES or CIRCUITS. It does not mean that the circuit is shorted or physically connected.

Combination of active & passive devices in electronic circuits complicates METER READINGS...


Need to understand what the digital meter is telling...

This is perfectly normal and can be explained Mathematically and verified in actual circuits in the LABS.


RMS MEASUREMENTS:
Common Digital Meters will provide you RMS measurements. The others will provide MAX/Min features. In reality these meter are not capable in providing the actual real-time fluctuation of current or voltage.

You need curve traces, plotters, high speed real-time scope, pulse/noise detectors to capture the actual behavior of supply current and voltages at different condition. These parameters change in microseconds or even less.
!