View Full Version : Dual-Rail PSUs Vs Single rail (+12V rail)
Multi-rail PSUs are getting popular but I dont understand how they work. I`m using large single-rail PSUs because I have a Vapochill but I`m wondering why multi-rail PSUs dont work with it.
I know its because the current draw on the +12V rail is too large, but how is the current used in multi-rail PSUs? Is there a way of splitting the power draw across compopnents to balance the load on both rails? (e.g....opticals, HDD, GPU molex on one rail, CPU/mobo on the other)
Does the computer draw current from one rail until its at capacity then start on the 2nd rail, then 3rd until its either used all the rails or taken as much as it needs?
This is bugging me because it seems that my choices are...not limited..but not as wide as I`d like.
Any advice, info welcome. You dont need to hold back on the details, I`m studying engineering so I`ll be able to follow. :)
Another Q... If I`m going for a twin PSU setup, and one PSU is only gonna power the Mobo/CPU/ memory and maybe the opticals, which would be better: a single rail PSU with 34A or a split rail PSU with 34A total between the +12V rails?
Thanks very much,
Kenny
Squid_Spit
08-12-2005, 02:39 AM
On a dual rail psu one, rail is responsible for the cpu and the other for the peripherals.
Hey! Thanks for gettin back to me That seems pretty easy to follow :) From looking at the specs on a company webiste, is +12V1 for the mobo/CPU or is it the larger current rating that goes to the mobo?
RootX
08-12-2005, 03:32 AM
Well, according to the atx12v power supply design guide (http://www.formfactors.org/developer%5Cspecs%5CSFX12V_PSDGr3_%201%20public_br .pdf) (pdf, right click and save as if on slow connection) it states that +12V2 is the 4-pin connector while +12V1 is the rail found at the 24pin and molex connectors.
Figure 10 is kinda confusing though.
Hmmm. Does the 2x2 socket provide most of the power for the mobo? If not, that leaves the other +12V rail to provide power for the mobo and all the molex...a big draw. Good find though :) Big, but good
toledo
08-12-2005, 04:40 AM
Well , i was wondering .....Witch one is better : single or dual ? (assuming both 24 pin ) .
I have an Enermax witch has 36A on the 12v rail ,so what is the benefit of choosing one PSU that has 2 x 12v@18each ? :confused:
Depends on what you plan to hang on the end of it :)
Squid_Spit
08-12-2005, 05:29 AM
Well , i was wondering .....Witch one is better : single or dual ? (assuming both 24 pin ) .
I have an Enermax witch has 36A on the 12v rail ,so what is the benefit of choosing one PSU that has 2 x 12v@18each ? :confused:
Nothing really, we dont notice any difference
KoolDrew
08-12-2005, 03:17 PM
Well , i was wondering .....Witch one is better : single or dual ? (assuming both 24 pin ) .
It depends. Having a dual rail PSU will supply cleaner power of course, however the problem with a lot of dual rail PSU's is when running highly overclocked CPU's. With Prescotts reaching ~5GHz along with highly overclocked dual core or dual CPU machines many dual-rail CPUs may fail to work. The OCZ Powerstream 600w is a perfect example. I have seen people having problems with it and switching to the sinlgle rail 520w fixed the problem.
So if you are doing some very extreme overclocking a nice PSU with a beefy single +12v rail is best. The three top are the OCZ Powerstream 520w, Sparkle FSP550-60PLG and the PC P&C 510.
toledo
08-20-2005, 11:35 AM
It depends. Having a dual rail PSU will supply cleaner power of course, however the problem with a lot of dual rail PSU's is when running highly overclocked CPU's. With Prescotts reaching ~5GHz along with highly overclocked dual core or dual CPU machines many dual-rail CPUs may fail to work. The OCZ Powerstream 600w is a perfect example. I have seen people having problems with it and switching to the sinlgle rail 520w fixed the problem.
So if you are doing some very extreme overclocking a nice PSU with a beefy single +12v rail is best. The three top are the OCZ Powerstream 520w, Sparkle FSP550-60PLG and the PC P&C 510.
From what i`ve seen it is better to stay on the single rail land , as long as the psu has enough amps on the 12v rail . ;)
dual rail is good imo, one rail you can use for mobo\cpu etc while the other can deal with the "spiking" devices such as fans.
KoolDrew
08-22-2005, 10:31 AM
Dual-rail is good, but for some "extreme" overclockers a beefier single rail is best.
Like I say...depends on the load :) 12V compressors demand a single rail, for example :)
Malmedahl
06-16-2006, 11:02 PM
This thread is rather old but i found it touches what trouble i might have ran into.
I have an OCZ powerstream 600 for 1 year and 5 months. Its the verision with 1 PCI-E only.
It was first powering a FX55 with two 6800 Ultras but now running an FX57 with two 7800GTX
I have found there is something fishy about it now tho.
Completely shuts down the system under some heavy graphics intensive games such as FEAR with maximum details and certain scenes. Quake 4 with ie 16xFSAA & Doom3 with 16xFSAA.
A pal from Techsweden.org came along with his Epsilon 700w. I didnt check the specifications in detail but my system now ran completely fine where it else failed with the OCZ 600.
I also noticed his PS were giving about 12.25 under load. I found that to be rather high IMO. Tho i saw little to no drop in the voltage under load
Compared to mine wich were at about 12.10 idle and dropping to 12.04-12.05 under load. Then the system completely shuts down.
I have always been very restrictive as to adjusting the rails but since i so clearly saw it running fine with 12.25 i put mine back in and adjusted it to 12.20
I ran FEAR and tried this effect intensive scene wich the system ALWAYS had been shutting down on.
It ran just fine through this scene after the +12 rail had been adjusted from 12.10-12.20.
There were still some drop in the voltage and the system shut down later.
It was more capable after adjusting but not flawless.
It seemed i won even more stability by using different Molex connectors from the PS to power the PCI-E lane on the motherboard and different ones to the adapter wich are using TWO molex connectors to give one 6 PIN PCI-E to the other 7800GTX
The total wattage output from my whole system is 400-410W. Measured with a powermeter you put in the jack of the wall. This is under full load and including a vapochill and 220v waterpump.
The parts my OCZ 600w pwr supply powers viewed below:
DFI NF4 SLI-DR
FX57 3400MHz 1.57vCORE
2x512Mb Twinmos Speed Premium 262MHz 3.5vDIMM
2x XFX 7800GTX 256Mb (490/1300)
4x Western Digital Raptor 10.000RPM 36GB SATA
1xMaxtor 7200RPM 300GB SATA
1xWestern Digital Caviar 7200RPM 200GB SATA
1xNEC DVD CD/RW 3500A IDE
Onboard ethernet
Soundblaster XI-FI
Fancontroller
Vapochill Control Panel (USB + Molex12v)
Fans
4x120mm
2x80mm
2x40mm
Razor USB
Logitech K-Board USB
Should i raise the +12 even further or have i put alot of the load into same 12 rail? Seems there is nothing you can do to alter wich rail your parts (HDD, GPU) etc are using.
I must also mention that this only happens when im using highly performing Forceware drivers wich doubled the performance in games such as FEAR & Far Cry under maximum settings.
EDIT: Perhaps i should make a new thread about this considering this thread is rather old. Moderator?
ScottFern
06-26-2006, 11:50 AM
I also have a question. I have an Antec NeoPower 480W Dual rail PSU. It has a 12V1+ 18A and a 12V2+ 15A and I am not sure if its enough amps to power a 7900GTX, 3 HDs, watercooling pump, the CPU and Mobo?
Praxis1452
06-26-2006, 12:35 PM
It really depends on your situation. Dual rail's advantages are minimal. The cleaner power isn't really noticed widely. Also dual rails aren't for "spiking" hardware. Intel really just instated it because they thought if part of the power supply failed since a single rail failed with 20 amps rather than a single rail with 40 amps it will cause less damage. It's pretty rare that there are problems with dual 12v rails... But it's there especially if you aren't crossloading. For example You have a Crossfire Setup. 20-22 amps on 1 12v rail rated for 20 amps may not be enough even though the cpu rail has overhead. That's why 700W power supplies use 4 12v rails with 15 amps each ex. Fortron Epsilon. Though the rails can't be added.
DTU_XaVier
06-27-2006, 08:22 AM
On my (pretty modest) NorthQ 500W 2x12v-rail PSU, it's rail no.1 for CPU/mobo/everything gaining power through the mobo (fans plugged there, PCI-e slot, usb etc.), and rail no.2 takes care of everything else (molex/PCI-e pwr-connector)... There are some PSU-manufacturers who use more rails, fx. 1 specefied for each PCI-e lane, though these may be lacking in terms of power to the mobo/CPU, as each lane can't push as much power around... A single-rail PSU is better at supplying power where it's needed, instead of letting it go to waste :)
Best Regards :toast:
BlackThyra
02-16-2007, 11:46 AM
my DS3 mobo only have single +12v slot and i have Enermax Liberty 400W which has dual +12v rails (20A each) how use the other +12v rail?
is there a splitter for +12v rail?
No, you're fine. The DS3 has both the P4_Power for the cpu on the upper left corner, and the 24 pin. And the molexes for your drives, sata.. you'll be fine.
ziddey
02-24-2007, 10:45 PM
Damn, old thread but still good. But I have a question as well. I was always taught not to mix rails. Like, for instance not to drive a motherboard's 24pin with a different psu than say a pcie connect, since the differing voltages may cause each psu to compensate for the other and end in bad things. So is it true that one rail is solely for the 2x2/4x2? I'm figuring since if atx is on one rail but pcie is on another, wouldn't they ultimately connect at the psu and cause both rails to come together? I guess it'd make sense if one of the rails was dedicated to the 2x2.
Cracker
02-24-2007, 10:55 PM
PCP&C only does single rail... this should tell you something. ;)
:toast:
jonnyGURU
02-25-2007, 05:18 AM
PCP&C only does single rail... this should tell you something. ;)
:toast:
Which they just started doing last year.
Tells me they found something else to hype up in their "power supply myths" garbage.
dogsx2
02-25-2007, 06:56 AM
It depends. Having a dual rail PSU will supply cleaner power of course, however the problem with a lot of dual rail PSU's is when running highly overclocked CPU's. With Prescotts reaching ~5GHz along with highly overclocked dual core or dual CPU machines many dual-rail CPUs may fail to work. The OCZ Powerstream 600w is a perfect example. I have seen people having problems with it and switching to the sinlgle rail 520w fixed the problem.
So if you are doing some very extreme overclocking a nice PSU with a beefy single +12v rail is best. The three top are the OCZ Powerstream 520w, Sparkle FSP550-60PLG and the PC P&C 510.
You forgot the top single +12v rail psu.
This (http://www.jonnyguru.com/review_details.php?id=45&page_num=4) is the best single rail. :D
Edit: didn't notice your post was so old, long before this psu came out, sorry. This is an old thread. LOL
Cracker
02-25-2007, 08:14 AM
Which they just started doing last year.
Tells me they found something else to hype up in their "power supply myths" garbage.PCP&C is widely considered the best P/S one can buy. I bought one because of their no-nonsense approach to rating their products and their outstanding customer service.
It will be nice when Nvidia and ATI pull their heads out and start producing videocards that don't need a freakin nuclear powerplant to run. Then power supplies can go back to being as boring as cables. :p:
Oklahoma Wolf
02-25-2007, 08:24 AM
PCP&C is widely considered the best P/S one can buy.
Usually by those who own them, who often haven't tried the true but less well known competition for their units like Etasis, Delta, Seventeam, and Zippy ;)
Praxis1452
02-25-2007, 08:29 AM
Usually by those who own them, who often haven't tried the true but less well known competition for their units like Etasis, Delta, Seventeam, and Zippy ;)
exactly
Cracker
02-25-2007, 01:19 PM
Usually by those who own them, who often haven't tried the true but less well known competition for their units like Etasis, Delta, Seventeam, and Zippy ;)I believed that before I owned one.
BTW, how does one go about RMA-ing an Etasis power supply? Certainly it must be as simple as it is with PCP&C or even Antec. ;)
Oklahoma Wolf
02-25-2007, 01:36 PM
I would imagine it's through Etasis directly. Website is www.etasis.com.tw.
I've seen dead PC P&C units too, most recently a 1kW SR... it happens to them all. A company with a perfect track record doesn't exist. Owning one of each and then having one die doesn't automatically make the one that lived a better unit in the bigger picture. If my Silverstone died tomorrow, it would still be a better unit than the 2.5 years old and counting FSP 530W upstairs ;)
dogsx2
02-25-2007, 01:39 PM
BTW, how does one go about RMA-ing an Etasis power supply? ;)
If you bought it from Newegg the first year is duck soup.:D
Nanobot
02-25-2007, 03:32 PM
I think single rail is better
Look at my sig ; the Zippy I have is so old I have forgotten when I purchased it.
It seen over 20 system rebuilds and still runs everything flawlessly. It's voltage rail are flat lined, no fluctuation to speak of,even now that is has reached it's upper power delivery.
The 680i chipset's extra power consumption are loading it a bit high tho, so time for an upgrade.