• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Multi-rail PS w/a mono-rail sys?

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

D17S

Registered
Joined
Dec 1, 2005
Need a little advise. I bought an AGP 6600GT just to get me by for a while longer. My current 2.8 O/C’d very nicely from 3.1 to ~3.4 with that new thermalright XP-120 heat pipe. Those things are magic. But my system is still just not “Uber” enough to be able to really take advantage of a 6800 and I really don’t want to throw any more $$s at AGP. But I’ve run into a problem . . .

Question 1:
The graphics are fraggin’ badly. All the weird symptoms of an overloaded PS. My Enermax EG365P may have hit its limit with that 6600GT, but my voltages all stay perfect. I log them with MBM during a frag’ing session with MSFS or LOMAC, but the symptom is still very suspicious! I guess question # 1 would be “If voltages remain within limits, is this a positive indication that the PS is still fully capable of providing full current to the load.” Or the same question asked the opposite way: “Will a voltage fall-off always occur as the ‘observable’ electrical indication that a PS is being overloaded?” As far as I know, there is no way to directly measure amps without add-on equipment: So, if dropping voltage is not a way to see this, is there some other way to confirm that a power supply is NOT providing all the current the load is asking for?”

Following up with a possible explanation for a lack of falling voltage level: “Is a PS designed to throttle back amperage to so that it can maintain a rated voltage level or perform the function of a softly landed circuit breaker?” But then to continue the discussion: “Wouldn’t the PS ‘spend’ at least some voltage to maintain amps for at least a little bit?” I’m really looking for a voltage drop as an indirect indication that amperage is NOT being maintained, but not seeing it. My little ‘ol power supply’s volts are staying solid as a rock

Question 2:
So what do you think? Well how about this. Setting my bad case of technoiditis aside for a moment, I can see the writing on the wall. In a year or so, I want that FX-6X, SLI’s 7800 rig and it’s not going to hurt me to get this system’s PS now. But in the mean time, I will be using it with a system that is more suited to a mono-rail system and . . . .

This dual/ triple/ quad rail thing has me baffled. What are they doing here? Well, I have an idea, but how can I appropriately use it with my current system. Are the various 12v busses simply hard wired to various plugs? For instance, in a dual 12v buss PS, is one of the 12v busses hardwired to the main and drive connectors and the other to the “SLI Qualified” PCI-E connectors? . . . or are there sensing circuits in the PS that switch the load on the basis of a connector it sees plugged in. (My concern is that this might be a little too much wishful thinking.) Will I need to get a PCI-E to Molex adapter to even utilize that second/third / even forth buss (Jeeze, it’s getting to be like the # of blades in the latest razor!) . . . if I don’t have a whole box full of PCI-E Vcards?

T’was recommended here by a real knowledgeable guy. Thought ya’ll might have some fun with this . . . .Thanks in advance.
 

Know Nuttin

Senior Member
Joined
Mar 25, 2004
Location
Ontario, Canada
For the split rail PSU's, they are hardwired internally. For example, 12v2 is for CPU. 12v1 powers everything else. In a quad setup, 12v1 would normally power CPU 1 and 12v2 for CPU 2. I haven't seen the full spec sheet for a quad setup, and all the quad rail setup info that I've seen so far from manufacturer's, seem to vary slightly on what powers what (12v3 and 12v4).

My understanding is that for a split plane (quad rail) setup, 12v3 should be powering the motherboard and the components plugged into them. 12v4 should be powering any devices connected by molex/SATA/PCI-E power. In other words, devices that are plugged directly into power coming from the PSU itself.

For a common plane, 12v1 = CPU, 12v2 = motherboard, 12v3 = everything else plugged directly into the PSU, like 12v4 is for a split plane.

Using MBM to monitor voltages is not the best way. A digital multimeter is still recommended. An overloaded PSU will normally just cause a reboot but you could experience other issues if it is not being overloaded heavily. Slight graphics anomalies, which is probably what you are experiencing.

Is it possible for you to try to run the Enermax outside of the case? Enermax's sometimes have problems maintaining steady and rated power when placed inside a case.
 
Last edited:
OP
D

D17S

Registered
Joined
Dec 1, 2005
Good info, thanks or the reply.

Well, I spoke to both Antec and Enermax. Antec said their 3 rail system was just false advertising. It's actually a 2 rail system. For instance the 3 ,18 amp rails on the HE550 are actually one 18 amp circuit that powers the CPU and one 26 amp circuit that powers everything else (including the MoBo). He said it's not a 3 rail system. It's a 2 rail system. I asked "Then what's the deal? The tech said "I'd like to know too, but it became apparent that I had better quit asking."

I looked the Antec over. Only the 20/24 pin main and the 4 pin CPU plug were hard wired into the PS. There were 5 socket connectors on the PS that were available for various peripheral leads. There were no marking on the sockets that this socket was for this 12v buss and an other socket was for a different 12v buss. There were unmarked. You just plugged in whatever you needed. Couple of HD and a couple of PCI-Es. . .whatever. Physically, it looked just like exactly what the tech had described . . . A single 12v buss for ALL the peripherals.

Enermax said they didn't have a 3 rail system, but their 2 rail systems work the same way. One 12v rail for the CPU (and the MoBo, like you described) and one for everything else. The only thing different about these multi-rail power supplies appears to be independent power to the CPU/(MoBo too).

This is a very good thing. But it is not what a "SLI qualified" 3 rail system for use with an SLI'd set of PCI-E cards suggests to me. It misleads. It appears to be a 2 rail system that has nothing to to with a PCI-E video subsystem. Antec describes that splitting off the second 12v rail was to necessary to deal with the increased load of the new dual core CPUs.

I am really just trying to unravel this marketing hype. Antec and Enermax described their power supplies as 'simple' dual 12v rail systems. The CPU gets one rail and any PCI-E card (or SLI'd set) will share a rail with the HDs, opticals, floppies and all other peripherals. So, does "SLI qualified" just mean, "Lots of amps on the peripheral’s 12v rail'? So it seems.

As long as we know what’s going on we can deal with this. For instance, with a 3 rail system, I might have thought my PCI-Es were independent . . . so 6 or 8 drives, a half a dozen USB gizmos and everything else will not affect my video performance. But if what I’m hearing form Antec and Enermax is true, my video is still as vulnerable to an overloaded system as it ever was. I just will now have more amps to work with.

What cha think? Is this your experience too?
 
Last edited:

Know Nuttin

Senior Member
Joined
Mar 25, 2004
Location
Ontario, Canada
SLI qualified simply means that it has been tested and certified to sufficiently power SLI setup, and with dual PCI-E power connectors. Now, that doesn't take into account what you may have in the system. I don't know what they use to certify it with, in terms of testing equipment and what not. You don't need to have a dual rail setup to be SLI Certified. The OCZ Powerstream 520w and the Sparkle FSP550PLG-SLI are SLI certified yet are single rail +12v based.

12v2 (which is the 4pin square power connector going to the board) is for CPU only, iirc. It's not for motherboard power. Motherboard power comes from 12v1 and that is found on the ATX 24pin power connector.

The dual +12v was to meet recommendation for the 240VA limit. Anything above that on the +12v, should have a second +12v rail to avoid going over the 240VA limit.

It depends on whether you are buying a real 3 +12v output or, like in Antec's case.

Your best bets for SLI is to avoid going with only a dual +12v setup, and move to a single +12v rail. Best options here are the OCZ Powerstream 520w, Sparkle FSP550PLG-SLI, Zippy HP2-6460P/HP2-6500P, or PC Power and Cooling 510 SLI.
 
OP
D

D17S

Registered
Joined
Dec 1, 2005
Ahh, now it's starting to make sense. Anything above 240VA (or ~20 amps on a 12v buss?) needs at least the description as a its own buss. I'm seeing 22 amps on the 12v-ers here and there, but that is probably just a transit capability. Their numbers get a bit optimistic sometimes.

I heard a single 6800 can need up to 10 amps. Are the 7800s even hungier? That's potentially 20 amps right there for just the video subsystem in an SLI's rig. If you think about it, a single rail at a 240 VA limit really couldn't provide power for both cards. Somehow 2, 12v busses would have to be combined to get any kind of elbow room. It's making more sense now.

Without going totally esoteric, what's the PS to have these days for a fully loaded system (SLI'd 7800s, with 2 opticals, a floppy, 3-4 HDs and a couple of USB gizzies). Do you like the dual buss setups? And if one really exists, how would a 3 buss system work and would it be a rational choice.

And if I had to choose, I'd say the dual core processors are not for me, yet. And those FX-5Xs sound a bit overdone when that little 'ol 3000+ Venice will turn up to 2.6-8 . . . on air!
 

Know Nuttin

Senior Member
Joined
Mar 25, 2004
Location
Ontario, Canada
7800's draw about the same as the 6800 series. A few watts more. At peak, it's around 80w for the GTX, and 77 for the 6800 Ultra's.

I'm not a huge fan of dual bus setup's for power hungry systems at all.

USB draws from 5v. Optical's/HD's draw from 12v and 5v. floppy is negligble.

I would recommend what I did above. The OCZ 520w, sparkle 550, PC power and cooling SLI 510. Also add the Etasis EPAP-560.
 
OP
D

D17S

Registered
Joined
Dec 1, 2005
Thank for the list. Did a little shopping. That Etasis EPAP-560 looks hopeful. Any reviews pop up yet? (Even Google struggled a bit.)

The mfg's are still having fun with the 12v rail question. Antec was advertising that power supply with 3, 18 amp 12v rails. That's a whoppin' 54, 12v amps available. "Woah." I said. "Get me some of that!" But the mfg finally said it was actually a 2 rail system with the other 2, 12v, 8 amp rails combined. It's now been modified further. "So," I asked, "that's 2x18=36 amps for the #2 rail?" Nope. Still just 18. It's a jungle out there.

I'm becoming less enamored by this dual rail setup the more I learn. If they have taken an otherwise (potentially) strong 36amp, 12v system and split the capacity, that only leaves me with 18 amps for my Vcards and drives. There's no way I would trust an 18 amp, 12v buss to power a couple of 7800GTX and a raided-up gaggle of harddrives and opticals.

Also, do these new CPUs really need 18-20, 12v amps? If not, and these dual rail systems are in fact completely isolated 12 volt busses (no sharing), it sure seems the mono-rail PSs are still the way to go. Give the system 35+, 12v amps and let who ever needs it, have it.

Any thoughts?
 

Know Nuttin

Senior Member
Joined
Mar 25, 2004
Location
Ontario, Canada
No reviews that I am aware of but it's an industrial grade unit and it's made to last. Also, the power ratings are given at 50c.

An overclocked Pentium D or Prescott with extra voltage can push upwards of 150w +. You probably won't need 18A but you don't want to get too close to that number either.

I still like the single rail +12v (even though I have a dual rail unit). The Zippy 700w has 45A on the +12v. Now that's a beast.
 

Oklahoma Wolf

Senior Warranty Validity Sealed Stick Remover
Joined
Mar 18, 2003
D17S said:
Thank for the list. Did a little shopping. That Etasis EPAP-560 looks hopeful. Any reviews pop up yet? (Even Google struggled a bit.)

Look for the Etasis built Silverstone 560w instead - it is pretty much the same unit. This one will have some bling factor to it, whereas the OEM Etasis model may lack one or both PCI-E connectors. No good reviews yet, but they're coming I'm sure - SPCR has it listed in their upcoming reviews page.

The Zippy 700w is a real workhorse, but longer than normal. One 80mm fan, but very efficient. They have a 600w dual 12v unit that will handle SLI with a combined 40A @ 12v limit on dual 20A and 26A 12v rails, but I too tend not to recommend anything but single 12v designs for SLI or P4 overclocking. Sometimes I recommend a split plane quad 12v SSI unit if a lot of hard drives (6+) or more than one CPU are being run too.

And welcome to the forums!