Single rail 1500w PSU suggestions

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clayton006

[H]ard|Gawd
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Jan 4, 2005
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So I've noticed my SilverStone 1500w power supply isn't cutting it for my over clocked Titans. I'm drawling too much off of their weirdly set up 12v rails. If this was a single rail PSU then I wouldn't be having issues.

So I'm looking at purchasing two power supplies. An option would be the 1200w corsair unit, the EVGA 1500w unit, or a different unit altogether. Any suggestions?

(And yes, I have two dedicated 20A circuts in my home that can handle this load with ease)
 
I believe I'm close to pulling over 500w a card so two single rails PSU's may be needed especially if I install my 4th Titan...
 
We're talking about an ST1500 here I assume. Is your symptom that your system is turning off?
 
The OCP isn't kicking in, but it's freezing up at a certain point which I found out was related to over drawling on it.

If I put in my hx1050w for one GPU, and mix rails on my ST1500 for my other two Titans, splitting the load allows me to run the O/C with no issues.
 
Gotcha, and because of how the PCI-E connectors and rails are split, you can't do separate 12V rails for each PCI-E connector, and certainly not for four cards worth.

The EVGA 1500W is junk. You have a 900D, so maybe running dual power supply is the right choice if you're going four card. You're probably tipping over 1kw at load as-is with three OC'd titans. The only other single supplies that come to mind are the Enermax MaxRevo and the Lepa G.
 
Yeah that's right where I was last night.

I'll take a look at the Lepa G, the Lepa I was looking at last night didn't seem single rail but I may not have been looking at the right ones. I've heard mixed reviews on the EVGA ones, but I like EVGA's customer service and I'm in touch with a lot of those guys on a regular basis so if I had any problems they would be quick to step in.

Thanks again for the advice / heads-up.
 
Yeah, but I also just realized that a single rail unit at this power level is probably a bit more risky than I should probably be going, but mixing the rails on this unit could prove to work in the way I need it two (not mixing between power supplies obviously).
 
The Lepa G1600 looks promising, just hope 60A per video card (30A to 6pin and 30A to 8pin) will be enough.
 
I'm close to 580w a card right now. So if 8pin carries the majority of the load then I'm still probably screwed unless at the point in just consuming too many wats total for my 1 PSU to hand as it is.
 
I do not at all see how you are 580w per card, testing wise they are ~375w a piece at stock, I am quite sure 1x6 and 1x8 would not be able to supply 580w. I have had freezing on my cards this could very well be related to overclocking them to hard. Titan does have built in voltage monitoring and if it does overdraw(not sure the max they are allowed to draw) or clocks are to high for the core or memory to support it can artifact, freeze, or crash.

some power supplies split the 12v lines quite well so the cpu and board gets some of the power and the rest gets shifted between pci-e 1 and pci-e 2 so that one can load it properly.

Either way, I am not sure limits on 12v that power supplies can shoot out, but asking for 1500w on mostly 12v seems like they would have to do multi-rail type, say HX1050 power supply, it is 2 550w dedicated power supplies so that each rail gets ample power, better in my mind to go this route then to have 1 monster rail that might end up getting far hotter then 2 dedicated but smaller amp rails, possibly less loss in conversion as well?

pci-e is 75w, pci-e 6 pin is 75w, pci-e 8 pin is 150w so that's 300w, they can go over this a bit I believe pci-e can do ~90w 6 pin around 100 8 pin 175 but if you claim the card is drawing 580w and you have voltmetered it so you know this without a doubt, then no wonder it freezes, it is way beyond spec, 420w would be pushing it per card least so far as I have seen. Not sure if putting it in a pci-e 3.0 slot gives it more available power per slot.

funny though some good points. http://www.antec.com/PSU/index.php
 
You are correct, I overestimated by a good bit. This is some testing copied from a member of the overclock.net forum who did some calculations. Much lower than 580w but still over my 25A limit....

His numbers for going over limits were based on the specs of my SilverStone ST1500

From OccamRazor @ overclock.net:
While you might have up to 100A of power in all 4 rails, divided for your 3 cards its not enough when you go up from 1,300V,(if you had 50A avaliable per card you would have 150A for the cards and at least 30 to 50A for the rest of the system meaning a +2000W PSU); the rest of the 12V rails, two are dedicated to the EPS12V/ATX12V cables alone. That's 50A for the CPU!
Still you have to mix rails and dont up the voltage too much or you will have shutdowns when the amperage is not enough and trip the PSU´s OCP (shutdowns)!
Bottom line the max rail limit is limited by the max psu output! If you add all the rails amperage you see its over the maximum amperage the PSU can supply; 110A!

1,3V@125% TDP <=> aW x b% = cW (a= bios base TDP, b= OSD TDP, c= aproximate power draw)

<=> 300W x 125%TDP = 375W

I(A) = P(W) / V(V)

<=> 375W / 12V = 31.25A
As you can see over the 25A rail limit!

Now, some tests i made:

Bear in mind that my system is in my SIG and the only difference was the [email protected]@1,30v! Using triple monitor 3240 x 1920@120hz SLI TITANS W/ Skyn3t Rev2 bios
and memory at stock 6000mhz!

1306mhz / 1,37v / power draw 124% / load 99% 372W*
1333mhz / 1.37v / power draw 134% / load 99% 402W*
1359mhz / 1.37v / power draw 139% / load 99% 417W*
1385mhz / 1.37v / power draw 145% / load 99% 435W*
1400mhz / 1.39v / power draw 155% / load 99% 465W*
* Power draw for 1 card alone
 
wow, that is just confusing the way he explains that, not once have I ever heard 300 x125% TDP that does not at all make sense to my understanding not have I ever seen this in any reading I have ever done.

the rails have OCP on them (they are supposed to with any decent power supply) multi-rail is fed by a "master" if you will, the combined 12v is one number to look at, then you take the 12v 1 12v2 etc to see what they can give out, most makers are smart enough to dedicate x power to pci-e for graphics use, going by what he is saying up there, 50ax12v gives 600w to the CPU alone? LOL what.

It depends on the pin outs and such, yes cards can go over their rated TDP and Titan are near the top power draw for any card out there, but still, I do not at all picture just 1 titan drawing 465w (38.75amps) if it used dual 8 pin pci-e power connectors(6+2 is still 8 pin) that would give a total of 375 directly available with ~435 or so max draw without being over spec.

Either way your PSU is 8 rails 25a per, 110a total with 1320w combined total, if each gpu draws what he states 465w that's 930w leaving 340w on the 12v for everything else so, no you cannot add another titan.

guru states for their review
Each of 12V5 to 12V8 is dedicated to one chain of PCI-E connectors. Each of those rails gets one 6+2 pin and one 6 pin connector. Enough for four cards. And with a 25A limit on each rail, it is very unlikely you'll run into the overcurrent protection, even with the most powerful cards now on the market. And if you do, with four 12V rails dedicated to only PCI-E connectors, you can always start combining, as this unit draws its 12V water from one big pool.

Of the rest of the 12V rails, two are dedicated to the EPS12V/ATX12V cables alone. That's 50A for the CPU... just try and use that up, I dare you. The remaining two are for the ATX and peripheral connectors, with one of the four peripheral connectors on 12V3 and the remaining three on 12V4. You're probably not going to use up that combined 50A either.

Anyways, maybe don't overclock the cards like you are then and you should be fine for 3 titans, as they are ~350-375w stock gaming loaded so 375x3=1125w or 94a of 110a available leaving 195w for cpu etc, I know from experience declocking a touch does not hurt performance very much and can save a ton of power especially memory declocking (I can run BF4 with my 7870 just fine massively declocked still running medium-high settings at 1080p)

Anyways best of luck. TLDR this is possible and yes you can "mix rails" if each rail is dedicated to the connectors being used, then it can take x from the one connector and x from the other so in this case there is a total of 4 rails each having 2 connectors for gpu use, if you are only using 3 cards you are using 6 connectors of 8 available which means one card would be using 1 rail by itself the other 2 cards can "mix" the remaining rails. 50a per card is way more then they can use (LN2 maybe :p)
 
clayton006 said:
The OCP isn't kicking in, but it's freezing up at a certain point
Click to expand...

If the PSU's not totally shutting down, your issue has nothing whatsoever to do with the multi-rail overcurrent protection. Neither are you overdrawing it. There's something else at play that adding a second PSU cures.

That said the ST1500 was good in its day, but that day is pretty much over. Units like the Lepa G-1600 are a bit more optimized for modern watt monster rigs.
 
agreed on this point above. For me if I was clocking to high, it would freeze more often then not, not enough core voltage or to fast, artifacts, memory to fast, performance spikes/dips temporary freezing for driver to reset and/or full lockups, sometimes this takes a few minutes, other times it could be hours, but generally if it was related to power, considering what those cards can suck back I would think if the PSU was directly at fault, it would not just freeze out of the blue, it would crash. I would think about reducing the clocks somewhat to see if this helps.

As Oklahoma pointed out, if there is OCP on the rails, they wouldn't just freeze a bit but still let power through to do its thing, OCP is designed to KILL the power to prevent failure of the rail or power supply in question so catastrophic failure does not occur, very much like a circuit breaker, hold it at 99% and its fine(though not recommended) hit 100%(or a surge) even for a moment and it pops, eventually it will fail and not be able to be used, anyways, point is, it either works or does not, it would not kind of work, generally an overdrawn PSU gets very hot and it might run for a bit but once it freezes full lock it is very rare it does not cook itself in the process, they do have the safeties in there for a reason.

2 separate power supplies is not a bad idea though, 1 can run cpu and 1 gpu, the other can run the others. Just reading some of what you wrote initially, they are not badly set up rails, they are well designed for what they unit can do, the rails meant for GPU usage are dedicated to them 1 connector from each rail gives more then ample power for SLI/CF cards well maybe dual highly overclocked 690/590/7990 might be different :p
 
Oklahoma Wolf said:
If the PSU's not totally shutting down, your issue has nothing whatsoever to do with the multi-rail overcurrent protection. Neither are you overdrawing it. There's something else at play that adding a second PSU cures.

That said the ST1500 was good in its day, but that day is pretty much over. Units like the Lepa G-1600 are a bit more optimized for modern watt monster rigs.
Click to expand...

This.

As stated in the article I wrote that was linked above... if the fact that the PSU was multiple +12V rail versus single +12V rail, the PSU would be shutting down.

Freezing, artifacts, etc. have ABSOLUTELY NOTHING to do with "how many" +12V rails you have.
 
Thanks Johnny I appreciate it. Sounds like if it ain't broke don't fix it mantra here. I'm probably just at the limits of what my cards can do.
 
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