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Single Rail vs. Multi Rail *Explained*

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post #151 of 160 (permalink) Old 07-26-2014, 10:26 AM
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Quote:
Originally Posted by Synthaxx View Post

Really a good read and a very humouristic way of explaining it to dummies like me whistle.gif
But I still have some questions about multi vs single rail, and an application to my case, in which I would like your opinion.

I recently acquired 2 295x2s and I'm still in need of a PSU that can handle these beasts. The whole PC will need more than 1500watts, even more when I decide to overclock the GPUs. According to AMD, they recommend 28A per 8Pin, and each card has 2 8pins. More information about the requirements in this link:

I'm intrested in a PSU above 1600watts, and currently, I think I have 2 options.

Option 1
The EVGA supernova 1600 g2, single rail, 133Amps total.

Option 2
Lepa MaxPlatinum 1700w, can peak 1800watts, multirail, 141Amps(?) total
Officially, the lepa has 30A rails, but the 295x2 already uses 28A/8pin without an OC, isn't this too close?
So would I then need to use 4 different 12v rails for each 8pin?
I read somewhere that OCP triggers at 40-55A.

What would be best in my case? My case does not support dual PSUs, so that would require to much modifications...


Congratz on your new monster cards.

Just to clarify, an 8-pin PCIE connector is not a Rail. A Rail is the OCP trigger point on the 12V line and other minor Lines.

A single 295x2 requires around 500w from the wall under full load at stock speeds (source).

Add another stock 295x2 and they should pull around 1Kw from the wall under full load.

Depending on your setup, it would be rare to see 4 GPUs under 100% load for long durations in the real world (games/drivers are not coded well enough) unless you mainly bench/mine/fold...etc.

The G2 should be more than enough for your needs and it is an excellent PSU with one of the best OEMs/Outstanding warranty.

RAIL Does Not Mean POWER.

Look up this Database before buying a PSU.

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post #152 of 160 (permalink) Old 07-26-2014, 11:25 AM
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Quote:
Originally Posted by eXXon View Post

Congratz on your new monster cards.

Just to clarify, an 8-pin PCIE connector is not a Rail. A Rail is the OCP trigger point on the 12V line and other minor Lines.

A single 295x2 requires around 500w from the wall under full load at stock speeds (source).

Add another stock 295x2 and they should pull around 1Kw from the wall under full load.

Depending on your setup, it would be rare to see 4 GPUs under 100% load for long durations in the real world (games/drivers are not coded well enough) unless you mainly bench/mine/fold...etc.

The G2 should be more than enough for your needs and it is an excellent PSU with one of the best OEMs/Outstanding warranty.

Thanks for your comment.
It's great to hear that the EVGA 1600 would suffice. I know that an ax1500i failed when both cards had a mild OC (1100/1400), while playing games, but maybe there were other factors involved (bad unit, many hdd/sdd,...).

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post #153 of 160 (permalink) Old 08-21-2014, 02:26 PM
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When i overvolt and oc my 290x's to 1.35 or more - the draw for each card is 480+ watts? Is that right?

I'm crypto mining right now at 1000/1500and i overvolted to 1.35 for this experiment, the power draw at the wall accordign to my killawatt is 1210 watts with bth gpus on and no load on the cpu

I disable one of the gpus and the load avg drops to about 730

Taking 730 from 1210 gives a final figure of 480 watts that isnt being drawn anymore by the card i just turned off

How is this possible?

The psu is a thermaltake 1350, which is a CWT puc unit with the dual psus on one pcb deal you mentioned in the OP

Is this even safe?!

Both cards are powercolor axr9290x-4gd5 oc reference models under water with EK full cover blocks (@60*c load if this makes any difference), with stock clocks that came at 1030/1250 flashed with the pt1 modified asus bios and overvolted/overclocked by sapphire trixx
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post #154 of 160 (permalink) Old 08-21-2014, 04:37 PM
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Quote:
Originally Posted by zvonkorp View Post

When i overvolt and oc my 290x's to 1.35 or more - the draw for each card is 480+ watts? Is that right?

I'm crypto mining right now at 1000/1500and i overvolted to 1.35 for this experiment, the power draw at the wall accordign to my killawatt is 1210 watts with bth gpus on and no load on the cpu

I disable one of the gpus and the load avg drops to about 730

Taking 730 from 1210 gives a final figure of 480 watts that isnt being drawn anymore by the card i just turned off

How is this possible?

The psu is a thermaltake 1350, which is a CWT puc unit with the dual psus on one pcb deal you mentioned in the OP

Is this even safe?!

Both cards are powercolor axr9290x-4gd5 oc reference models under water with EK full cover blocks (@60*c load if this makes any difference), with stock clocks that came at 1030/1250 flashed with the pt1 modified asus bios and overvolted/overclocked by sapphire trixx

The 290X definitely won't be drawing 480W on it's own, especially at stock clocks.

 

A 1000MHz/1.35V 290X will draw around 351W +/-5%. Even if you overclocked it to 1200MHz and upped the voltage to 1.4V it would still draw less than that, at around 453W.

 

Are you taking efficiency into account? At that sort of power draw your PSU will be roughly 86-87% efficient.



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post #155 of 160 (permalink) Old 08-22-2014, 10:51 AM
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Quote:
Originally Posted by twerk View Post

The 290X definitely won't be drawing 480W on it's own, especially at stock clocks.

A 1000MHz/1.35V 290X will draw around 351W +/-5%. Even if you overclocked it to 1200MHz and upped the voltage to 1.4V it would still draw less than that, at around 453W.

Are you taking efficiency into account? At that sort of power draw your PSU will be roughly 86-87% efficient.
Thats what i forgot. Efficiency LOL thank you so much for remind ingme!
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post #156 of 160 (permalink) Old 03-31-2015, 11:16 AM
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Good reading. Thank you OP! thumb.gif


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post #157 of 160 (permalink) Old 08-09-2016, 03:47 AM
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F**k! I really thought I'd find the answer in this text, but I didn't.

I have a multi-rail PSU 22+22+25+25A which previously ran a GTX970 with 8+6PIN ATX-power which would mean 22+22=44A maximum at least right?
Now I have installed a GTX 1070 with a single 8PIN AT-power and rumors say 1070 need 30A.

This might be a problem (If it's not my motherboard that is broken) right?

Having the card installed I lose 4/6 SATA-connectors and everything connected to those frown.gif
Running benchmarks Time Spy lags incredibly and reports a result of 1.200p when it should be around 5.500p
FurMark works without pproblems though. So do Unigine benchmarks and gaming Dying Light for example

I don't get it!

I've even tried to pull the power to the GPU with two molex connectors and a Y-splitter to pull the power from two different rails. That didn't help other than I got my SATA-ports working again. The benchmarks still reports the same frown.gif

I wonder if a Single rail PSU with +12V 50-60A would be a better choice!?
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post #158 of 160 (permalink) Old 11-26-2016, 01:50 AM
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Like @eXXon stated above, another 8+6pin pci or molex connector/cable isn't another rail.

I have a similar problem as you. I have the beQuiet Straight Power 10 600W CM and it has 4 rails 18/18/20/20.
After using many psu calculators and calculating the Wattage needed for my system, I came to the conclusion 600 Watt would be enough even if I do a good but not too aggressive overclock. (CPU i5-6600k @4.5GHz with 1.3V and MSI R9 390 @1150Mhz with mv+25). tests worked fine, but were a bit unstable.

now my R9 390 pulls about 19 Ampere when I don't overclock it and run heaven unigine (see gpu-z)

Once I put in +50mv to get a higher overclock the Ampere drawn, according to GPU-Z, is 23.2 (I even reached 25 in some cases).

So 23 Ampere is of course way higher than 18 or 20 Ampere allowed per rail.
So i came to the conclusion that my PSU shuts down or puls back (or whatever) due to the relation Ampere needed to Ampere provided per rail. So I also used 2 different PCi connectors/cables from the PSU instead one 8+6, I used one 8, and another cable with 6 pins. that made it slightly more stable but still experienced dropouts.

Anyway, I am guessing (correct me if I am wrong) rails means it splitts the overall allowed Ampere to be more safe. Problem is, if you have one component that draws more Ampere than one of the rails, the comp might shut down due to safety reasons. And it does not mean, connecting more cables to that one component allows you to deliver more Ampere than per rail.

So in our case, we would need a psu with multi-rail Ampere of min 30 per rail (and then you find yourself in 850W PSU like the Dark Power) or single rail PSUs.
But I need a minimum of 650 Watt and 30 Ampere which leaves me with fairly expensive multi-rail PSUs or I go single rail with 50+ Ampere but that gets to unsafe for me, as I like to cut PSU cables to fit perfectly in my fairly small case Anidess A7.

The choices we have to make rolleyes.gif

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post #159 of 160 (permalink) Old 05-10-2017, 03:03 AM
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okie dokie could you tell me about whats good when it comes to designs that produce the rail in the first place say , buck converters or clamp circuit designs basically the dc to dc thingy
. see i have been through around 5 psu's in the last 5 years all differant sizes and sorts sometimes because i had pluged in video cards all on one cord which i have assumed is called a rail i am learning trying to at the moment i,l get it right this time .
what makes it hard is that the technology doesnt change it,s nappie quite as fast as intel and amd through my mobo and and cpu in the bin, and i still find myself looking up the same amazing psu that has awsome features that i did back when i was spooning over core proccesors and hdmi .
wiki pedia didnt help me much anymore then the guy at the computer store did infact they both think they know everything its just the guy at the computer store assures me that the x psu is capable of providing and wikipedia assures me that they are lying and using false advertising ect quote " many manufacturers have chosen to ignore the requirement and increase the current limits above 20 A per rail, or provide "single-rail" power supplies that omit the current limit circuitry. (In some cases, in violation of their own advertising claims to include it.[8]) The requirement was deleted from version 2.3 (March 2007) of the ATX12V power supply specifications.[9]
Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry,[10] both for cost reasons and because it is an irritation to customers.[11] (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)
i like nuc devices but i am trying to build a pc so any help about the electronics would be helpful ,
i think my biggest problem is i am trying to use a 95 watt high powered cpu on a device that only has around 120 watt being the 5 vlt and 3 vlt combined but only have 20 amps due to restriction associated with the 20 amp rule. (I wanna know about the device cause I don't always see the relevance mathematically between the amps and watts.) so it needs to be jerry rigged , so what ! also The board only uses 550 watts but i need around a 1000 watt to get it started and even then the whole machine runs at 0.5 amps which is just defeating the whole kinda idea in the first place. ( maybe jerry rig the 3 and 5 rails to be stronger or better and get rid of the excess watts outa the 12 volt main rail cause I was never really using them, then I just have to find a way to let it idle with out burning on the wires for no reason.) any way this time i hope i get a decent psu cause the guy down at the electronic repair man got to keep the last 4 or 5 cause he knows how to fix it probably but its kinda a hassle and cause the stickers have been removed its too hard to buy those parts ect ect.
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post #160 of 160 (permalink) Old 03-26-2018, 12:41 PM
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Thanks a lot. That explains it.
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