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How To Calculate Graphics Card Needed?

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January 24, 2011 1:01:44 AM

I have seen an article about this before, but I can't remember where I saved it.

Basically, I want to know how to add up the wattage that my computer will use at max by looking at the devices connected to each of the rails (3.3 V, 5V, 12V). I want to do this instead of just using Antec's PSU calc because I want to make sure I have enough power for the devices connected to each rail. For example, I may have enough power overall, but a certain rail may be overloaded (this is how it works right?). I've heard a lot of discussion on one rail versus lots of 12V rails and it seems like there isn't concrete answer as to which is better. If you have multiple rails does all the power work fine anyway or is there a limit to the amperage on each rail?

I'm asking because I may be getting a new video card in a few months (something like the GTX 460) and I don't know if my Antec 550 TruePower Trio is going to be enough
a c 288 ) Power supply
a c 202 U Graphics card
January 24, 2011 1:10:08 AM

If you arent using adapters it will be near impossible to overload a rail, 80% of the system power is pulled from the 12V rail these days, AFAIK only memory, HDD and optical drives pull from the minor rails with any significance so you can ignore them.

For most things, find its rated wattage, a GTX 460 needs about 160W per card, the CPU wattage is stated too, most other things wont be too significant, about 6W per fan, and maybe a few watts due to the hard drives, if you have a mid range system your main concerns for the 12V rail are CPU and GPU, assume the rest of the system needs about 80W of power and you will be fine.

With multirail PSUs, it really depends on the internals. There are some that claim to have multiple rails but they are all joined up in the PSU so they act as one big one, there are others which are truely multirail which have OCP on each rail and will shut the unit down if you exceed the load on a rail.
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January 24, 2011 2:46:58 AM

Well, I'll have to check to see if the Antec I have is a true three rail or not.

Anyway, where are you getting these wattage minimums for graphics cards? Some of those seem pretty high.
The numbers PSU or GFX card manufacturers tell you is likely to be high to push sales. I know a Volt times an Amp is a watt, so I guess most of what I need to know is how to determine what rail is powering what, and where to get accurate load info on graphics cards (I'm guessing the tech sheet).

Of course, I'll still have to see if my CPU is good enough to bother with a new GFX card (I have a 8800GT 512MB right now). I've got a Core 2 Duo E6600 2.4GHz overclocked to 3.15GHz, but I don't know if that will be good enough to bother getting just a new GFX card for the likes of Deus Ex: Human Revolution, Crysis 2, Batman: Arkham City, Mass Effect 3. I also just bought Battlefield Bad Company 2 so I'd like for that to look good as well.

I'm still playing games in 1280x1024, and I'm not really sure what the CPU and GPU standards are for "average" graphical quality on a 1600x1200 or 1920x1200 monitor. I have a 1920x1080 42" TV but I hear that the quality on a screen that big wouldn't be nearly as good as a dedicated monitor.
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a b ) Power supply
a b U Graphics card
January 24, 2011 5:14:30 AM

A 550W Antec will be more than capable of handling a GTX460.
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a b U Graphics card
January 24, 2011 5:37:00 AM

Your C2D @ 3.15 would still work "good enough" with a new video card. Though probably past a 6850 or GTS 460 1GB, your gains would probably become smaller and smaller.

You could compare your screen resolution (the 1280x1024) to 1600x900 in reviews (or 1600x1050 for others). Most of the time you'd see that even a GTS 450 is even plenty fast. BUT, most new games are being made in the widescreen format. There would be a big benefit to playing in your 1920x1080 screen, it's the fact that the screen would be filled with picture rather than 2 black bars.

* I'm assuming that you play at 1280x1024 because you have a regular 4:3 screen.

The PSU rating by nvidia is over by 150W or more. They just like giving really high psu ratings just to be 100% sure that it works on your setup.
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a b ) Power supply
a b U Graphics card
January 24, 2011 2:29:57 PM

I've pretty much quit using PSU calculators (which tend to be on the high side to compensate for "POOR" quality PSUs), instread I google the video card and look at the reviews (Power consumption) and base my PSU requirements on these ( look at what GPU you are planning on using and for what you might upgrade too.
Then select a GOOD quallty PSU that is at least 20 % greater than the wattage specified for any anticipated upgrade to the GPU. Don't forget to look at test bed and make adjustments for CPU (ie did test bed use a midrange CPU and you have a OCed high end quad core which could added 5 Amps to 12 V rail)

http://www.bit-tech.net/hardware/graphics/2010/12/15/at...

http://www.hardwarecanucks.com/forum/hardware-canucks-r...

http://www.hardwarecanucks.com/forum/hardware-canucks-r...
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January 24, 2011 6:57:44 PM

Yes, I play on 1280x1024 because I have a monitor from late 2007. I'm not sure if the 42" TV I have would look good for PC stuff or whether it would look blurry because it is so big (a 1920x1080 monitor seems like it is normally 25"). Also, unless I have a beast of a GPU (with an HDMI port) I don't think my computer could handle a resolution of that size. If I have to upgrade my GPU, processor, PSU, and monitor its pretty likely I'd be sticking with what I have. If I just have to upgrade the GPU and PSU (either using the monitor I have now or using my TV) then that is a lot more reasonable.

I'll just have to do some more looking and see how good everything would be for a GPU only upgrade. I don't want to get a Geforce 460 and have it only stay decent for a year or so (this 8800 I have I got 3.5 years ago and it is still adequate for everything I've tried), and I don't want to get something better and have it be bottlenecked by my CPU. Things are going to be bad though if I "need" a new CPU because that means a whole new motherboard.. (I don't think I'll have to get new RAM, but if a motherboard is DDR3 only I'm out of luck.. I've only got 4GB of Corsair DDR2 800Mhz)

RetiredChief, I see what you're saying about looking at the typical load for GPUs, but if my power supply has three 12V rails and some of the rails are drawing more current than they are rated for that can't be good. So, how do I know what devices are on which rail so I can make sure the rails won't be possibly overloaded?

Using the Antec PSU calc it says at max load, with 30% capacitor aging, 90% and a 1GB Geforce 460 I would use 515 watts at 100% load. For the Geforce 580 it says 676. For the Radeon 6970 it says about the same. Radeon 5970: 644.

So, I know how much I'd generally need, I just don't know which devices are on each rail. Also, even if it isn't completely necessary, I'd like to know how to calculate the PSU load per rail manually just for general knowledge (I wish I could find the article with all this stuff in it..)

Also, What do you mean checking the test bed? What is that? Are you talking about figuring how much extra power my overclock is pulling from the 12V rail? According to Antec's calc, at 90% TDP it uses 85 watts. By the way, mine is a Core 2 Duo E6600, only a dual core.
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a b ) Power supply
a b U Graphics card
January 24, 2011 7:23:11 PM

Generally multi rail units have a rated power per rail and a max power per rail because what happens is the power supply will automatically combine the power and distribute it as it is need on a rail to rail bases. As somebody else has said I believe as long as you are not using an adapter on any of the strings you have nothing to worry about. The power supply will distribute the power where it is needed without problem. Since you said its an Antec too as long as its a sufficient amount of power for what you are using it for I would not worry about it.
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a b ) Power supply
a b U Graphics card
January 24, 2011 8:15:04 PM

For the normal individual and selecting a quallity PSU that is at least 20 % > than need you will have little to worry about.
For example Rail 1 will go to the MB (4/8 pin ATX power and 24 pin connector. Rail 2 wil go to the PCI-e connectors and say rail 3 to the HDD/DVD drives. MB manf and GPU makers will ensure that the Power drawn will be less than specs. The problem came from older psus and som ***&%&&*^ psus.

My igreen psu is an exception - +12 v rails can all draw their rated max value, BUT rail 1 is 18 Amps (MB), Rail 2 is 16 amps (to ATI 5770 GPU) and rail 3 is only 4 Amps (1 SSD, 2 HDDs, 1 Blu-ray writter and 1 DVD writer.
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a b ) Power supply
a b U Graphics card
January 24, 2011 8:30:21 PM

OK, I have a GTX470 with a Q9550, so a bit more than you have, with a few HDD's SSD's and 4 fans. the most o've seen my unit pulling from the wall is about 350W. idle is about 130W. 550W will be fine, its a good brand and will have good amps (which is what matters), nobody else pays this much attention, and it nearly always works. It doesn't work when they try and put a $15 POS PSU into the equation that should only be rated at 25-40% of its sold wattage. You'll be fine.
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a b ) Power supply
a b U Graphics card
January 24, 2011 10:12:34 PM

I've got a Ati5670 running without issues on my grandsons AtlonII x2 240 Compaq that only has a 250w psu. (I was surprised LoL)
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January 25, 2011 1:51:07 AM

RetiredChief: where did you find out which rails power what? Sometimes I don't know how people get to know some of the things they do..

So, basically you don't need to worry about current per rail unless it is a terrible power supply because good power supplies usually have generous max amperage per rail? I could've sworn that you had to make sure not to overload the rails. My 8800GT has a load wattage of 206 watts (http://www.anandtech.com/show/2365/13).
My Antec TruePower Trio has three 12V rails, with 18A max per rail, meaning 216 watts is the absolute max per 12V rail. However, the Antec spec page says the max wattage across all three 12V rails is 504 watts. I'm assuming the power supply is actually a single 12V rail split up into three instead of having three truly independent rails. If exceeding the 18A per rail just pulls more current from the other rails then why have the 18A max at all? ATX standards dictate that 20A is the max any rail should allow, but I know there are GPUs that are going to use more than 240 watts (see geforce 580 here: http://www.tomshardware.com/reviews/geforce-gtx-570-gf1...)

This website here: http://www.playtool.com/pages/psuconnectors/connectors.... says that the PCI-E slot in the motherboard can only provide 75 watts and that the rest of the power comes from the 6 or 8 pin molex connector. So, 75 watts plus 240 = 315, still not enough for a Geforce 570 or 580. I know that some cards actually require two PCI-E connectors so I guess that is what those cards do. However, if one rail is powering the CPU, motherboard, (PCI-E slot included), and one is powering the GPU through the 6 or 8 pin connector, then where is power for the second 6 or 8 pin connector coming from? The third 12V rail?

At this point a lot of this is just me being curious as to how this works. People in the thread have already said that without a CPU upgrade anything more than a Geforce 460 wouldn't do me a whole lot of good.
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a b ) Power supply
a b U Graphics card
January 25, 2011 2:17:49 AM

Generally you can find out which rails are which by checking some of the reviews. Sometimes the manual will state which rails are which (ie by color coded wires).

In terms of "not sweating it" basiclly yes as long as it is a "Good PSU" and You're power consumption is at least 20 % below PSU ratings, 30 % gives a little more breathing room.
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January 25, 2011 2:36:39 AM

I edited the post above a little, but I have a couple other things to discuss that are somewhat related..

I am looking at the benchmarks here: http://www.tomshardware.com/reviews/geforce-gtx-460-gf1...

and it says that with the best i7 processor, that a Geforce 460 can't even get 30 frames in Crysis (very high settings) or Alien vs. Predator (not that the game is any good from what I hear). If the card can't get more than 25 frames at 1680x1050 or 1920x1080 now, how will that card keep my computer at least at medium settings for 3 years like my 8800 has? Also, like I said, that is with a beast of an i7 processor, not some 4 year old Core 2 Duo that is being overclocked to extend its lifespan. Does anyone have an idea of how my processor would affect the benchmarks or would I have to search around and find per game benchmarks using different processors?
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a b ) Power supply
a b U Graphics card
January 25, 2011 12:44:12 PM

Then pick a GPU card that provides the performance you desire.
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February 1, 2011 11:49:32 PM

The intended topic title was "how to calculate power supply needed" and I mistyped it.

Earlier in the thread someone said that anything about a Geforce 460 would probably be limited by my processor, so I was saying that unless my processor performs well and isn't too much of a bottleneck there wouldn't be much I could to to upgrade my machine for longevity in mind without getting basically new everything.
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a b ) Power supply
a b U Graphics card
February 2, 2011 3:48:39 PM

you probably have to leapfrog your bottlenecks, so if your gpu is bottleneck by your processor, then increase processor so gpu is bottlenecked, and then increase gpu so processor is bottlenecked and repeat. The alternative is a complete system refresh every time. A bottleneck is always going to be there, there might be that fine balancing point where gpu and cpu are prefectly matched, but it willonly be under certain conditions. The leapfrog method gets away from this.

E6600 + 7900GTO > E6600 + 8800GTX > Q9550 +8800GTX > Q9550 + GTX470 > ??? + GTX470 thats been my recent path, some upgrades were opportunistic, i.e. the 7900GTO started to fail, the E6600 was passed to parents machine, but they were about when I wanted to anyway.


I know that my processor tops out in bf2bc, but my gpu is only about 60% utilised at 1680x1050, and i'm vsynch'd anyway.
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a c 144 ) Power supply
a b U Graphics card
February 3, 2011 3:55:00 PM

sgtmattbaker said:

I'm asking because I may be getting a new video card in a few months (something like the GTX 460) and I don't know if my Antec 550 TruePower Trio is going to be enough

Althought the TP3 (I have one) is advertised as a three rail PSU, disassembly and examination of the PCB indicates that it is a single rail design.

One of my systems has an OC'd Q9550, 4 GB RAM, a GTX260 - a card with similar power requirements to a GTX460, a Gigabyte EP45-UD3P motherboard, 3 hard drives (2.6 TB total) and an optical, and a Soundblaster card all powered by a Corsair 750TX.

Running 3 instances of Prime95 to load the CPU and 3DMark06 to load the GPU, it pulls 375 watts from the wall as measured by my Kill-a-Watt meter. Figuring 80% efficiency, the system pulls 300 watts from the PSU. An Antec 550 TP3 will certainly power your system with that video card.
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March 16, 2013 8:25:31 AM

sgtmattbaker said:
Well, I'll have to check to see if the Antec I have is a true three rail or not.

Anyway, where are you getting these wattage minimums for graphics cards? Some of those seem pretty high.
The numbers PSU or GFX card manufacturers tell you is likely to be high to push sales. I know a Volt times an Amp is a watt, so I guess most of what I need to know is how to determine what rail is powering what, and where to get accurate load info on graphics cards (I'm guessing the tech sheet).

Of course, I'll still have to see if my CPU is good enough to bother with a new GFX card (I have a 8800GT 512MB right now). I've got a Core 2 Duo E6600 2.4GHz overclocked to 3.15GHz, but I don't know if that will be good enough to bother getting just a new GFX card for the likes of Deus Ex: Human Revolution, Crysis 2, Batman: Arkham City, Mass Effect 3. I also just bought Battlefield Bad Company 2 so I'd like for that to look good as well.

I'm still playing games in 1280x1024, and I'm not really sure what the CPU and GPU standards are for "average" graphical quality on a 1600x1200 or 1920x1200 monitor. I have a 1920x1080 42" TV but I hear that the quality on a screen that big wouldn't be nearly as good as a dedicated monitor.


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March 16, 2013 8:28:23 AM

Probably, for sgtmattbaker the answer to "Anyway, where are you getting these wattage minimums for graphics cards?" is coming too late, but for the future readers: http://www.gpureview.com
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Best solution

a c 1202 ) Power supply
a c 564 U Graphics card
March 16, 2013 1:48:04 PM

For a system using a single GeForce GTX 460 graphics card NVIDIA specifies a minimum of a 450 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 24 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.

Overclocking of the CPU and/or GPU(s) will require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.

The Antec TruePower Trio 550 (TP3-550), with its maximum combined +12 Volt continuous current rating of 42 Amps and with two 6-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with a single GeForce GTX 460 graphics card.

During JonnyGURU.com's review of the Antec True Power Trio 650W they determined that it only has a single +12V rail since there is no OCP of 19A on each +12V rail specified on the PSU's label.

Since your Antec True Power Trio 550W is made by the same OEM (i.e. Seasonic) it only has a single +12V rail with a maximum continuous current rating of 42 Amps.
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