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Wattage Requirements

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October 13, 2011 1:34:18 AM

Hi,
I'm planning a computer build and had a question about power requirements. I was going to get two GPUs, and they both require 500 watts each. Sounds like a silly question, but would this mean I'd need a PSU larger than 1000 watts to power the whole deal? Someone told me about their build and how they used two graphics cards, both needing 500 watts, and only had a 1000 watt power supply. Wouldn't you need more than a 1000 to power both the cards and the CPU and everything else? I'm just a tad confused here, and any help would be greatly appreciated.

Thanks in advance!

More about : wattage requirements

October 13, 2011 1:51:48 AM

If you would actually tell us the GPU's in question we would be able to answer your question.

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a c 289 ) Power supply
October 13, 2011 1:55:04 AM

The wattage requirements are for the system as a whole, the 500 W recommendation includes the power needed for the CPU, motherboard, hard drives, and other components, so when you add in a second card you dont need to double the recommended power, you just need to add a bit more than the power consumption for that card. A good 750 W PSU will power most dual card setups, an 850 W power supply can power almost any dual card setup.
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October 13, 2011 1:56:42 AM

What graphics card are you planning to get? Also where are you getting the 500 watts from?
Most likely the 500 watts is for the complete system not just the graphics card.

What is more important than the wattage is the Amps on the 12v rail. You will need a good quality power supply as there are power supplies that claim they are 750w + but actually half of that.

You can take a look here for SLI GTX 580 power consumption under load.

Here is a power supply calculator to get a idea of how much power you will need. I estimate a good 850w power supply will be enough for two cards.
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October 13, 2011 1:59:22 AM

He said 500W, the only cards that use that much are the mighty Nvidia 580 or AMD 6990 Overclocked.
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October 13, 2011 2:02:40 AM

Thank you all for your replies, and I apologize, I guess it would've been easier for me to have just told you which cards I was getting. The cards I'm looking at are two Radeon HD 6950s. To be more specific, this one here:

http://www.tigerdirect.com/applications/SearchTools/ite...

I read the 500 watt requirement in the specifications, under minimum PSU wattage requirement.

Thanks again!
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a c 289 ) Power supply
October 13, 2011 2:18:18 AM

A 6950 draws about 200W of power at peak load, two of them will be pulling 400 W from the power supply, another 150 W for the CPU, 100 W for the motherboard and assorted peripherals puts you at about 650 W so a good 750 W power supply with about 60 A of current available to its 12 V rails will be plenty for that setup, definitely no need for a 1kW unit.


I know my math is kinda fudgy, but its fudged high to be on the safer side, a quick run through on the PSU calc comes to about 600W so my rough math is pretty close.
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October 13, 2011 2:20:14 AM

I just used the power supply calculator, and I already have a PSU powerful enough to run my setup. Thank you for that suggestion, Gamer-girl! I think I have all the info I need, so thank you all for your time!
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a c 289 ) Power supply
October 13, 2011 2:31:56 AM

Unfortunately no, the LSP 750 has a single 12 V rail that is only capable of providing 45 A(540 W) at most, and since the two GPUs and the CPU will need about that much that means you run the risk of overloading the unit when under full load since anything with a motor is also drawing some power from the 12 V rail.

Ultra units aren't great, they don't have quite as much power on the 12 V rail as you would like to see in a modern unit where 80% of your power used is from that rail. It might work, but it would be really close, and if that unit is more than a few years old it is less likely to be able to do it.
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October 13, 2011 2:44:33 AM

I see. Where exactly is the rail voltage listed in the specs? Looks like I'm going power supply hunting.
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October 13, 2011 3:12:45 AM

The sites will display the information differently. Some will have it in the wall of text about the power supply, others will be included in the details sections.

But usually it will have +12v then a number like 62A. This is usually the output of a quality 750w power supply. Also since you are shopping for a new power supply you might want to get a 80 plus unit with at least 4x 6-pin PCI-E connectors.

Some quality brands are antec, corsair, seasonic and XFX.
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October 13, 2011 3:43:57 AM

That is a good PSU
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October 13, 2011 4:05:25 AM

It says it has four 8/6 pin PCI-E connectors. Is this what is needed for the video cards? Are video cards typically 6 pin or 8 pin, and would this one work for either?
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October 13, 2011 4:35:51 AM

Yes that is what you will need. They are typically 6-pin but some higher end card will use a combination of a 6pin and 8pin per card.

The HX850 has 4x 6+2pin which means the connector can be used as a 6pin or if you add on the extra 2 pins it will function as a 8pin. A bit like how the big 24pin power supply cable can be separated into a 20pin with an extra 4pin.
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October 13, 2011 4:43:52 AM

Alrighty. So this one will work? It says 8/6 pin rather than 6+2... could it still be used? On the diagram on the Tiger Direct page, it looks like the PCI-E connector is one whole 8-pin connection, so I wasn't sure how that would work with a 6-pin. I just wanted to be clear.
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October 13, 2011 5:48:59 AM

It will work. That picture shows the 2pin already connected to the 6pin. Check the larger photos, it is the 7th one from the right(the end).

Or you could just look here
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a b ) Power supply
October 13, 2011 7:33:38 AM

be sure yo get the tx850 v2 which is much better and at bout the same price
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October 13, 2011 5:27:07 PM

Thank you all for your help. I think now I have enough info to make a purchase. I really appreciate all of your responses!
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October 13, 2011 5:27:57 PM

Best answer selected by camouflage212.
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