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What power supply should i get for crossfire 7870

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November 11, 2012 7:45:01 PM

Hello,
i was wondering what power supply i should get for a 7870 crossfire configuration?

I have a 675w power supply right now, and i put my second 7870 in my pc, and it kept shutting off while i was playing games.

specs:
i5 3570k (stock)
amd radeon hd 7870 (stock)
8gb ram
dvd-rw drive
gigabyte ga-z77x-ud3h
nzxt phantom 410 mid tower
a b ) Power supply
November 11, 2012 7:51:18 PM

Well what brand is your current power supply? Anways I would say a good quality 550-600 watt power supply will do just fine.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...


Edit: More options
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
^ on sale and got a golden award from hardware secrets. Other rosewill power supplies aren't so good.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
^ That is another good Rosewill one.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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November 11, 2012 8:35:09 PM

I'd go with an 800w psu, for these reasons.

Gives you room to OC your cpu/both gpus.
A psu has better power efficiency when they are running on a lower %. A 600w psu at 100% load will draw more power from the wall than a 800w psu running at 75% load.
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Related resources
Anonymous
a b ) Power supply
November 11, 2012 8:48:35 PM

bawchicawawa said:
I'd go with an 800w psu, for these reasons.

Gives you room to OC your cpu/both gpus.
A psu has better power efficiency when they are running on a lower %. A 600w psu at 100% load will draw more power from the wall than a 800w psu running at 75% load.

that is so wrong!

a PSUs efficiency takes a big nose diver under 20%, about 76% in most cases. and since a rig idles more than used at full load; the money spent on getting a quality 80+ rated PSU is completely wasted.

and the difference between a 600 and 800 watt PSU, with both rated @80+ will only be a few watts, hardly enough to make up for the difference when idling. :pfff: 
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November 11, 2012 8:56:57 PM

Anonymous said:
that is so wrong!

a PSUs efficiency takes a big nose diver under 20%, about 76% in most cases. and since a rig idles more than used at full load; the money spent on getting a quality 80+ rated PSU is completely wasted.

and the difference between a 600 and 800 watt PSU, with both rated @80+ will only be a few watts, hardly enough to make up for the difference when idling. :pfff: 



You do understand 'lower' was set by the parameters of the difference between 100% and 75%, right? I wasn't talking about the 'lowest', I added context. lol =\

Anyways, the biggest reason was my first point, the second point was just a bonus depending on how much you game/fold/use bit coin, whatever else.
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a b ) Power supply
November 11, 2012 8:59:43 PM

Well I would say 800 watts would be a waste of money, an HD 7870 uses 175 watts so multiply that by 2 and you get 350 add that to a 3570k and you still get under 450 watts. Then add all those minor things like DVD drives, hard drives and fan and you will probably be around 500-550 watts. That being said 550-600 watts is more than enough. Anyways these were just rough guesses I would assume it would be less than 500 watts if someone did calculate it.
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November 11, 2012 9:10:25 PM

socialfox said:
Well I would say 800 watts would be a waste of money, an HD 7870 uses 175 watts so multiply that by 2 and you get 350 add that to a 3570k and you still get under 450 watts. Then add all those minor things like DVD drives, hard drives and fan and you will probably be around 500-550 watts. That being said 550-600 watts is more than enough. Anyways these were just rough guesses I would assume it would be less than 500 watts if someone did calculate it.


And then you include the -/+ 1ghz OC on the 3570k and the 100-200 MHZ core OC with a 150-300 mhz OC on the memory for both gpus.

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a b ) Power supply
November 11, 2012 9:14:32 PM

"Power draw at idle continues to be strong with just 200 watt is being drawn. Looking at load we do see a strong jump in power draw coming in at just over 500 watts."
The other thing to remember is that our test system is bare minimum - only a SSD hard drive is used with a single CD ROM and minimal cooling fans.
So while the system might draw 400 watts in our test system, placing it into your own PC with a number of other items, the draw is going to be higher.

http://www.tweaktown.com/articles/4597/amd_radeon_hd_78...
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a b ) Power supply
November 11, 2012 9:31:41 PM

bawchicawawa said:
And then you include the -/+ 1ghz OC on the 3570k and the 100-200 MHZ core OC with a 150-300 mhz OC on the memory for both gpus.


I don't recall that the OP stated he was overclocking, in fact he stated both his CPU and GPU was at stock clocks. Either way if he was just overclocking the CPU I believe the 600 watt power supply would do fine. If he were overclocking the GPU then I would say to increase the wattage a bit but not as much as you stated.
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Anonymous
a b ) Power supply
November 11, 2012 9:32:09 PM

bawchicawawa said:
You do understand 'lower' was set by the parameters of the difference between 100% and 75%, right? I wasn't talking about the 'lowest', I added context. lol =\

Anyways, the biggest reason was my first point, the second point was just a bonus depending on how much you game/fold/use bit coin, whatever else.

i beg your pardon, by lower you didn't set any parameters and could/would be thought of as even 5% is better than 55%. unless the specs/questions are for a bitmining or folding rig there is no reason to consider anything but normal usage; gaming hardly if ever puts nearly that amount of load on a rig . . .

however the point i made is still pertinent; looking at 100% load leads to making inappropriate decisions. a PSU should fit the system like a glove; too small or too big is no good.
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Anonymous
a b ) Power supply
November 11, 2012 9:39:34 PM

alexoiu said:
"Power draw at idle continues to be strong with just 200 watt is being drawn. Looking at load we do see a strong jump in power draw coming in at just over 500 watts."
The other thing to remember is that our test system is bare minimum - only a SSD hard drive is used with a single CD ROM and minimal cooling fans.
So while the system might draw 400 watts in our test system, placing it into your own PC with a number of other items, the draw is going to be higher.

http://www.tweaktown.com/articles/4597/amd_radeon_hd_78...

lets look at that 'test system'

that is a highly overclocked sandy-e platform that will draw more power than the OPs rig. (and by a substantial margin of ~50 watts)
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a b ) Power supply
November 11, 2012 9:45:28 PM

@ looniam, what would you say is the power supply wattage needed for this build? I am sure the OP will be a bit confused seeing how there are different answers.
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November 11, 2012 9:54:30 PM

Anonymous said:
i beg your pardon, by lower you didn't set any parameters and could/would be thought of as even 5% is better than 55%. unless the specs/questions are for a bitmining or folding rig there is no reason to consider anything but normal usage; gaming hardly if ever puts nearly that amount of load on a rig . . .

however the point i made is still pertinent; looking at 100% load leads to making inappropriate decisions. a PSU should fit the system like a glove; too small or too big is no good.


I beg your pardon. I set the perimeters in the sentence after it, the full thought consisted of 2 sentences.

Also, If you knew how to read and not cherry pick, I said that it's a bonus, NOT the real reason to pick a 800w psu for crossfire 7870's and a 3570k.

Not my fault you are terrible at comprehending the English language, sir.
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a b ) Power supply
November 11, 2012 10:03:57 PM

Let's refrain from insults, settle this like civil people...
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Anonymous
a b ) Power supply
November 11, 2012 10:27:00 PM

bawchicawawa said:
I beg your pardon. I set the perimeters in the sentence after it, the full thought consisted of 2 sentences.

Also, If you knew how to read and not cherry pick, I said that it's a bonus, NOT the real reason to pick a 800w psu for crossfire 7870's and a 3570k.

Not my fault you are terrible at comprehending the English language, sir.

ok lets look at that:
Quote:
A 600w psu at 100% load will draw more power from the wall than a 800w psu running at 75% load.


where is the rated efficiency for both PSUs? or are assuming both PSUs have the exact rating for each? that doesn't happen. a bronze 600 would use less wattage from the wall as opposed to an 80+ rate 800 watt.

as i said, when considering idle power load whatever differences there would be under a 600 watt load would be negated.

and you really need to apologize for that comprehending english comment. that was completely out of line and if you cannot have a discussion without being insulting, learn to grow up.
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Anonymous
a b ) Power supply
November 11, 2012 10:39:58 PM

socialfox said:
@ looniam, what would you say is the power supply wattage needed for this build? I am sure the OP will be a bit confused seeing how there are different answers.

theoretically a 600 watt PSU would be fine BUT it helps to have four 6 pin PCI power connections.

XFX Core Edition PRO650W $89.99
$79.99 after $10.00 rebate card

on a side note, i saw one of your suggestions was my PSU - it has a 6 and 6+2 connections. however knowing the quality of it, i would not hesitate to use two 6 pin adapters. but i wouldn't make it a suggestion to others. its a liability thing - if something goes flonky, i'd hate to see it affect someone else.
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a b ) Power supply
November 11, 2012 10:49:48 PM

Well makes sense to have 650 watts to be on the safe side :lol: 
Didn't realize the HD 7870's require two pci-e connectors, if I had known that I would have chosen a power supply with four pci-e connectors. Nice work in bringing that up, anyways don't they include the adapters for free with most video cards?
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Anonymous
a b ) Power supply
November 11, 2012 11:11:05 PM

yeah and those adapter can be a problem. to be cautious its better to plug them into separate strings of the 4 pin molex; most PSUs have two strings of molex connections.

to use two, that means they each share or have both adapters connected to a single string. if it is a cheap power supply and they used a thinner wire, then the resistance will put a higher load on the POS PSU and also starve the card of power.

i would not hesitate to suggest a person using ONE but for two . . like i said, i would do it myself but i would generally not advise it.
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a b ) Power supply
November 11, 2012 11:16:12 PM

Makes sense, I got input from a friend of mine (mocchan, a top forum contributor) and he said that 600-650 watts would be optimal for this build. I guess we can safely say the XFX Core Edition 650 watts is the optimal power supply for this build since it has 4 pci-e connectors.

Anyways nice talking to you, even I learned something new from you today even though this was not my thread. :) 
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November 13, 2012 7:32:55 PM

I have a thermaltake 675w. It's a 80 plus bronze, so i guess i should upgrade then? I tried playing the witcher 2, and it froze and my computer had to be restarted. It was acting strange, and i saw no performance gain whatsoever on any games, even though i had two 7870.
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a b ) Power supply
November 13, 2012 7:35:34 PM

How old is that power supply? Generally I stay away from Thermaltake power supplies but the toughpower series seem to get real good reviews. Anyways not sure why exactly it isn't working out for you. Do you have any other hardware that you have not listed that draws a lot of watts?
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November 13, 2012 7:50:14 PM

No, i don't think i have a whole lot of hardware that draws a lot of power. The power supply is maybe two weeks old, if that. This is my first build, and i'm still pretty new to it.
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a b ) Power supply
November 13, 2012 7:55:01 PM

Might be a defective power supply? If it has been only 2 weeks from the day you bought it before buying a completely new power supply I would urge you to RMA it and try out a replacement. If you did buy it brand new then you should have warranty.
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November 14, 2012 7:14:02 PM

Yeah, i do have my 30 day guarantee through newegg still. It does sound defective. I'm looking at a rosewill 1000w 80 plus gold power supply, just to give me ALOT of room to upgrade, but it's on sale for 129.99 on Newegg.
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a b ) Power supply
November 14, 2012 7:19:47 PM

What Rosewill model are you looking at? There are some good Rosewill power supplies and there are some bad.
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November 14, 2012 7:45:48 PM

Oh wow, that's only 120 on amazon too. That works because amazon doesn't charge tax =). Thanks, man. Oh, and call me a noob, but can you explain the whole pci-e slot deal, where on my motherboard i have a x16 slot, but when i put two video cards in there they both drop down to x8. What does that mean? Does it mean they'll have the same performance as one graphics card but with just two gpu's. I have pci-e 3.0.
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a b ) Power supply
November 14, 2012 7:56:04 PM

Haha, glad there was a labelled picture already. Anyways look below:
http://www.gigabyte.com/fileupload/LineImage/2/4153/588...

Anyways I'm just taking a guess but the x16 slot is the first one, and the x8 should be the one below it. For crossfire/sli just use the first two slots.

I copied this from the GIGABYTE Website and so I take no credit for the work:

" 1 x PCI Express x16 slot, running at x16 (PCIEX16)
* For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot.

1 x PCI Express x16 slot, running at x8 (PCIEX8)
(The PCIEX16 and PCIEX8 slots conform to PCI Express 3.0 standard.)
* The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When the PCIEX8 slot is populated, the PCIEX16 slot will operate at up to x8 mode.
* PCIE Gen.3 is dependent on CPU and expansion card compatibility.

1 x PCI Express x16 slot, running at x4 (PCIEX4)
* The PCIEX4 slot shares bandwidth with all PCI Express x1 slots. All PCI Express x1 slots will become unavailable when a PCIe x4 expansion card is installed.

3 x PCI Express x1 slots
(The PCIEX4 and PCI Express x1 slots conform to PCI Express 2.0 standard.)

1 x PCI slot "

Here is the original link:http://ca.gigabyte.com/products/product-page.aspx?pid=4...

Anyways the crossfired/SLIed cards wont have the same performance of a single card (in the same class). They would be better.

Edit: If you are not catching on then the PCI-E slots are the long ones with the fin thing at the end :lol: 
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November 14, 2012 7:59:46 PM

Anonymous said:
ok lets look at that:
Quote:
A 600w psu at 100% load will draw more power from the wall than a 800w psu running at 75% load.


where is the rated efficiency for both PSUs? or are assuming both PSUs have the exact rating for each? that doesn't happen. a bronze 600 would use less wattage from the wall as opposed to an 80+ rate 800 watt.

as i said, when considering idle power load whatever differences there would be under a 600 watt load would be negated.

and you really need to apologize for that comprehending english comment. that was completely out of line and if you cannot have a discussion without being insulting, learn to grow up.

with a cheap psu sure, to an extent.

Most psu peak efficiency at 50% load. That 600 W will pull more power at 600W than the 800W at 600W load if they have the same rating.

http://www.anandtech.com/show/5707/corsair-tx550m-vs-oc...

The big advantage to high power, high quality psu is your idle efficiency is even greater, negating your idle power costs.

http://www.anandtech.com/show/3992/1000w1200w-highend-p...

middle of the road 550W corsair psu- 70-75% efficient at idle, OCZ 1000W, 83% at idle.

How is too much PSU a bad thing, they are generally more efficient, you won't be stressing it out, leading to less likely for a PSU blowout, and generally nearing 100% load gives crappy voltage ripple, and you will likely never need to buy another psu even if you decide to add a 3rd 7950, or a 4th 7950.
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November 14, 2012 8:08:16 PM

Oh no, i know where the pci-e slots are lol. I meant like what does it mean when you add a second video card, and the x16 slot drops down to x8 along with the second pci-e slot. Because my motherboard only has one x16 slot, and the others are x8, and x4 for the third one. But if i'm only using one video card then the x16 slot stays x16, but if i add another video card then they both slots drop down to x8 apparently.
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November 14, 2012 8:09:27 PM

Oh wait, i think i understand now lol. I reread that, and it makes sense now.
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November 14, 2012 8:47:03 PM

I'm no expert on PSUs, dont know particulars they use inside and therefore the differences. However noone mentioned OCZ's...
I'm using OCZ on my system and i could recommend that. Very stable, didnt change a Voltage in over 3 years, quite and didnt get hot or fail in any way.

I'm using Phenom II 965 BE, GTX560Ti, OCZ modXstream pro 600W

From my experience i would recommend that, i do install them in my business building PCs and noone complaint yet :) 

Good luck with your build
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Anonymous
a b ) Power supply
November 14, 2012 9:02:53 PM

noob2222 said:
with a cheap psu sure, to an extent.

Most psu peak efficiency at 50% load. That 600 W will pull more power at 600W than the 800W at 600W load if they have the same rating.

http://www.anandtech.com/show/5707/corsair-tx550m-vs-oc...

The big advantage to high power, high quality psu is your idle efficiency is even greater, negating your idle power costs.

http://www.anandtech.com/show/3992/1000w1200w-highend-p...

middle of the road 550W corsair psu- 70-75% efficient at idle, OCZ 1000W, 83% at idle.

How is too much PSU a bad thing, they are generally more efficient, you won't be stressing it out, leading to less likely for a PSU blowout, and generally nearing 100% load gives crappy voltage ripple, and you will likely never need to buy another psu even if you decide to add a 3rd 7950, or a 4th 7950.

dude!

there are A LOT of holes in your argument right there.

first the difference in efficiency between 50% and 80% load is so relatively minor its negligible (2%-3% usually and whats that? 0.1 watt?)

you are comparing a low watt 80+ certified PSU to a gold rated PSU of course there will be a large difference in low load efficiency. not a level field of comparison what so ever.

ripple and noise on any rail has absolutely NOTHING to do with how much load is on the PSU but the quality of the components. to say a higher wattage PSU is more efficient is complete nonsense . . . :heink: 

edit: btw, your link shows what i have been saying, see that 7% efficiency drop off under 20% load ? (84%/83% for 230/115vac) so buy a high wattage gold rated PSU and get the efficiency of a 80+ PSU? yeah makes sense all right . . . :p 

no, the OP would be better off buying a more appropriate 650-750 watt bronze rated PSU for $80 than get a $120 gold rated 1K PSU for overall efficiency for idle and load.
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November 14, 2012 9:21:39 PM

Anonymous said:
dude!

there are A LOT of holes in your argument right there.

first the difference in efficiency between 50% and 80% load is so relatively minor its negligible (2%-3% usually and whats that? 0.1 watt?)

you are comparing a low watt 80+ certified PSU to a gold rated PSU of course there will be a large difference in low load efficiency. not a level field of comparison what so ever.

ripple and noise on any rail has absolutely NOTHING to do with how much load is on the PSU but the quality of the components. to say a higher wattage PSU is more efficient is complete nonsense . . . :heink: 

might want to do some more homework then.

http://www.hardwaresecrets.com/article/Rosewill-SilentN...

12v ripple.
Test 1, 104W 10mv
Test 2, 210W, 14mv
test 3, 314W, 20mv
Test 4, 425W, 27mv
Test 5, 520W, 33mv

really, ripple doesn't go up ... not at all ... and this is on a 90% efficient psu. Cheap psu ripple gets absolutely out of control at 100% load. http://www.hardwaresecrets.com/article/Thermaltake-Smar...

72mv ripple at full load ... but only 21mv at 286W, 36mv at 430w, nearly the same as the roswill at that point. ya, ripple doesn't have anything to do with the load.

FWIW 2% at 600W is 12, not 0.1
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Anonymous
a b ) Power supply
November 14, 2012 9:32:33 PM

noob2222 said:
might want to do some more homework then.

http://www.hardwaresecrets.com/article/Rosewill-SilentN...

12v ripple.
Test 1, 104W 10mv
Test 2, 210W, 14mv
test 3, 314W, 20mv
Test 4, 425W, 27mv
Test 5, 520W, 33mv

really, ripple doesn't go up ... not at all ... and this is on a 90% efficient psu. Cheap psu ripple gets absolutely out of control at 100% load. http://www.hardwaresecrets.com/article/Thermaltake-Smar...

72mv ripple at full load ... but only 21mv at 286W, 36mv at 430w, nearly the same as the roswill at that point. ya, ripple doesn't have anything to do with the load.

FWIW 2% at 600W is 12, not 0.1

i'll admit i didn't use the best terms in explaining that.
yes ripple will increase though how much ripple there is does depend on the quality of components.

but getting back to the low load, from your article:
http://www.anandtech.com/show/3992/1000w1200w-highend-p...

a FIFTEEN PERCENT drop in efficiency from 20% to 10% load. (90%-75%)

again shows it is not wise to buy a high quality over kill of a PSU.
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