What power supply should i get for crossfire 7870

[heartless667]

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

 

[socialfox]

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=N82E16817139028


Edit: More options
http://www.newegg.com/Product/Product.aspx?Item=N82E16817182200
^ 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=N82E16817182132
^ That is another good Rosewill one.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371016

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371031

 

[bawchicawawa]

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.

 

[Guest]

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.

 

[bawchicawawa]

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.

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.

 

[socialfox]

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.

 

[bawchicawawa]

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.

 

[alexoiu]

"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_7870_2gb_reference_video_cards_in_crossfire/index16.html

 

[socialfox]

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.

 

[Guest]

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.

 

[Guest]

"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_7870_2gb_reference_video_cards_in_crossfire/index16.html

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)

 

[socialfox]

@ 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.

 

[bawchicawawa]

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.

 

[socialfox]

Let's refrain from insults, settle this like civil people...

 

[Guest]

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:

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.

 

[Guest]

@ 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.

 

[socialfox]

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?

 

[Guest]

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.

 

[socialfox]

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.

 

[heartless667]

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.

 

[socialfox]

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?

 

[heartless667]

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.

 

[socialfox]

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.

 

[heartless667]

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.

 

[socialfox]

What Rosewill model are you looking at? There are some good Rosewill power supplies and there are some bad.