7850 Crossfire - Will it run on a 550w Power Supply?

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richaron

Golden Member
Mar 27, 2012
1,357
329
136
at stock he would be fine but he is ocing his cards by 40% with higher voltages and ocing his cpu so that changes everything. that could easily pull fairly close to 500 watts which is not a good idea for long term use IMO.

I'd eat my shirt if he can make his system use >500W while gaming (on 24/7 timings). Should still fall into the <90% efficiency range & only stress psu a few hours a day.
 
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toyota

Lifer
Apr 15, 2001
12,957
1
0
eat my shirt if he can make his system use >500W while gaming (on 24/7 timings)
how much power does a 7850 with a 40% oc and additional voltage use? it would probably use way more power than a stock 7870 which uses about 130 watts just in games. I would guess at least 160 watts in demanding for a very highly oced 7850 with more voltage. that means about 320 watts just in demanding games for only the cards. throw in the oced cpu and the rest of the components and I could easily see fairly close to 500 watts peaks in very demanding games and an additional 50 watts or more in a heavy stress test. of course this is only guess but unless someone has some figures for highly oced 7850 cards then better to be really safe.
 
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jacktesterson

Diamond Member
Sep 28, 2001
5,493
3
81
how much power does a 7850 with a 40% oc and additional voltage use? it would probably use way more power than a stock 7870 which uses about 130 watts just in games. I would guess at least 160 watts in demanding for a very highly oced 7850 with more voltage. that means about 320 watts just in demanding games for only the cards. throw in the oced cpu and the rest of the components and I could easily see fairly close to 500 watts peaks in very demanding games and an additional 50 watts or more in a heavy stress test. of course this is only guess but unless someone has some figures for highly oced 7850 cards then better to be really safe.

Will know soon enough since I am awaiting a kill-a-watt from Newegg


Also, I know the 1000w PSU is overkill, but I already own it. Not much point in selling at a loss to buy a smaller unit.
 

toyota

Lifer
Apr 15, 2001
12,957
1
0
Will know soon enough since I am awaiting a kill-a-watt from Newegg


Also, I know the 1000w PSU is overkill, but I already own it. Not much point in selling at a loss to buy a smaller unit.
I sure would not trust my system on solely on what the kill-a-watt says. I have seen two different units report wildly different power usage.
 

dualsmp

Golden Member
Aug 16, 2003
1,626
44
91
Will know soon enough since I am awaiting a kill-a-watt from Newegg


Also, I know the 1000w PSU is overkill, but I already own it. Not much point in selling at a loss to buy a smaller unit.

I predict you'll see a little over 400w from the wall (I doubt more than 450w). A 550w PSU should be enough.
 

blckgrffn

Diamond Member
May 1, 2003
9,111
3,029
136
www.teamjuchems.com
how much power does a 7850 with a 40% oc and additional voltage use? it would probably use way more power than a stock 7870 which uses about 130 watts just in games. I would guess at least 160 watts in demanding for a very highly oced 7850 with more voltage. that means about 320 watts just in demanding games for only the cards. throw in the oced cpu and the rest of the components and I could easily see fairly close to 500 watts peaks in very demanding games and an additional 50 watts or more in a heavy stress test. of course this is only guess but unless someone has some figures for highly oced 7850 cards then better to be really safe.

I agree with you.

The trick is a sustained GPU and CPU load. If he fired up a DC app like PrimeGrid w/AVX and GPU clients, I would be surprised if he wasn't pushing the overload protection on that PSU.

Now, just for playing games? It might enough new... but after some degradation? Why trust that much investment to a just "right sized" PSU?
 

RigRebel

Junior Member
May 27, 2012
5
0
0
I've skimmed through most the replies and what I haven't seen anyone say (although I could have missed it) is that for high graphics video card, and PSU combinations, the most often overlooked but most crucial thing to look at is REQUIRED/PROVIDED AMPERAGE. Let me explain, you can have 2 500 watt powers supplies side by side, one with crappy 18amps total continuous amperage and the other with good 24-30Amp continuous amperage. If the card, in this case the 7850, requires @22amps at full load (which it does see calculations below in point 2.) then the card will work fine at full load with 24-30Amp powers supply and random reboot at full load on the 18Amp powersupply when power draw goes up during gaming load. AND THEY ARE BOTH 500w POWERSUPPLIES SO YOU CAN'T GO ON WATTAGE ALONE. Likewise, you can buy a nice Seasonic x650 with Gold efficency and "Crossfire certified" BUT with only 54amps on a single 12v and that's NOT going to run 2 OC'd 7850s in Xfire because as calculated below you're gonna want AT LEAST 60amps total. Thus, the only thing you'll Xfire is 2 weaker cards like 7770s OR 2 low power (single fan small cards) 7850s at STOCK clocks. Most people you ask about OCing a video card as it relates to power draw will talk in "watts" but what they are missing (or not clarifing) is that watts relate to AMPS and the AMPS is what you really want from your PSU for nice gaming video cards and OCing. Read below (2).

IMPORTANT THINGS TO KNOW:
1. You want a single 12V rail if your going for gaming and gaming video cards, they are more efficent and no power loss/drop off the rail. For more on that go to hardwaresecrets.com and read their tutorial on "The Anatomy of Switching Powersupplies" http://www.hardwaresecrets.com/article/327 it's excellent! The dual 12v Rails are more for servers IMO because if one rail fails the psu will still limp along over night till it's replaced in the morning. If it's in a game rig, and you loose a rail, you're probably gonna reboot anyways because it won't be able to handle the amperage with only one rail working in a dual rail powersupply thus it will just reboot and you'll be replacing it and it won't really limp you through the night anyways.

2. Depending on the review/and card you pick, the average Radeon 7850 TPD (total power draw) seems to draw between 222Watts and 274 Watts at full load for the more efficent cards like the powercolor, diamond and VisionTek. These are all single fan models. We're not concerned with idle power draw in this calculation cause you're not going to play BF3, Skyrim, SWTOR, D III or anything else at idle lol! Now here's the important part based on that info. Watts divided by Volts = amps. In mathimatical form, W/V=Amps. So, 222W/12v = 18.5 amps and 274W/12v = 22 amps. That's your average required amperage for the above mentioned styles 7850. Now this does not take into account leakage, efficency etc etc.. but it is a good general basis that says on REFERENCE CLOCKS (what the card comes set at) at full load you'll need at least 22amps... And, since digging around on the net can produce AMD material that states the older 6850 required 24amps minium, 22 amps for the newer less power hunger 7850s sounds legit... Also, that's at REFERRENCE clocks .. if you over clock you're gonna want some head room so I would suggest a MINIMUM of 30amps on a single 12V rail as a good starting point for a powersupply. You can find 30amp 12V 550 watts all over newegg and I've got one from UlTRA a 550W LSP myself (although efficency drops after a year).

SO, to answer your question, YES it will work on a 500W powersupply PROVIDED it has atleast 22Amps minimum; but, at miniumum expect it to reboot if it's older or less efficent, especially if you pack in a bunch of Hard-drives because sata drives can also share the 12v rail. To be safe I'd check to make sure you have AT LEAST a nice 30amp single 12v PSU, especially if you want to OC, if not buy a new one... Might I suggest this one > http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013 It's 44amps but cheaper than the 500watt ones with the criteria of single 12 rail and active PFC. You can check your current powersupply either by manufacturer's webpage, the box or the label on the PSU it self. Look for the +12V box on the grid... I should say "30A" miniumum to be safe because the hard-drives ALSO share power with the 12v rail; and, to allow headroom for ocing and decline in efficency over it's life span.

Personally, if you're going to OC + OV and Xfire, I'd go with a 70Amp 850W MINIUM powersupply like the XXX PRO 850 from XFX that's built similar in design to Seasonic and by the same parent manufacturer that builds both; but, the XFX XXX PRO 850 is about $40-$50.00 cheaper. Also, at 70amps that gives you 5amps per card headroom over OC minimum of 30amps per card AND that's CONTINUOUS RATING.. the max amperage will probably be around 86Amps but that's not sustainable. For an echo effect > if you plan to OC+OV and XFire get at least a 850W gold/silver PSU with proper connections and be done with it. :) http://www.newegg.com/Product/Produc...82E16817207017

REMEMBER > AMPERAGE IS KEY! Ignore the post for wattage draw "from the wall" lol because (you'll most likely under amp the card and it will run fine at idle then reboot at load) they are going by what the PSU draws and that's not what you want...You want WHAT THE VIDEO CARD DRAWS and the key to that is AMPERAGE. "Wattage from the wall " calculations is what you get when you let an electrician pick your powersupply and not a PC hardware specialist or tech lol. Again, You can have one 500Watt psu at 18amps and one 500W psu at 24-30amps and the one with higher amps (provided it meets the minium required by the video card to run at load) will run your card at full load the 18amp one WILL reboot just when you're getting your frag on ... lol. For OCing add about 8-10amps headroom. Trust me I used to sell new powersupplies with high end video cards all day long because customers didn't know the difference between wattage and amperage and what to look at most in a PSU for higher end gaming cards... the answer = amperage. I pick ALL my PSUs for gaming rigs based on AMPERAGE, Single 12v Rail, Electric Signal Noise, Max load and Efficency and the most important factors to me above all is 1. Single 12V Rail 2. Amperage. The rest is icing.

Welcome to the wonderful (and expensive) world of properly suppling power to a good video card and over clocking. Good luck :)
 
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bononos

Diamond Member
Aug 21, 2011
3,883
142
106
I predict you'll see a little over 400w from the wall (I doubt more than 450w). A 550w PSU should be enough.

But many users including myself prefer more headroom to keep noise levels down since the psu fan doesn't have to spin at full speed all the time if at all.
 

postmortemIA

Diamond Member
Jul 11, 2006
7,721
40
91
I got kill-a-watt. And a single 7850. Rest of PC is in sig. Q9650 has TDP of 95W. Kill-A-Watt shows max 400W usage under heavy load (furmark). This includes speakers and 27" monitor. I think 550W will be okay, but your PSU might get noisy, and that fan on it draws more power under load too.
 
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lehtv

Elite Member
Dec 8, 2010
11,900
74
91
postmortemIA what's your PSU, and did you OC the q9650 and/or the 7850?

Monitors and speakers aren't powered from the PSU...
 

jacktesterson

Diamond Member
Sep 28, 2001
5,493
3
81
I've skimmed through most the replies and what I haven't seen anyone say (although I could have missed it) is that for high graphics video card, and PSU combinations, the most often overlooked but most crucial thing to look at is REQUIRED/PROVIDED AMPERAGE. Let me explain, you can have 2 500 watt powers supplies side by side, one with crappy 18amps total continuous amperage and the other with good 24-30Amp continuous amperage. If the card, in this case the 7850, requires @22amps at full load (which it does see calculations below in point 2.) then the card will work fine at full load with 24-30Amp powers supply and random reboot at full load on the 18Amp powersupply when power draw goes up during gaming load. AND THEY ARE BOTH 500w POWERSUPPLIES SO YOU CAN'T GO ON WATTAGE ALONE. Likewise, you can buy a nice Seasonic x650 with Gold efficency and "Crossfire certified" BUT with only 54amps on a single 12v and that's NOT going to run 2 OC'd 7850s in Xfire because as calculated below you're gonna want AT LEAST 60amps total. Thus, the only thing you'll Xfire is 2 weaker cards like 7770s OR 2 low power (single fan small cards) 7850s at STOCK clocks. Most people you ask about OCing a video card as it relates to power draw will talk in "watts" but what they are missing (or not clarifing) is that watts relate to AMPS and the AMPS is what you really want from your PSU for nice gaming video cards and OCing. Read below (2).

IMPORTANT THINGS TO KNOW:
1. You want a single 12V rail if your going for gaming and gaming video cards, they are more efficent and no power loss/drop off the rail. For more on that go to hardwaresecrets.com and read their tutorial on "The Anatomy of Switching Powersupplies" http://www.hardwaresecrets.com/article/327 it's excellent! The dual 12v Rails are more for servers IMO because if one rail fails the psu will still limp along over night till it's replaced in the morning. If it's in a game rig, and you loose a rail, you're probably gonna reboot anyways because it won't be able to handle the amperage with only one rail working in a dual rail powersupply thus it will just reboot and you'll be replacing it and it won't really limp you through the night anyways.

2. Depending on the review/and card you pick, the average Radeon 7850 TPD (total power draw) seems to draw between 222Watts and 274 Watts at full load for the more efficent cards like the powercolor, diamond and VisionTek. These are all single fan models. We're not concerned with idle power draw in this calculation cause you're not going to play BF3, Skyrim, SWTOR, D III or anything else at idle lol! Now here's the important part based on that info. Watts divided by Volts = amps. In mathimatical form, W/V=Amps. So, 222W/12v = 18.5 amps and 274W/12v = 22 amps. That's your average required amperage for the above mentioned styles 7850. Now this does not take into account leakage, efficency etc etc.. but it is a good general basis that says on REFERENCE CLOCKS (what the card comes set at) at full load you'll need at least 22amps... And, since digging around on the net can produce AMD material that states the older 6850 required 24amps minium, 22 amps for the newer less power hunger 7850s sounds legit... Also, that's at REFERRENCE clocks .. if you over clock you're gonna want some head room so I would suggest a MINIMUM of 30amps on a single 12V rail as a good starting point for a powersupply. You can find 30amp 12V 550 watts all over newegg and I've got one from UlTRA a 550W LSP myself (although efficency drops after a year).

SO, to answer your question, YES it will work on a 500W powersupply PROVIDED it has atleast 22Amps minimum; but, at miniumum expect it to reboot if it's older or less efficent, especially if you pack in a bunch of Hard-drives because sata drives can also share the 12v rail. To be safe I'd check to make sure you have AT LEAST a nice 30amp single 12v PSU, especially if you want to OC, if not buy a new one... Might I suggest this one > http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013 It's 44amps but cheaper than the 500watt ones with the criteria of single 12 rail and active PFC. You can check your current powersupply either by manufacturer's webpage, the box or the label on the PSU it self. Look for the +12V box on the grid... I should say "30A" miniumum to be safe because the hard-drives ALSO share power with the 12v rail; and, to allow headroom for ocing and decline in efficency over it's life span.

Personally, if you're going to OC + OV and Xfire, I'd go with a 70Amp 850W MINIUM powersupply like the XXX PRO 850 from XFX that's built similar in design to Seasonic and by the same parent manufacturer that builds both; but, the XFX XXX PRO 850 is about $40-$50.00 cheaper. Also, at 70amps that gives you 5amps per card headroom over OC minimum of 30amps per card AND that's CONTINUOUS RATING.. the max amperage will probably be around 86Amps but that's not sustainable. For an echo effect > if you plan to OC+OV and XFire get at least a 850W gold/silver PSU with proper connections and be done with it. :) http://www.newegg.com/Product/Produc...82E16817207017

REMEMBER > AMPERAGE IS KEY! Ignore the post for wattage draw "from the wall" lol because (you'll most likely under amp the card and it will run fine at idle then reboot at load) they are going by what the PSU draws and that's not what you want...You want WHAT THE VIDEO CARD DRAWS and the key to that is AMPERAGE. "Wattage from the wall " calculations is what you get when you let an electrician pick your powersupply and not a PC hardware specialist or tech lol. Again, You can have one 500Watt psu at 18amps and one 500W psu at 24-30amps and the one with higher amps (provided it meets the minium required by the video card to run at load) will run your card at full load the 18amp one WILL reboot just when you're getting your frag on ... lol. For OCing add about 8-10amps headroom. Trust me I used to sell new powersupplies with high end video cards all day long because customers didn't know the difference between wattage and amperage and what to look at most in a PSU for higher end gaming cards... the answer = amperage. I pick ALL my PSUs for gaming rigs based on AMPERAGE, Single 12v Rail, Electric Signal Noise, Max load and Efficency and the most important factors to me above all is 1. Single 12V Rail 2. Amperage. The rest is icing.

Welcome to the wonderful (and expensive) world of properly suppling power to a good video card and over clocking. Good luck :)


Thread was done 5 weeks ago :)
 

postmortemIA

Diamond Member
Jul 11, 2006
7,721
40
91
postmortemIA what's your PSU, and did you OC the q9650 and/or the 7850?

Monitors and speakers aren't powered from the PSU...
I shall have clarified that I have put kill-a-watt on the outlet, so it was measuring consumption of the whole system, including the speakers and monitor. These two consume at least 100W.

PSU is Corsair 600W Gaming Series. Any 80Plus is going to draw similar amount of power.

Nothing is overclocked. consumption for the whole system ranges from 200 to 400W. Radeon 7850 does not consume much in idle state, it has clocks 300 and 150MHz.
 

lehtv

Elite Member
Dec 8, 2010
11,900
74
91
I shall have clarified that I have put kill-a-watt on the outlet, so it was measuring consumption of the whole system, including the speakers and monitor. These two consume at least 100W.
Why not put the kill-a-watt to the socket on your splitter that powers only the PC...?

Anyway if we take 100W for the monitor and speakers, that leaves 300W from the wall which is just 300 * 0.8 = 240W DC. Add a second 7850 = ~350W total, easily and I mean truly easily managed by a 550W unit
 
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p_monks33

Golden Member
May 22, 2011
1,292
5
81
I was running an I5 2500k at 4.5ghz and CF 6850 Asus DirectCU's that were clocked at 1000mhz Core and 1120mhz memory on a Corsair GS600 I never had a problem. Don't the 7850's draw considerably less juice?
 

2is

Diamond Member
Apr 8, 2012
4,281
131
106
OC'd 2500K = 150W max, <100W light load / gaming
7850 = 110W
7850 = 110W
the rest = 50W

420W max load, of course a rough estimate but under 80% of 550W.

Except most of that load is on the 12v rail and not all of the 550 watts is. ;)
 

postmortemIA

Diamond Member
Jul 11, 2006
7,721
40
91
Except most of that load is on the 12v rail and not all of the 550 watts is. ;)

OCZ claims you can use up to 550W from 12V rail
http://www.ocztechnology.com/res/manuals/OCZ_ZT_PSU_Product_Sheet.pdf

EDIT.
I did some consumption testing where kill-a-watt is connected directly to the PSU (corsair 600W GS), here are the numbers:
lowest idle consumption : 101W
max load consumption: 260W

Thus, I don't see how 2 7850s cannot be supported by a good 550W PSU.
 
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jacktesterson

Diamond Member
Sep 28, 2001
5,493
3
81
Hi Guys,

Just so you all know, I had the 2nd 7850 weeks ago, played with it, and sent it back. Crossfire is a mess right now and I was happy with performance of one.

I can tell you that I did try my ZT 550w with it just to play around, and It worked fine for benchmarking.

The ZT series from OCZ can run its full wattage from the 12v rail. They are really solid budget PSU's. (coming from somebody who refused to touch a OCZ PSU for most part before)
 
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lehtv

Elite Member
Dec 8, 2010
11,900
74
91
Except most of that load is on the 12v rail and not all of the 550 watts is. ;)

ZT550 actually has a +12V output rated for 45A * 12V = 540W. Going by that and the numbers in my earlier post (#23), the +12V rail will be stressed by less than 70% in full CPU+GPU load (no OC on the GPUs)
 
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lehtv

Elite Member
Dec 8, 2010
11,900
74
91
I am confused about how to figure out the amperage. I just ordered the same setup, 2 x 7850 CF and I have this 550w PS:
http://kingwin.com/products/cate/power_supplies/lzg_550.asp

9bMZH.png


That PSU will run 7850 CF easily.
 

BFG10K

Lifer
Aug 14, 2000
22,674
2,824
126
Except most of that load is on the 12v rail and not all of the 550 watts is.
Any decent PSU can output pretty much all of its rated wattage on the 12V. All of the good ones only have a 12V rail anyway, with a DC-DC converter to handle the minor rails.