Can my PSU support Crossfire?

[UsernameLadiesMan217]

I have the Antec HCG 620 - http://store.antec.com/Product/power_supply-high_current_gamer/hcg-620/0-761345-23860-1.aspx

I was thinking of running Radeon 7850's in Crossfire.

How can I tell if my PSU will support this?

 

[wizardofid]

260 odd watts about 21 amps, pending how the rest of the system looks like, and you have enough PCI-e connectors without having to add any extra molex to PCi-e cables and age of PSU. There shouldn't be any short term problems.

However take note that Ocing CPU and over GPU's would be completely out of the question.

 

[UsernameLadiesMan217]

260 odd watts about 21 amps, pending how the rest of the system looks like, and you have enough PCI-e connectors without having to add any extra molex to PCi-e cables and age of PSU. There shouldn't be any short term problems.

However take note that Ocing CPU and over GPU's would be completely out of the question.

idk if I have enough connectors, it's not molex.

rest of system is

i3 2120
regular mobo
8gb ddr3 ram
1 optical drive
1 hdd
4 usb
4 fans


PSU calcs tell me I need a PSU with 383 watts to run it (if I add 2 gpu's), but I know that the number tends to need a 100 watt buffer.

idk...

 

[Pada]

Why do you want to go for a CrossFire setup?
That i3 will be the bottleneck with a single HD7850 already, so its quite pointless to get another, unless you're going to play a game that requires virtually no CPU power.

 

[UsernameLadiesMan217]

Why do you want to go for a CrossFire setup?
That i3 will be the bottleneck with a single HD7850 already, so its quite pointless to get another, unless you're going to play a game that requires virtually no CPU power.

Going to replace the i3 and mobo (maybe) eventually, just learning as much as I can atm.

 

[Pada]

Going to replace the i3 and mobo (maybe) eventually, just learning as much as I can atm.

The HD 7850 requires only 1x 6-pin PEG connector for power, which mean that the HCG 620 should suffice, seeing that it has 2x 6+2-pin PEG connectors. Also, the HD 7850 won't draw more than 110W, unless you're going to overclock the card and run FurMark.

I would however recommend that you rather opt for a single higher spec'd graphics card than going for a dual graphics card setup!

The only reasons why I opted to go for 2x GTX460's long ago was:
1) 2x GTX460's was cheaper than 1x GTX480, and it outperformed it by a big margin in most cases + I already had 1x GTX460 to start with
2) I already had a high end system that supported SLI
3) Dual graphics cards look awesome

Dual graphics card setups would require that your motherboard support SLI/CrossFire.
You can also run into heat problems when the motherboard's 16x PCIe slots doesn't have other PCI/PCIe slots inbetween to leave a 1-2x slot gap between the graphics cards. For optimal cooling, you'll also require a large enough case to provide good airflow.
Your performance/watt is generally worse in a dual graphics card setup and you are likely to have issues in games that weren't developed to make use of dual graphics card setups. So you generally need a pretty big PSU for a dual GPU setup compared to a single GPU one.

So ja, those are just a couple of reasons why I'd advise to stick to a single GPU.

 

[wizardofid]

@ Pada
No the stock power draw on a 7850 is 130watts not 110. Even at 130watts there shouldn't be heat problems, side panel fan is more than capable to removing trapped air, and it is winter.However the stuff that you mention is minor compared to the second slot only running at x4, considering he mentioned it was a regular board

Games are not directly coded for dual GPU's, that is what the DX API and display drivers are for to handle that.

Secondly I3 is hardly a bottle neck for 2 x 7850's the fact is, 7850 isn't even capable of running at a 3rd of the PCI-e bandwidth, no amd 7 series card is capable of using the full allocated bandwidth.In gaming at least, with mining over all bandwidth bus usages is considerably better however it still doesn't make use of all allocated bandwidth.

Quad and tri sli have better results using bandwidth allocated.

 

[UsernameLadiesMan217]

The HD 7850 requires only 1x 6-pin PEG connector for power, which mean that the HCG 620 should suffice, seeing that it has 2x 6+2-pin PEG connectors. Also, the HD 7850 won't draw more than 110W, unless you're going to overclock the card and run FurMark.

I would however recommend that you rather opt for a single higher spec'd graphics card than going for a dual graphics card setup!

The only reasons why I opted to go for 2x GTX460's long ago was:
1) 2x GTX460's was cheaper than 1x GTX480, and it outperformed it by a big margin in most cases + I already had 1x GTX460 to start with
2) I already had a high end system that supported SLI
3) Dual graphics cards look awesome

Dual graphics card setups would require that your motherboard support SLI/CrossFire.
You can also run into heat problems when the motherboard's 16x PCIe slots doesn't have other PCI/PCIe slots inbetween to leave a 1-2x slot gap between the graphics cards. For optimal cooling, you'll also require a large enough case to provide good airflow.
Your performance/watt is generally worse in a dual graphics card setup and you are likely to have issues in games that weren't developed to make use of dual graphics card setups. So you generally need a pretty big PSU for a dual GPU setup compared to a single GPU one.

So ja, those are just a couple of reasons why I'd advise to stick to a single GPU.

Ahh, thank you so much! I was wondering if my PSU had enough connectors and I couldn't find any info online and idk what to look for inside.

Thanks

I wanted the crossfire cause I have not done that before and 7850's are R1800-R2100 at the moment and mine was R2800 at launch so I figured it was a good option if you look at price/performance ratio.

My other issue is that a GPU better than my 7850 is so much more expensive, if I wanted a good enough upgrade I'd need a GTX 770+ or a 7970.
Cause I looked at the specs of the 760, R9 270x and 7950 and the improvement over a 7850 just isn't worth the price for me since then I can't buy a new CPU (I want i5)

I guess I'll just keep my 7850 until next gen comes out.

@ Pada
No the stock power draw on a 7850 is 130watts not 110. Even at 130watts there shouldn't be a heat problems, side panel fan is more than capable to removing trapped air, and it is winter.However the stuff that you mention is minor compared to the second slot only running at x4, considering he mentioned it was a regular board

Games are not directly coded for dual GPU's, that is what the DX API and display drivers are for to handle that.

Secondly I3 is hardly a bottle neck for 2 x 7850's the fact is, 7850 isn't even capable of running at a 3rd of the PCI-e bandwidth, no amd 7 series card is capable of using the full allocated bandwidth.In gaming at least, with mining there over all bandwidth bus usages is considerably better however it still doesn't make use of all allocated bandwidth.

Quad and tri sli have better results using bandwidth allocated.

Thanks for the info I was actually scratching my head wondering if my CPU is bottlenecking my GPU and I also couldn't find any answers on google.

All I ever got was general advice and not genuine comparisons.

What is your opinion on Crossfire 7850's vs waiting for the next GPU gen?



This is the PC box I want to purchase - so hoping that can crossfire, I also want a aftermarket CPU cooler (maybe) or water cooling (maybe) when I can afford it.

Don't know what else to ask...

 

[wizardofid]

There is no rush, ARMA III is so far the only game I have been unable to play at max settings.The problem is it's very likely that you are running the second slot at x4 speed, the impact isn't that major, but considering the bandwidth use of the bus, the performance is only about 10 to 15% slower on that slot, it is relative small, however that said, in single GPU mode the bus runs at full x 16, with dual GPU mode the speed drops to x8 on the first slot, that is because the slots both share the same bus, and bandwidth needs to be shared. This creates a fairly big problem on dual 7970 cards for example or two titans, these cards are a lot more capable of using more of the bandwidth the bus allows.

Which in return on a slower CPU creates a bottle neck, on both ends the CPU and the bus bandwidth.However don't be fooled, when some one mentions that the GPU memory runs at so many gazillion mega herts, this results in the bottle neck. GPU memory bandwidth is not linked to the bus bandwidth, it's the bandwidth between the GPU and GPU memory, people seem to confuse the 2.

Will a I3 bottleneck two 7850's not very likely, they simply don't use enough bandwidth, even at x4 and x8 bus speeds.

 

[EmileS]

Had 2x HD7850s on my PSU no probs. So, yours would handle it

 

[Rickster]

Had 2x HD7850s on my PSU no probs. So, yours would handle it

Isnt Crossfire unstable?

 

[EmileS]

Isnt Crossfire unstable?

Depends on what you do with it and what games you play. But, the drivers today are a lot better than it was 3 years ago, most of the kinks have been ironed out. I'd say it's 98% stable