Is 600w enough for 7870ghz xfire?

[codyray10]

I recently purchased a second 7870ghz edition to pair with my current one for some crossfire goodness. However, one thing I didnt think of at the time of purchase was if my current power supply will have enough juice to run the rig without issue. AMDs website says a minimum of 600w psu is recommended for 7870 xfire.

This is my psu http://www.microcenter.com/product/301547/ModXStream_Pro_600W_Modular_ATX_Power_Supply


It powers..
AMD FX6300 4.4ghz @ 1.425v (95w stock, not sure what it draws with the OC)
7870ghz edition 1100/1300 stock volts
3 case fans (antec 900)
2 SSDs
1- WD 500gb black hdd

 

[hack_tc]

It will probably work fine. I run a 7850 OC xfire setup, 3570k i5 @4.5ghz, with 1 hdd/1ssd, and several fans, on a 550w PSU (80+ gold rated), and haven't had any issues.

I think yours is 80+ silver, so its not some piece of junk PSU like most that are out there; and companies tend to exaggerate power requirements to be on the safe side.

 

[lehtv]

I wouldn't trust that unit with 7870 crossfire and an overclocked FX-6300. It doesn't have the required four PCIe connectors, and it's not good enough quality that you could safely use molex to PCIe adapters, given that it is a multi rail unit. (Putting graphics card type load on a rail designed to power things like fans via peripheral connectors may overload the rail.) How old is the PSU, by the way?

I'm wondering why you want to crossfire that card? For one thing, your CPU needs upgrading before it can take full advantage of a graphics card upgrade on 1080p resolution, and secondly, I think it'd be a better idea to sell the 7870 and upgrade to a 280X. That would not be as great an upgrade in terms of pure framerates, but you would avoid any and all hassles resulting from running two cards: noise, heat, power consumption, lack of connectors, microstutter, lack of Crossfire profile, inconsistent performance compared to a single card.

Another issue that I see is that your motherboard doesn't support PCIe x8/x8. It has two PCIe 2.0 x16 slots, but the second one is electrically limited to x4 bandwidth which limits the performance of a graphics card installed in that slot.

So given the fair chance of CPU bottlenecking and the lack of proper Crossfire support on the PSU and motherboard fronts (not to mention the disadvantages of Crossfire itself), I don't really see any other option than to return the 7870. If you want to upgrade, a 280X would be a decent option although it may also be bottlenecked by the CPU in some games. The best option, if you can afford it, would be to upgrade to Intel Haswell i5 and a 280X or even a 290.

I think yours is 80+ silver, so its not some piece of junk PSU like most that are out there; and companies tend to exaggerate power requirements to be on the safe side.

Efficiency doesn't really say anything about reliability, although efficiency and reliability may have some correlation. Also the ModXStream 600W is 80+, not even Bronze rated. Says so right there on the Microcenter page the OP linked.

The unit is by no means high quality. It is alright, but not alright enough to use molex to PCIe adapters. Despite the 600W label, the +12V output is actually only rated for 504W, and it can just barely output its rated wattage, which means it is definitely not designed for continuous 600W output.

 

[codyray10]

How old is the PSU, by the way?

I believe I've had it just over a year

I'm wondering why you want to crossfire that card?

No reason in particular honestly. I have one that's a pretty good clocker and came across a good deal on the FS/T forums here for the same model at a good price. I like to tinker, and I'm interested in seeing how the xfire performance would be. Also, with BF4 around the corner I figured the extra performance wouldn't hurt.

Another issue that I see is that your motherboard doesn't support PCIe x8/x8. It has two PCIe 2.0 x16 slots, but the second one is electrically limited to x4 bandwidth which limits the performance of a graphics card installed in that slot.

This was something I was aware of prior to making the purchase. I did some reading, and while there is definitely a perfomance hit, it didn't sound like it would be that substantial.

 

[lehtv]

Okay. Well if you must get to play with Crossfire despite the x16/x4 motherboard and the CPU that will almost certainly bottleneck the cards in BF4, upgrade your power supply first and keep the ModXStream as a spare in case you ever need to troubleshoot. Seasonic G650 $80 AR

EDIT: I still think though that the second 7870 is a lost cause. For BF4 you'll want a fast CPU first. http://www.hardwarepal.com/battlefield-4-cpu-gpu-benchmarks/8/

 

[codyray10]

Okay. Well if you must get to play with Crossfire despite the x16/x4 motherboard and the CPU that will almost certainly bottleneck the cards in BF4, upgrade your power supply first and keep the ModXStream as a spare in case you ever need to troubleshoot. Seasonic G650 $80 AR

EDIT: I still think though that the second 7870 is a lost cause. For BF4 you'll want a fast CPU first. http://www.hardwarepal.com/battlefield-4-cpu-gpu-benchmarks/8/

I appreciate the input. I may end up selling the two 7870's and upgrade to something else, who knows.

 

[hack_tc]

Thanks, lehtv, for catching my mistake. I had looked up that PSU on Newegg, and saw the small white 80+ logo, along with a high price and assumed silver rating. I didn't even know they classified 80+ certified without even a gold/silver/bronze tagged with it.

Anyways, good luck codyray10. Hope everything turns out well for you. Right now, especially with the low prices of 7950s, your likely going to have a hard time trying to sell a 7870.

 

[lehtv]

Actually, ebay shows plenty of sold listing s for 7870s, the avg sale price is about $120-130

 

[codyray10]

Actually, ebay shows plenty of sold listing s for 7870s, the avg sale price is about $120-130

That's not too bad, it's almost what I paid for one.

I grabbed a new power supply today that should be plenty sufficient to run everything. Will get it all installed tonight and see what kind of performance gains I'm able to get running crossfire with x16/x4 configuration. That'll help me determine whether I keep them or sell them. I've found a handful of benchmarks that show there's anywhere from a 1-20% performance loss, depending on the game. Luckily the games that show the biggest loss, I do not play.

 

[lehtv]

What power supply did you get?

 

[codyray10]

Due to my limited budget at the moment, I risked trying out a EVGA unit. I've heard some good and bad about EVGA as a company but I have zero experience with them so I figured why not give it a try. It was either this one or a cheaper no name brand.

http://www.microcenter.com/product/404598/SuperNOVA_NEX750B_750_Watt_ATX_12V_Power_Supply


EDIT: I think the microcenter specs are wrong. It has 4 12v rails, the microcenter link says just 1. http://www.newegg.com/Product/Product.aspx?Item=N82E16817438007

 

[lehtv]

EVGA is alright as a brand, but their PSUs are made by FSP. FSP is okay, not the best but not far from unreliable, so I think you made a good choice. But it wasn't the best you could've done either... $80 isn't THAT limited, and since you don't need 750W, you could've got a better quality 650W unit instead: XFX 650W $80 ($70 AR), manufactured by Seasonic (quite a bit better than FSP), or just $10 more for a Seasonic G650 which is one of the best quality units ever to hit the market.

 

[spat55]

My 550w XFX hasn't been able to do HD 7850 crossfire, it starts ticking with the second card connected now, so looks like I need at least a 800w.

 

[lehtv]

How do you get from "550W is not enough" to "need at least 800W", when one card consumes 110W at stock?

In terms of power capacity, 550W definitely IS enough for 7850 crossfire though. 7850 crossfire only uses about 350W for the whole system when gaming, and that unit should handle its full 550W rating load continuously, both according to XFX's claims and reviews.

I have no idea why the unit starts ticking at that load... maybe it's time to RMA it and see if the replacements works better?