Topic: 7950 + 6850 + 600W PSU is it enough? (Read 2331 times)

I'd go for the corsair.  The 1050 will comfortably accommodate 4 GPUs if you undervolt them.

Good point ssateneth.

I use my machine for a lot of things, mining is one of them. Whilst i'm not at the PC i put the intensity to max.

My main reason for taking out the 6850 is I only get 200-218KHs out of it and when mining with the pair both monitors stopped displaying. I jumped to the conclusion this was related to power and after a few minutes i turned off the PC removed the card.

I'm tempted to get another 7950 but will wait till the 9 series comes out as it should either price drop the 7950 or the new ones will be worth buying.

In theory i can probably run both cards ok but i didn't think it's worth the risk.


RChevalier point about the PSU is a good one and makes me think about getting a better rated PSU as mine is only a bronze.
My old PSU will be used for a mining rig with the 5850 and the 6850 in it.

Looked at Gold and above for PSU.

Which of these would you recommend?

1000W
http://www.ebuyer.com/265710-ocz-zx-series-1000w-80-gold-psu-fully-modular-single-12v-rail-ocz-zx1000w-un
http://www.ebuyer.com/392055-corsair-hx-80plus-gold-certified-modular-power-supply-1050w-cp-9020033-uk

850W
http://www.ebuyer.com/279546-corsair-txm-850w-modular-psu-cp-9020004-uk
http://www.ebuyer.com/257234-corsair-tx-850w-v2-psu-80plus-bronze-certified-cmpsu-850txv2uk

How are you getting the limit? If it shows 600 watts at the wall, you are not at the PSU's limit. Power supplies are rated by how much DC power they can put out, not by how much AC power they can pull from the wall. This is where inefficiencies come in. If your 80% efficient power supply is pulling 600 watts at the wall, its only doing 480 watts DC. When your power supply is pulling 750W at the wall, then it's at the limit since it'll be doing 600 watts DC

Also, if you can front the cost, try to go for a higher rated PSU.  Some actual numbers from my personal rigs for your reference:


Rig1:

Silverstone Strider 1000W Silver Plus - $190
draws 960W (Kill-a-watt)


Rig2:

Seasonic X-1050W Gold Plus - $230
draws 880W (Kill-a-watt)


So the upfront cost difference is $40.  The amount I save on 80W difference over 24/7 year round is $84 for me with my $0.12 per kW/H.  If you live in an area with higher power cost, this will mean a lot more.

850W is not that much more interms of cost, and if you ever decide to add a third 7950, then you are already setup to handle all 3 GPUs.

Hi all

plugged in my 7950 and my 6850 and it worked. I was measuring wattage from the PSU and mining with both put it very close to the limit.
I could turn down the intensity but in the end i took out the 6850 as it's only getting 218KHs at I17 and overclocked as much as possible.

Might get a new PSU and another 7950 then setup a separate rig with some old components and the 6850 and 5850 with my current PSU.


What would people recommend for a PSU for 2 7950?
750W or 850W

I was looking an an XFX 850W PSU but wanted to know if they are any good. Looks like they are made by seasonic like Corsair ones are.

Any recommendations?

It's very possible.  I have one rig with a 6870 and a 7950 on an Antec 550W platinum.  Both cards are undervolted to 1087.  According to my Kill-a-watt, the 6870 draws 133W and the 7950 draws 212W.

The best thing to do is get a killawatt http://www.p3international.com/products/p4400.html and check how much your idle system uses. Then lookup the maximum amperage used by your cards and get something good enough. I try to stay above the maximum so theres some room.

I used to run dual 6850s and a 5850 on a 630 watt raidmax. It worked as long as I didn't overclock anything and undervolted everything. However, overclocking anything would draw too much and the PSU would shut down. If you are using a lower power CPU (under 100 watts) you could get away with it as long as you don't overclock anything too far. (Back off if you have instability issues of any sort. If the PSU dies, RMA it, and don't getv as greedy next time.)

Thanks everyone. Some very mixed views on here.
According to eXtreme PSU Calculator my setup will only use 451W at full load (Assumes no overclocking)
I'm not convinced by this.

The 600W power supply will at least take the 7950 on it's own.

I'm tempted to put the 6850 in but not mine on it for now. what do people think?

I would like to get another 7950 at some point and would need a new PSU anyway, what would you all recommend for the PSU?

Working backwards forwards. Usually to much power will cause things to screw up.  You will see shit like your ram not functioning.  Fans slowing down.  Hardware heating up,  Strange Sounds from the PSU. Over time the PSU if built properly will just die without hurting any hardware. Poorly built PSUs will explode.  But mostly the caps swell and shit burns up on the psus pcb.

I decided to build a rig for catching up on a few years of gameing and some alt coin mineing.  I have some of the samw le specs as you minus the dvd rom..

As said in the post above you CAN do it.  But myself I like to allow for a buffer.  As said a breakdown of hardware will help

I'm going to disagree with you here. I believe you can power a 7950 and a measly 6850 off of your 600 watt PSU. There is not a snowballs chance in hell that a 6850 uses 250 watts. You need to get your kill-a-watt figures right. Get in a proper baseline load with no GPU and baseline 100% cpu load with no GPU before you start throwing GPUs into the mix and deciding what uses what amount of power.

IMO, I don't believe a setup as yours uses much more than 60 watts while idling (An MSI Z77A-G45 motherboard with dual core sandy bridge celeron, 2x2GB RAM, hard drive, keyboard, and mouse used 25 watts at the wall for me for comparison while idling). A fully loaded 2600K worst case scenario is an additional 140 watts on top of that using linpack which is designed to max out CPU power in any way shape or form; typical max loads probably won't see more than an additional 100 watts on the CPU though so we'll say 100 watts, so assume 160 watts fully loaded baseline.

An idling 7950 will use about 20 watts (or 1 watt if it is an unused secondary card due to zero power technology). An idling 6850 will likely use about 10 watts. Fully loaded 7950 (200W TBP) with +20% powertune is 240-250 watts, and a fully loaded 6850 (127W TDP) with 20% powertune is ~150 watts. Adding up all those figures, we get 560 watts, or if you happen to be running linpack as well, we get the magical 600 watts.

properly undervolted, a 7950 at 600k/h eats just north of 200watts

is this for scrypt or bitcoins? if for scrypt you can pull it off just disconnect the extra hd and other unnecessary things. for scryt you underclock the card and a 7950 will be somewhere around 250?

Thank you,

Looks like i need a new power supply then.
What would you recommend?
I may put another 7950's in later on so with that in mind i may as well get a PSU which can handle both.

What's the easiest way to monitor how much power you are drawing?

600 watt isn't going to cut it...
You would push close to 600 watt for the whole system with just the 7950 overclocked (almost 400 watt [369 watt battlefield load tested] use for the card itself) pushing full load, a non overclocked version will push 250 watt [235 watt battlefield load tested] system draw as well.  Add in the 6850 at around 250 watt (229 watt 3dmark06 tested) and you're asking for disaster.

Power is very important and it can behave is unexpected ways meaning a simple shut down because too much load to the extremes of blowing multiple parts in your system and at the far end of the spectrum and rare but possible causing a fire.

Hi there

I'm currently running a 6850 and a 5850 on a 600W Corsair PSU in:

Corsair 600W CX Builder Series 80 Plus PSU
Core i7 2600k
Corsair Vengeance 8GB (2x4GB) DDR3 1600Mhz
Gigabyte GA-Z68X-UD3-B3 Z68 Socket 1155
Arctic Cooling Freezer 7 Pro rev 2 Socket 1155
1 SSD
1 HD (7200)
3 120 MM fans
1 140 MM Fan
1 DVD RW

Will i be ok to replace my 5850 with a 7950 and keep using the same PSU or am i going to have issues?

Also what happens if you draw too much power from your PSU does it shut down or blow?