PSU for 7870 ghz+overclocking

[crazymonkeyzero]

Hi Guys,

Was going to buy~$200 gpu, was thinking either the 7870 ghz which is currently going for sale for around $190 AR or the 7850 2gb. The question I had is whether or not my PSU will be enough for the 7870ghz. I have a corsair CX500M. Also if I did go with either card would I have headroom to moderately overclock the cpu, to say~4.5ghz?

Here is my system (minus the video card of course)

Intel Core i5 2500k (currently at stock)
Corsair 500w psu (80+ bronze)
2x4gb ddr3 1333 crucial memory (1.5v)
single 7200rpm 1TB hdd
single dvd rw drive
Four 120mm fans.


Thanks for any advice on the matter

 

[Soulkeeper]

If you pushed all those components to the max you could hit the limit of that psu.
But for moderate/mild overclocks you're likely not going to have a problem

Just for reference:

7870 and 7850 in my system in my sig
i'm pulling about 370W from the wall with gpus/cpu loaded right now
platinum 860w psu here
with my 400W gold this same config would trigger the ocp every now and awhile when launching a game or a browser video kicking in. (became stable when underclocking the cpu a bit).
Note that this is with TWO video cards.

Maybe someone else can fill on exactly how much juice your cpu would pull with a 4.5GHz oc, but I think you'd likely be ok.

 

[crazymonkeyzero]

Thanks for your response Soulkeeper.

I think I'll just buy a 600w psu to keep a peace of mind, and put my 500w into another rig. That way I'll have enough headroom for that 7870 as well as be able to OC without power restraints.

 

[Torn Mind]

It's plenty. The 12V rail should be able to handle 456 watts, and the draw will certainly be less than that.

 

[IGemini]

My system pulls about 350W from the wall while under highest load (which has been playing Skyrim thus far). Pretty sure I'm using a bit more power than yours, and even using your unit it would only hit 70% load. I think you'll be fine.

 

[gammaray]

a 7850 card draws maximum 100W, and a 7870 115W. So 500W is plenty.

http://www.techpowerup.com/reviews/Club_3D/HD_7850_RoyalQueen/26.html

 

[Soulkeeper]

a 7850 card draws maximum 100W, and a 7870 115W. So 500W is plenty.

http://www.techpowerup.com/reviews/Club_3D/HD_7850_RoyalQueen/26.html

Typical usage you're correct, but peaks are closer to 165 (stock) and they can vary 20w or more between manufacturers. For the 7870 add an extra 20W, GHz edition a few more watts, then overclock and you're up to 200+

 

[kalrith]

I have a 2500k at 4.1 GHz and a 7870 at 1100 MHz. I think my max load is ~330W at the wall, but I can confirm tonight if you want. I have the Antec Neo 620W psu, which should be enough for 2 7870s.

As long as that's a decent 500W psu, then you should be fine.

 

[crazymonkeyzero]

Thanks for the info everyone. I know the 500w will be enough for the 7870, but I hear that leaving the psu under heavy load all the time (70%+) can gretly shorten lifespan, so I guess having a little head room wouldn't hurt.

 

[kalrith]

Thanks for the info everyone. I know the 500w will be enough for the 7870, but I hear that leaving the psu under heavy load all the time (70%+) can gretly shorten lifespan, so I guess having a little head room wouldn't hurt.

Well, assuming you pull 330W at full load at the wall at 80% efficiency, you'd only be using 264W of your 500W power supply.

Even if your psu is 90% efficient, you'd have to pull 389W from the wall to be at 70%, and you'd probably need 2 7870s to do that. At 80% efficiency, you'd have to pull 438W from the wall to be at 70% of 500W.

 

[lehtv]

What do the from-the-wall estimates and efficiencies have to do with anything?

70% of 500W = 350W.

A system with an overclocked 7870, an overclocked i7-965 (whose idle wattage is much higher than that of a 2500K), and extras like water cooling and cold cathodes, consumes a bit over 300W from the wall with the GPU at full load (peak wattage, not average gaming wattage). This is measured from the wall using a 1200 watt power supply, so expect bad efficiency at this load. The DC wattage is somewhere around 250W or 50% of 500W. Obviously the OP need not be concerned about running the PSU at over 70% for extended periods of time, or even for short periods.

 

[kalrith]

What do the from-the-wall estimates and efficiencies have to do with anything?

They have to do with the OP wanting to stay at less than 70% load on his psu. Since his psu provides 500W of DC (not AC), I assumed he wanted to stay at 350W DC or less. Since several of us are providing numbers taken at the wall, that makes efficiencies are very relevant.

If my very similar system pulls 330W from that wall (AC) and runs at 80% efficiency, then it's only using 264W of DC, which is about 50% of his psu's capacity.

Put another way, a 500W psu providing its full load (500W DC) at 80% efficiency will be pulling 625W from the wall. 70% of 625W = 437.5W AC.

 

[lehtv]

The from-the-wall numbers we're providing are not obtained using the OP's PSU

 

[kalrith]

The from-the-wall numbers we're providing are not obtained using the OP's PSU

Really? I had no idea. I thought everyone in this thread had the same psu

He's asking if his psu that generates 500W of DC will be sufficient for this system. He also stated that he wants to stay below 70% of his psu's wattage. By only providing from-the-wall numbers and not talking about efficiency, he might think that pulling 350W from the wall is using his psu at 70% of its capacity. That's only the case if one has a 100% efficient psu.

My posts are meant to steer him away from that and realize that 350W of DC will be pulling much more from the wall. So, he doesn't need to be too concerned if someone with a similar system says they're pulling 330W from the wall, because it's much less than that in DC.

In other words, a decent 500W psu is definitely sufficient for the OP's system and will likely be using less than 55% of its max wattage at full load.

Edit: Changed wording to try to sound more sarcastic than mean

 

[lehtv]

Oh, I didn't realize you were trying to explain to him that PSUs are not 100% efficient. I assumed he knew that already

 

[Wuzup101]

As most posters above said, you will be fine. For reference, my gaming / main system in my signature pulls 650w from the wall while running prime and furmark at the same time. It pulls significantly less doing any real world activity (unless you actively play skyrim, BF3, and encode video at the same time). IIRC, it pulls no more than 250 from the wall just running prime 95. The GPUs account for 200-220w each (from the wall)... and both pull more power than the cards that you are looking at.