would this be kinda pushing it?

[konakona]

I am in the process of helping my friend to build his new computer. It will most likely have the following:

HD4890 x2 in CF
3 7200RPM drives (1tb, 500gb, 500gb)
2 case fans, 1 fan on the cpu h/s, all downvolted for quietness
1 internal BD/dvd-writer
no other peripherals

The CPU could either be i7 920 or x3 720BE.

We are hoping to get some moderate to decent overclock both on the CPU and the GPUs.

extreme power supply calculator tells me he would need 535W of combined power, assuming he goes with i7 and clocks it at 4ghz (1.4v).

Now, I stumbled across a hot deal on a corsair PSU (620HX) at a great price of $70 shipped AR. Assuming he wouldn't be adding any more to the computer, would this PSU be enough? TIA!

 

[dualsmp]

It should work no problem although it's getting near the tail end of the rated power. The HX620 can take an overload of 746 watts so there is quite a safety margin:
http://www.hardwaresecrets.com/article/371/9

The 50% power level is generally where the PSU sweetspot is as far as efficiency. You could go for a 750w or 850w but also more expensive. If he games a lot I would go for a higher rated PSU, however if he is a casual gamer the HX620 should perfectly fine.

 

[alyarb]

assuming the i7 at 4 GHz needs at least 150w, plus 380w of the combined radeons, i would say closer to 560 to 575 total. you'll be fine. just consider this graphic.

http://dl.getdropbox.com/u/594924/i7_pwr.PNG

an additional 100 watts to get you from 3.8 to 4.0 ? If you don't want to max out your PSU, aim for 3.7 GHz, eh?

 

[geokilla]

That's too much for the Corsair HX620. Sure it can pull 791W from the wall, as Legit Reviews did when running 4870 X2 in CrossfireX, but it wasn't providing enough stable power for the GPUs.

 

[dualsmp]

Originally posted by: geokilla
That's too much for the Corsair HX620. Sure it can pull 791W from the wall, as Legit Reviews did when running 4870 X2 in CrossfireX, but it wasn't providing enough stable power for the GPUs.

If you check the overload test above it pulls 900 watts from the wall. The link you provided is somewhat vague. He blames the PSU but then never follows up whether a newer supply solved the problem. PSU's are rated DC power not AC power however Apoptosis goes on to state "791W on a 620W rated power supply... That's 171 Watts over the rating or 27.6% more!" He is comparing AC power to 620w DC rating. Anyways take it with a grain of salt.

 

[SparkyJJO]

I would imagine it should be fine.

You won't be at load all the time, so generally the system will be in the good spot for efficiency. When you are at full tilt, the PSU can do that too, that's what the 620W is for.

Buying a PSU that is 40% larger than needed for your max load is silly, because you won't be at your max load all the time and thus would only be using 20-30% of the PSU's power, outside its best efficiency range.

 

[Rubycon]

The fan will be LOUD at full load and internal temps very high. Rails will have most ripple and lowest voltages when the power is most needed. For that configuration 850 would be much safer and HX1000 would operate in the sweet spot for noise and efficiency.

 

[HOOfan 1]

Originally posted by: Rubycon
The fan will be LOUD at full load and internal temps very high. Rails will have most ripple and lowest voltages when the power is most needed. For that configuration 850 would be much safer and HX1000 would operate in the sweet spot for noise and efficiency.

I think a good 750W rated at 50C would be perfectly fine also. The HX620 would likely work....but yes, you would be pushing it. I don't really thing a 1000W woudl be necessary.

 

[SparkyJJO]

Originally posted by: Rubycon
The fan will be LOUD at full load and internal temps very high. Rails will have most ripple and lowest voltages when the power is most needed. For that configuration 850 would be much safer and HX1000 would operate in the sweet spot for noise and efficiency.

But it would only be under a full load when doing hefty gaming. At that point, you won't be listening to it. Didn't think the HX620 was capable of loud either but I've not had more than 300W load on mine.

I'm just curious why everyone is basing their noise and efficiency comments off of full system load instead of idle, where it would sit most of the time? As long as it can handle the system under full load within its 620W spec, there should be no problem?

Maybe I'm missing something.

 

[Lunyone]

Well I'm sure it'll handle both of the 4890's, but....ya know it will need 4 x 6 pin PCI-e power connectors, right??? The Corsiar 620hx only comes with 2 x 6+2pin PCI-e power connectors, so you'd have to get some y-cables to power up the other 4890 GPU, which I wouldn't recommend. I'd recommend getting the Corsair 750w tx model that comes with 4 x 6+2pin PCI-e power connectors and really is a better buy than the 620hx model. I know it doesn't have modular cables, but it is a better unit, IMHO. It also has 60A on the single 12v rail for the GPU's to use. The 620 hx has 50A on the combined 3 rails, which is plenty for what you need.
It's going for $120 - $10 MIR = $110 from Newegg. Amazon and Buy.com have it for $115 - $10 MIR = $105, so there are cheaper options too.
Newegg's link
CORSAIR CMPSU-750TX 750W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply - Retail

 

[konakona]

thanks for all the responses. I think he would be better off shelling out a bit more for a beefier model. We were going for a bigger one in fact, just that this deal was a bit hard to resist and had to do some quick fact check.

 

[Yellowbeard]

If you want modular, our HX series has a 750w and 850w due out any day now. If you do not need modular, the TX750 or TX850 are great choices for this rig.

 

[konakona]

yeah, I have a TX850 in my own system and it is super. I love the exterior design so much I wish I had a see-thru panel now

 

[geokilla]

Originally posted by: dualsmp

Originally posted by: geokilla
That's too much for the Corsair HX620. Sure it can pull 791W from the wall, as Legit Reviews did when running 4870 X2 in CrossfireX, but it wasn't providing enough stable power for the GPUs.

If you check the overload test above it pulls 900 watts from the wall. The link you provided is somewhat vague. He blames the PSU but then never follows up whether a newer supply solved the problem. PSU's are rated DC power not AC power however Apoptosis goes on to state "791W on a 620W rated power supply... That's 171 Watts over the rating or 27.6% more!" He is comparing AC power to 620w DC rating. Anyways take it with a grain of salt.

Switching to a 1000W PSU did fix the problem. I'd have to dig up the review on their site, but I think it was on the 4870X2 CrossfireX review.

If you don't need modular, I believe Newegg has some deals going on for Corsair TX PSUs.

 

[PUN]

620hx should be plenty for that rig.
two 4890 will draw just under 300w even at the highest peak load...not 380w.
I've pushed 3x4890 on my hx620 with i7 4.0ghz and similar hd setup.

 

[geokilla]

You know, all this time I misread the OP as 4890X2 in CrossfireX. Thing is, such a GPU doesn't even exist!

@OP. I take back my stand on that the HX620 won't be enough. It should be plentiful on your HX620.

 

[PUN]

Originally posted by: geokilla
You know, all this time I misread the OP as 4890X2 in CrossfireX. Thing is, such a GPU doesn't even exist!

@OP. I take back my stand on that the HX620 won't be enough. It should be plentiful on your HX620.

i also understood it as 4890x2 on CF, and soon realized 4890x2 doesn't exist