550W PSU enougth for crossfire?

[Stumps]

I'm looking to ditch the 2900XT I have in my rig for a Pair of Gigabyte Radeon 3870's, now that I have replaced my old GA-P35-DS3R with a GA-P35-DS3P (I got it real cheap at work).

Would my trusty Antec TPII 550W PSU be able to cope with a pair of 3870's?

It's specs are as follows

+12v1 - 19A
+12v2 - 19A
Max load 36A

+5v - 40a
+3.3v - 32a
Max load 530w (+5v, +12v, +3.3v)

the rest of my rig is in my sig.

 

[Avalon]

Should be fine. Each card only draws about 140W a pop, which is about half of your 2900XT. So even crossfired, you'd be getting the same power draw as your current rig.

 

[spittledip]

Seems like that will be pretty tight. you might want to get a 650 to 700 to be safe. What do others think?

 

[bryanW1995]

the 3870 only draws 1/2 the power of a 2900xt. if he's been using a 2900xt then he'll be fine with 2x 3870.

 

[nitromullet]

Originally posted by: bryanW1995
the 3870 only draws 1/2 the power of a 2900xt. if he's been using a 2900xt then he'll be fine with 2x 3870.

:thumbsup:

 

[Stumps]

Ok, thanks guys.

Next question, does anybody have an idea roughly how much power my rig is currently consuming, so I can work out how much head room I have left in the PSU?

 

[MarcVenice]

You've also got a waterpump hooked up to the PSU ? With a overclocked E4300, dual HD 3870's, I'd say it will be tight, and might run your PSU at 70-80% of it's limit or even higher during gaming ...

 

[Stumps]

Originally posted by: MarcVenice
You've also got a waterpump hooked up to the PSU ? With a overclocked E4300, dual HD 3870's, I'd say it will be tight, and might run your PSU at 70-80% of it's limit or even higher during gaming ...

Yeah I figured that I would be getting pretty close to the PSU's limits, I'll probably end up ditching the Watercooling kit for a decent HSF unit, when I go to rebuild the rig to add the new mobo and video cards....currently it looks like that I don't have enougth space in my case for the water pump and reservior once I add the second video card...

 

[RavenGuard]

You should def b fine. I'm looking into selling my HD2900XT... If I could get $150 it's worth the extra bit to save the power consumption/heat/noise/extra features of the new card.

I run a 640 watt and I feel I still have quite a bit of headroom.

Just make sure your supply is good quality, it's usually more important than raw wattage. If you're unsure, keep a "new powersupply" savings jar in case of emergencies, and blow it on your next pc anyways

 

[Stumps]

I'll probably end up getting a 850w or bigger in the near future, but I want to get things set up before christmas.

 

[ROEHUNTER]

Originally posted by: RavenGuard
You should def b fine. I'm looking into selling my HD2900XT... If I could get $150 it's worth the extra bit to save the power consumption/heat/noise/extra features of the new card.

LOL That is exactly what I sold my 2900xt for.

 

[error8]

Use this for calculating power consumption http://www.extreme.outervision.../psucalculatorlite.jsp

 

[Stumps]

Originally posted by: error8
Use this for calculating power consumption http://www.extreme.outervision.../psucalculatorlite.jsp

hey, nice.

According that that PSU calculator, at 100% load (unrealistic usage) my system is using 510W and at the recommended 90% load it is using only 456W, so I gather that using a pair of 3870's should be ok with my current PSU.

 

[MarcVenice]

456w on a 550w unit ? Even if the unit is rated at 50c continous, 450w is quite a lot to ask from it, if it runs hotter then 50c, then you'll lose 3-4w of capacity for each degree celsius it goes up ...

Keep that in mind, and a hot PSU degrades faster then a cool one. It might run, but like I say way to often, for how long ? If you are spending upwards of 1000$ on a PC, don't skimp on the PSU, that's what it comes down too. I know you've got the PSU allready, but the same still apply's, although it was unforeseen ...

 

[bryanW1995]

throw this question into the psu forum. there are some very knowledgeable guys over there.

 

[Stumps]

Originally posted by: MarcVenice
456w on a 550w unit ? Even if the unit is rated at 50c continous, 450w is quite a lot to ask from it, if it runs hotter then 50c, then you'll lose 3-4w of capacity for each degree celsius it goes up ...

Keep that in mind, and a hot PSU degrades faster then a cool one. It might run, but like I say way to often, for how long ? If you are spending upwards of 1000$ on a PC, don't skimp on the PSU, that's what it comes down too. I know you've got the PSU allready, but the same still apply's, although it was unforeseen ...

If the 456w is correct, my PC has been running like this since june and hasn't missed a beat, barely any hot air is blown out the back of the PSU and it is only slightly warm to touch...

But you are right, I don't intend to keep using the 550 watter for to much longer, I'm just hoping that it will last a couple months in a crossfire setup until my funds recover to purchase a beefier PSU.

 

[MarcVenice]

Wait, with your current setup, your rig will most likely not use more then 300-350w under load. I thought the 456w was with the crossfired 3870's ...

 

[Stumps]

Originally posted by: MarcVenice
Wait, with your current setup, your rig will most likely not use more then 300-350w under load. I thought the 456w was with the crossfired 3870's ...

no, that 456w was what I got when I entered in my current specs (it didn't have the 3870 in it's video card list)....I think that this figure is a worst case scenerio for a PSU as it is a 90% load rating...but I could be wrong.

 

[MarcVenice]

Yeah, and the PSU calculator is designed to give the amount of wattage you have to buy, to be safe. It means you have to buy a qaulity 456w PSU, not that you are using 456w. Look up the latest batch of reviews from anandtech and other websites regarding the 8800gt and the HD3870, they will show total pwer consumption being around 200-250w or so. Hell, power readouts regarding a 8800gtx and a q6600 have showed to be around 250-300w. You still think your rig is using 456w of power ? Get real hehe, besides, if it would be, your PSU would be running pretty hot

 

[Stumps]

Originally posted by: MarcVenice
Yeah, and the PSU calculator is designed to give the amount of wattage you have to buy, to be safe. It means you have to buy a qaulity 456w PSU, not that you are using 456w. Look up the latest batch of reviews from anandtech and other websites regarding the 8800gt and the HD3870, they will show total pwer consumption being around 200-250w or so. Hell, power readouts regarding a 8800gtx and a q6600 have showed to be around 250-300w. You still think your rig is using 456w of power ? Get real hehe, besides, if it would be, your PSU would be running pretty hot

that's what I would have thought...but it's barely warm at all...so I guess it's safe to say that I should be fine then with the 550w Antec.

 

[MarcVenice]

That's not what I'm saying, I think you will be in fact NEAR the psu's maximum capacity if you throw two HD 3870's in there ... Your power usage might go up to 400w or so ...

 

[Stumps]

Originally posted by: MarcVenice
That's not what I'm saying, I think you will be in fact NEAR the psu's maximum capacity if you throw two HD 3870's in there ... Your power usage might go up to 400w or so ...

ahhh, now I get you...but even at 400w's would it stress the PSU to the point of failure?

 

[MarcVenice]

Originally posted by: MarcVenice
Keep that in mind, and a hot PSU degrades faster then a cool one. It might run, but like I say way to often, for how long ?

 

[Stumps]

I guess I just have to see what happens and keep an eye on the PSU...but I will definately be getting a 850w or better very shortly....hmmm I wonder if I can "borrow" one from work

 

[MarcVenice]

An example, I might be off a little here, but let's say a HD3870 will consume the same as a 8800gts 640mb. This is what jonnyguru said about running those in sli in the following PC: 680i board w/ QX6800, 2x1GB PC2 8500, two Seagate SATA drives in RAID0, one optical, one floppy, three fans run at full RPM, no PCI-e cards, on board sound, NIC, etc. USB KBD and mouse. Room temperature is just around 23.5C.

8800 GTS 640MB x 2 SLI bridge on build 1
Total: 484W DC.
Total +12V2: 8A
Total +12V1: 24.6A

Comments:

Not much different going on here still. The current going through the 8-pin (which may be supplying current to the CPU, but also to other parts of the board) went down a little, but the rest of the +12V consumption went up a little. A single +12V rail 500W and up (like the Corsair HX520W or Ultra X-Pro/X3 600W) or 600W and up with four +12V rails or more (like the SilverStone Strider ST60F) would be a good candidate here.