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4870x2 amp requirements

E

edifyingkarma

[H]ard|Gawd
Joined
Mar 8, 2008
Messages
1,464
Hi all,

I recently purchased a 4870x2 ($195) with the hopes that my 750watt 4 rail 12v+ 18A per rail (dell make) would be just sufficient enough to run well. However, while playing various games with settings cranked up, I have experienced several power downs which has lead me to believe that my power supply is not providing suffiecient amp room.

Is there any way around this aside from underclocking or should i just suck it up and buy a PSU. If a PSU is suggested, keep in mind that I intend to build a new system in about 1-1.5 years and would like to use my PSU in that system (hopefully something quite beefy). My thoughts are to buy a substantially high watt rated PSU for future reference but I am worried that my efficiency will drop badly causing extra high electric bills if I am not drawing near spec wattage. Should I worry about this? I am currently running a Q6600 @ 3.3, 4 HDDs, some led lighting, and a few extra fans. Newegg has Corsair TX 950w on sale right now and I am considering this PSU to future proof.

Thoughts and opinions are appreciated.
 
I'm running my hd4870x2 ocd with rest of rig ocd as well with a 620 with no issue. Dell 750 should suffice, odd. Unless you're gonna quad sli the 950 is a bit much. 750 is more then enough. Oh and about issue: the rated voltage is how much it can put if needed. It won't actually use that much, the amount of electricy used won't change until you change parts.
 
unrealsword said:
I'm running my hd4870x2 ocd with rest of rig ocd as well with a 620 with no issue. Dell 750 should suffice, odd. Unless you're gonna quad sli the 950 is a bit much. 750 is more then enough. Oh and about issue: the rated voltage is how much it can put if needed. It won't actually use that much, the amount of electricy used won't change until you change parts.
Click to expand...

The problem I am encountering is amp overload on the 12v rails. Sure 750 watts is enough total power wise but the 12v is broken into 4 rails thus failing to provide enough amp room. My computer keeps powering down under heavy load which indicates a PSU failure from all that I've read.
 
you have alot of hard drives...and they all use amps off the 12volt rails too. You know how many amps you have 72.

heres a list of all graphics cards and amps...except for some reason yours is the only one thats blank..lol
So im sorry i cant help more, but two 5870's only use 55-60 amps...u gotta be lower than that.

http://forum.msi.com.tw/index.php?topic=104805.msg812417
 
My total system amps is 72 but only 2 18A rails are supplying power to my videocard. That comes out to a total of 36 amps to the video card. Seeing as the the 4870 calls for a min of 32 amps, don't you think that 36 amp would be a bit too low for a 4870x2? If it truly is sufficient than why would I have powerdowns during heavy load scenarios?
 
yes of course its too low...look at the 55-60 for two 5850's and i suspect your just under that or maybe equal since they tried to lower power for the new cards.
I just saw all the overclocking and extra fans u have all use amps on 12v rails too, led's probably nothin at all.....but the video card will need more than 36amps. probably 50 amps at least.
You can solve all your problems by getting a psu with a single 12volt rail...my 750watt only has like 60amps on a single rail and it was supposed to be the best when i got it.
 
edifyingkarma said:
My total system amps is 72 but only 2 18A rails are supplying power to my videocard. That comes out to a total of 36 amps to the video card. Seeing as the the 4870 calls for a min of 32 amps, don't you think that 36 amp would be a bit too low for a 4870x2? If it truly is sufficient than why would I have powerdowns during heavy load scenarios?
Click to expand...

Its less then that. I forget how you run the numbers exactly but you dont just add up amps across different rails like that. Your videocard is only probably seeing about 30amps or so which is a problem since 4870x2s are loud hot power hungry beasts.
 
Unless the PSU is defective, I don't think it's a lack of amps or wattage that's the problem. I also have a 4870 X2 using a 700 watt PSU with four 18 amp rails.

I think when you see amp requirements listed for a graphics card, that requirement isn't what the video card is drawing, but their rough estimate of how many amps your PSU needs to run the entire computer with the video card.

Along with my 700 watt PSU and 4870 X2, I have the quad core CPU, had up to 6 hard drives at once, along with a water pump and half a dozen 120mm fans. It all kept running while gaming somehow. :)
 
DeadSkull said:
Its less then that. I forget how you run the numbers exactly but you dont just add up amps across different rails like that. Your videocard is only probably seeing about 30amps or so which is a problem since 4870x2s are loud hot power hungry beasts.
Click to expand...

Alright, so now that I know for sure, would i experience degrading power efficiency if I go ahead and purchase the TX 950w in anticipation that I will one day use its capacity even if I am not currently using that much juice. Will it raise my electric bills substantially?

On side note, it seems I have received a bit of a gem as far as this 4870x2 is concerned. With fan @ 42% (doesnt sound bad) I idle at about 40-42c and under load I am only hitting around 75-80c
 
well u seem like an intelligent person and you pretty much diagnosed your own problem...so i don't want to insult you. I do remember reading and i've heard people combining the (say 4) rails in your case into one powerful 12v rail to get more amps to power hungry video cards...did u try this? I don't even know if all psu's do that, just trying to help u save a few bucks if possible. If not..you know how many amps your gonna need for a new one. Goodluck
 
No matter how many watts a psu is rated for say 1000watts....it only puts out what your using..say 600watts. so you would never pay more on your bill unless you are actually using more power. I think its not a great idea to max out a psu on amps and watts...the life span would be pretty short and you know your gonna need the juice when you upgrade your card again so just buy with the future in mind. My theory is it's better to pay a few extra bucks on the psu and not have problems down the road.
 
Okay all, Ironically, when I decided to break down and post here for advice, I found my answers elsewhere.

This is what I was refering to efficiency wise http://www.anandtech.com/casecoolingpsus/showdoc.aspx?i=3413&p=3

With all this said and done, ive decided to go ahead and purchase the 950w to future proof as I am still with in range of power usage to not be affected by the efficiency curve.

Thanks for stopping by to offer your insight.
 
l3uLLDoZeR said:
you have alot of hard drives...and they all use amps off the 12volt rails too. You know how many amps you have 72.

heres a list of all graphics cards and amps...except for some reason yours is the only one thats blank..lol
So im sorry i cant help more, but two 5870's only use 55-60 amps...u gotta be lower than that.

http://forum.msi.com.tw/index.php?topic=104805.msg812417
Click to expand...

Is that link accurate? 40A for the 5700s and 35-40A 5670?! I've seen the same in a guru3D review of those cards but I thought they were severely overestimating.

Here's my logic:
The 5xxx series is more power efficient as shown in their TDPs (5770 108W vs 4870 150W).
Watts = Amps x Volts

Thus Amps = Watts / Volts
5770:
9A = 108W / 12V
http://www.guru3d.com/article/radeon-hd-5770-review-test/11

4870:
12.5A = 150W / 12V
http://www.guru3d.com/article/amd-ati-radeon-hd-4870-1024mb-review/4
What's odd is they say cross fire is another 150W (which makes sense since the TDP is 150w) and another 8A when my calc shows 12.5.

Of course I'm only looking at the video card's load. But assuming you try each card under the same system setup, the rest of the system power draw will remain the same of course. So how can they say such higher amperage required on the 5xxx series?

Here's a link to show you your Amperage on your 12V rails.
http://www.xtremesystems.org/forums/showthread.php?t=228553

Edit: Also a relevant read:
http://www.tomshardware.co.uk/geforce-radeon-power,review-31495-6.html
 
Last edited:
Xzyrus said:
Is that link accurate? 40A for the 5700s and 35-40A 5670?! I've seen the same in a guru3D review of those cards but I thought they were severely overestimating.

Here's my logic:
The 5xxx series is more power efficient as shown in their TDPs (5770 108W vs 4870 150W).
Watts = Amps x Volts

Thus Amps = Watts / Volts
5770:
9A = 108W / 12V
http://www.guru3d.com/article/radeon-hd-5770-review-test/11

4870:
12.5A = 150W / 12V
http://www.guru3d.com/article/amd-ati-radeon-hd-4870-1024mb-review/4
What's odd is they say cross fire is another 150W (which makes sense since the TDP is 150w) and another 8A when my calc shows 12.5.
Click to expand...

Your figuring is correct. Anyone that thinks a video card (any video card) uses 35A on a 12v rail (420W) is fucked. Also check the [H] full system power consumption notes in their video card tests for a much better idea of how much power these cards consume.

I think what people tend to not distinguish is between what the entire system will use off the 12v rail, and what just a video card will need off the 12v rail. When you seen Nvidia, ATi, etc. say that they recommend a power supply with a 35A or 40A 12v rail, they're referring to your whole system, not just the video card. I can't believe how many people still don't understand this. They make overly-conservative ratings so that no matter what kind of hard drive, CPU, and fan configuration you have in your system, you'll still have more than enough power for a video card.

Any quality 750W power supply will run an HD 4870 X2. Two of OP's 18A 12v rails are more than sufficient for that card. Way more than sufficient; as stated, it won't suck anywhere near the 432W of two of those rails combined. This would probably tell us that the power supply just isn't up to delivering its rated capacity, or there's a problem somewhere else in the system. Glenn37216 is correct - 270W at full load (Furmark or the like) is much closer to reality.
 
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