Zalman 850W not cut it for GTX 275

[Narynan]

So, I have been looking into getting a Nvidia 275. However, one of the things I am looking at has been the power reqs for this card. It looks like I need 40A for this card. I have the Zalman 850W which has 6 12V rails sticker rated at 18A a piece, meaning hooking up two PIC-E connectors means I only have 36A. However, when I was looking for reviews on the PSU I came across this.

http://www.bcchardware.com/ind...0&limit=1&limitstart=1

That indicated 28A across the hardwired pic-e connectors, which would be more than enough.

Do I have enough power to run this card if I am going to go with a 275?

 

[HOOfan 1]

Originally posted by: Narynan
So, I have been looking into getting a Nvidia 275. However, one of the things I am looking at has been the power reqs for this card. It looks like I need 40A for this card. I have the Zalman 850W which has 6 12V rails sticker rated at 18A a piece, meaning hooking up two PIC-E connectors means I only have 36A. However, when I was looking for reviews on the PSU I came across this.

http://www.bcchardware.com/ind...0&limit=1&limitstart=1

That indicated 28A across the hardwired pic-e connectors, which would be more than enough.

Do I have enough power to run this card if I am going to go with a 275?

I think we see this misconception on the board at least 2 or 3 times a week.

The power requirements you are seeing for the GTX 275 is not for the card only. Nvidia is taking into account a moderately high end system that would accompany the GTX 275. That entire system (including CPU, GPU, fans and drive motors etc.) will possibly use up to 40A of 12V electricity.

The GTX 275 draws power from 2 6pin PCI-E connectors and the PCI-E motherboard slot itself. All of those source is allowed to (but will not in this case) provide 75W of 12v power. 75W*3=225W Watts=Voltage*Amps so 225W=12V*x X=225W/12V or 18.75A.

So the GTX is only allowed to draw a maximum of 18.75A or 225W of 12V power from the PSU....as you said it is doing it from three different sources though. All sources COULD be combined on a single rail, All could be on a separate rail, or the motherboard slot can be on a single rail and the PCI-E connectors on another. IF both PCI-E connectors are on a single rail, they are not supposed to draw more than 150W combined or 12.5A


Aynyway, long story short, YES THE ZALMAN ZM850HP IS MORE THAN ENOUGH FOR A SINGLE, OR EVEN DUAL GTX 275

 

[Narynan]

Yes, pretty much what I figured. But you know, would hate to buy it and not be able to return it under newegg.

Thanks!

 

[ajaidevsingh]

We are in the same boat i have a 650w Cooler master extreme power which also has 36A so i had to underclock the card quite a bit. But its still ok for the time being.

Also BTW if i dont under clock my card my screen goes blank when ever i start a benchmark...

 

[HOOfan 1]

Originally posted by: ajaidevsingh
We are in the same boat i have a 650w Cooler master extreme power which also has 36A so i had to underclock the card quite a bit. But its still ok for the time being.

Also BTW if i dont under clock my card my screen goes blank when ever i start a benchmark...

narynan is hardly in the same boat as you. He has an excellent quality power supply that would laugh at running the GTX 275. His PSU would most likely laugh at running 3 of them.

Your PSU happens to be an overrated Seventeam 500W PSU.

 

[ajaidevsingh]

Originally posted by: HOOfan 1

Originally posted by: ajaidevsingh
We are in the same boat i have a 650w Cooler master extreme power which also has 36A so i had to underclock the card quite a bit. But its still ok for the time being.

Also BTW if i dont under clock my card my screen goes blank when ever i start a benchmark...

narynan is hardly in the same boat as you. He has an excellent quality power supply that would laugh at running the GTX 275. His PSU would most likely laugh at running 3 of them.

Your PSU happens to be an overrated Seventeam 500W PSU.

Oh i did not know that. Since my Silverstone OP1200 is out of town i have to use this as a replacement for a few weeks. Oddly enough i have problems running stock Palit GTx 275 if you are rite 18.75A or 225W of 12V power should not be a problem even for a Seventeam 500W PSU that only has a athlon x2 4400+, a HDD and a wifi card to worry about...

 

[HOOfan 1]

Originally posted by: ajaidevsingh


Oh i did not know that. Since my Silverstone OP1200 is out of town i have to use this as a replacement for a few weeks. Oddly enough i have problems running stock Palit GTx 275 if you are rite 18.75A or 225W of 12V power should not be a problem even for a Seventeam 500W PSU that only has a athlon x2 4400+, a HDD and a wifi card to worry about...

That depends, PSUs derate over time. I am not exactly sure what temperature the Seventeam your 650W is based on was rated at either. If it was rated at 25C, then at a normal PC operating temperature of 40C or above, it might be significantly less than 500W.

If it is working for you now and you don't plan to use it very long, I wouldn't worry about it.

If you are not only seeing the voltage go down low, but are seeing large dips and spikes in the voltage as you are using the card, then I would replace the PSU as soon as possible.

 

[lopri]

Are you guys serious? I ran a 8800 GTX SLI with a 520W and now I'm running a PII 955BE and a HD 4890 (both highly overclocked) off of a 450W.. Surely bad PSU can cause a problem in ANY configuration, but I don't think your approach should be based on wattages. Go with a known quality PSU and you should be fine. That Zalman 850W is an excellent PSU.