Video card 12v rail amps question.

[GLD]

My question is that does a single ATI X1800/X1900 series card really need a psu with 30 amps on the +12v rail? Or is that really the requirements for a crossfire setup. 30a for 1 card sounds so high. I just got a PNY 7900GS and their site says: A minimum 350W system power supply (with 12V current rating of 20A)
For two GeForce™ 7900 GS-based graphics cards running in NVIDIA® SLI™ configurations, a minimum 450W system power supply (with 12V current rating of 26A) is recommended.
That seems like a huge difference to me.

[randomperson21]

that does sound high. i'd say 20-25A

[JC316]

It's an insurance policy so to speak. I was running an X1800GTO on a 450W with 20A rail and it did work, until I tried to OC. Does it NEED 30A? Probably not. Is it best to have 30A? Yeah.

[Namslas90]

I have a X1900XTX, after reading the requirements that came with the card, I made several calls to ATI. Eventually I got a third level tech who said the minimum requirements for a single card is 18amps, however that the better newer games ( DOOM 3, F.E.A.R., QUAKE 4, and newer online games) you should have at least a minimum of 22amps. If running Duel X1xxx cards in crossfire mode you should have 32 amps available. However, with the release of the X1950 series they have lowered the requirement to 22-28 amps. I Have 22amps and don't have any problem running any games set on the highest quality(ultra).

[HeavyH20]

The PSU specs required have changed to amps versus watts since so many low end power supplies effectively cheat their wattage claims. This is accomplished through high 5V and 3.3V outputs you will never use and chinsing on the 12V rail capacities you really need. And, if your PSU is rated at 20 amps max, you will never want to use 20 amps. Ripple, heat, and inefficiencies will affect your system negatively. Instead, you'd be better off with a 30 amp plus PSU so that you stay well within the limits and avoid any issues. Best bet is to stay away from the dual rails, as they can be hard to balance the loads. Look for a good single rail PSU with 30 amps plus.

[Namslas90]

@ Heavy H20
I agree, which was also one of my questiones to ATI. Also, they related to me the difference of the 12vrail amps verses total amps of the PSU. One of the ATI techs said the card rating was for the 12v rail amps and the higher level ATI Tech said the total PSU Amps. What the real requirement is was never made clear!!

[HeavyH20]

Interesting. Since the card uses about 125 watts under full load (the 7900 GTX is 85 watts), it works out to be about 10.5 amps for the card, itself. Assume a 65% load target, and all you need is a PSU to supply around 15 amps on a single or dedicated power rail for the video card. A 30 amp PSU should be more than enough for the system.

[Gwargor]

Get as many amps as you can. More than just your Video Card draws from the 12v..Like your CPU. I've seen over 32amps in ATI tools when in 3d mode on my X1900XT.

[Zubasa]

Interesting. Since the card uses about 125 watts under full load (the 7900 GTX is 85 watts), it works out to be about 10.5 amps for the card, itself. Assume a 65% load target, and all you need is a PSU to supply around 15 amps on a single or dedicated power rail for the video card. A 30 amp PSU should be more than enough for the system.

Thatz good, since I have a +12V rail that supply 15 amps an another 14amps.
Well, I dont own a high end card so thats not a concern for me.

[ARTOSOFT]

Guys, guys. The GPU itself doesn't work on 12v. It is only ~1.7v. If say ATITool report current 25A, its only take:
~1.7v x 25A = 42.5Watt.

Regards,
Arto.

[Zubasa]

Guys, guys. The GPU itself doesn't work on 12v. It is only ~1.7v. If say ATITool report current 25A, its only take:
~1.7v x 25A = 42.5Watt.

Regards,
Arto.

Oops!
Lol what were i thinking!
Most CPU's run below 1.5 volts. 12 volts is just too much for chips.

[HeavyH20]

No kidding, but 12V is supplied to the card and converted by the video card internally. Normally, lower end video cards work exclusively on bus voltage of 1.5V (you can see that in your BIOS which you can adjust upwards). The high end cards use supplemental power. The X1950XTX card draws 125 Watts of total power for operating. So, you can assume 60 watts average to 75 watts max supplied by the PCI-E bus (42 for AGP), so you need a PCI-E power connector (12V) to supplement. Each one provides up to 75W. So, again, we are still looking at about a 10 amp draw on the whole system against the 12V rail(s).