watts vs amps

Xfx Radeon hd 4850 1gb ddr3 dvi/vga/hdmi
June 26, 2010 at 18:17:03
Specs: Windows 7
why do ppl say that the wattage on a power supply for a graphics card doesnt matter as much as the amps u get on a single or dual 12v rails? i have a 350 watt dell atx ps unit that has an 18amp max on each 12v rail...the radeon card says it needs 450 watts but makes no mention of amps....i have been told my dell 350watt ps can run this card...can it?
currently running a delta power supply in my asus 300watts 10a max on 12vA and 14a max on 12vB. that power supply isnt enough i dont think tho im running an xfx nvidia 9400 gt graphics card on the delta 300 watt ps unit now where the 9400 box says it recommends 400 watts and i have no issues. whats the deal here for an electronics n00b? lol ty XD

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June 26, 2010 at 19:05:14
When a manufacturer recommends a certain wattage power supply, it's for the entire system including the card, not for the card alone. Some manufacturers include an amperage requirement for the +12v rail as well. That's because majority of the power that goes to the video card comes from the +12v rail. But other components "feed" off the +12v as well. For example, the CPU get's 100% of it's power from the +12v, so if you have a CPU rated at 125W, it needs up to 10A. A gaming video card can easily require between 6-12A, depending on the card. HDDs, CD/DVD drives & all fans use the +12v too, so you can see that having adequate amperage +12v rail is critical to troublefree performance.

You are NOT going to be able to run the HD4850 on a 300-350W PSU. I responded to one of your other threads & included a power consumption chart showing many modern video cards. Do NOT choose a card that takes the power supply close to it's limit. A system running a HD4850 is rated at 268W...that's a little to close for comfort with a 300W PSU.


BTW, you didn't have any problems with the 9400GT because it's a low end piece of sh!t, not a gaming card. It draws about 35W under full load (less than 3A on the +12v).

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