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Ive just recieved my GTX 480 and new mid price (£70) 800W PSU but i'll be away from my workstation for a few days so cant install it. Just reading up on the spec for the 480 and already knew it needed over 600w PSU and did read somewhere about it needing 42A but thought an 800W PSU should be enough just to run this card and a basic Q6600, 6GB RAM, 1 HD, 1 dvd drive system. However my PSU seems to have 4x12V readings all of which are max 20A! So does this mean that its no good by a long shot and I need to return it straight away and exchange for a silly money PSU? I don't want to throttle the 480 as that would be defeating the object but really dont want to have to send it back if i dont need to. It does say minimum requirements are based on an intel i7 3.2ghz system which im guessing draws more power than my little q6600! But all that might be irrelevant if the 42A is the only important figure in this case.

Thanks for any help on this, never really paid too much attention to PSUs before.
Rob

There has been a lot of 'talk' going on recently about GTX 480 PSUs. Nvidia isn't helping it either!!
Yes Nvidia recommend 42A at 12 volts. However, they don't say whether that 42A must come from one whopper 12V rail or multiple rails.
A few macho cards have a single 80A+ rail (some higher even) but if you check through:
http://www.slizone.com/object/slizone_build_psu.html

you'll see a few Enermax and Thermaltake cards are SLI certified.
These are some of the most reputable cards and they don't not have any 42A rails (they use multiple 30A rails).

see these forums:
http://forum.thermaltake.com/viewtopic. ... 7411956140
http://forums.nvidia.com/index.php?show ... 5803&st=40
http://www.overclock.net/power-supplies ... n-gtx.html

So indeed it seems it's the total of all the rails.

A £70 800w PSU sounds relatively cheap. You say it has 4 12V rails that each deliver 20A?
Does the PSU give a figure of the combined wattage for all 12v rails?
If you multiply 4x12x20 you get 960...and you've still to add on the 3 & 5V rails.
Quite often the the max combined wattage is less than the sum of the constituent rails... so I wonder if you have 80A to play with.


That said you've got if you've got 2 12v 20A rails and they can both actually deliver 20A when combined then if you you should come pretty close.
Is it 80+? Does it have both 8 & 6 pin connectors for the card? A set may have come with your card.
Realistically it will 'probably' run the card, but if you can still exchange it I would, for something 80+ if you love mother earth or pay the power bills

You will probably be ok. Easiest way to figure out what you'll need is to take the amount of watts needed by the card, something like 230 watts if I remember right) divide that by 12. That will tell you the amps needed, which if the needed watts is right is about 20amps. I would imagine that the 2 power connectors needed for the card would be on different rails, but you never know with some PSU makers. If you you were doing SLI, or dual gtx480's then you would need to look at a larger PSU with more amps.

Thanks guys, its a bit of a mine field. Yes there are two sets of 8+6pin connectors, its a modular PSU 900W peak 800W constant - http://www.ebuyer.com/product/135196. It has come with these two sets of cables attached to ports on top of each other not side by side as it were but there is an 8 pin socket at the end I can stick one of them into - basically I dont know if it is currently set up with them both coming from one rail or not and there aren't any instructions! To be on the safe side I will put one of them on the end one. So should I take the 8 pin from one and a 6 pin from the other? No chance i'll be running two cards so using both cables doesn't matter. Would that then leave me with a combined 40A - still 2 short but wonder how much of a difference it makes? How will I know if there is a problem? I imagine if the psu shuts down under load then there is a problem but if its close enough to the required power is there a chance the card will just run slow and is this something which can be measured on the trench bench test? What should I be aiming for again with a 480? I think Ive read it depends on the drivers which muddies the waters a bit!

Use the second cable for the second power plug for the gtx480. You should be fine. If it is drawing too much power from the PSU, the PSU could fail after awhile. It should start heating up quite a bit before that though. The gpu might also just not power up. The numbers always have some fudge room as PSU's can't always deliver their rated specs and there is so much tolerance in component values that things aren't always, if ever, what they are stated to be. Everything should run fine. I doubt youd see any performance differences other then excess heat or not.

Thanks man ill give it a go when I get back. Fingers crossed it will be able to tame the beast!