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Power Supply for GeForce 550Ti - Understanding Requirement

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March 19, 2012 7:22:16 PM

RE: Gateway G5424 Upgrade.

Seems like a simple enough of a requirement but not knowing exactly how the power supply is used or

I have swapped out my GeForce 7300LE for a GeForce 550Ti. My current power supply is a 300W supply with 16A on 12V (I think). The 550Ti has a requirement of 400W with 24A on 12V. Therein lies the problem. I assume that factors in some safety factor for powering everything in the system and not just what the 550Ti requires.

When I look at power supplies (i.e. the Antec BP500U), they typically have two 12V rails (12V1 and 12V2), which are around 18A each. Then there is a 6 pin connector that has it's own power input.

It's not clear to me if this means that two 12V rails at 18A meets the requirement of 12V @ 24A. One the one hand the total power on 12V could be 36A but another interpretation might mean it's just 18, split over two outputs. And that says nothing about what the other 6 pin connector has.

Does anyone here know if the Antec BP500U, will meet the vague requirement of a 400W power supply, 24A on 12V by supplying 18A on both 12V1 and 12V2? Math and inefficiencies would suggest that it's not really 18A on each simultaneously, but 18A on both total. But I'm not sure. My current 300W supply has 18A on the 24, so would it even be any better?

PS: Does this power supply come with all the requisite cables. Or might I I have to buy some extra cables?
PPS: I'd like this specific question answered and not a lot of recommendations on other supplies, unless the answer is "no".
March 19, 2012 7:59:30 PM

For a system using a single GeForce GTX 550 Ti graphics card NVIDIA specifies a minimum of a 400 Watt or greater power supply that has a combined +12 Volt continuous current rating of 24 Amps or greater and that has at least one 6-pin PCI Express supplementary power connector.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the combined +12V Rail(s) is the most important factor.

The Antec Basiq Series 500W (BP500U), with its combined +12 Volt continuous current rating of 29 Amps and with one 6-pin PCI Express supplementary power connector, is sufficient to power your system configuration with a single GeForce GTX 550 Ti.
March 19, 2012 8:13:45 PM

and if you still aren't sure or want to add something else later on you can always check out http://extreme.outervision.com/PSUEngine this is a PSU calculator that is pretty comprehensive and should give you a good idea of where your power needs lie.
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March 20, 2012 12:02:53 PM

Thanks, I looked at some of the power supplies and figured out there was acumulative factor as well, when I found some that had slightly different current values for each rail. I also found a couple that listed a cumulative.

However, that said, I again, went a bit on the overkill side. :o  I decided to go with a 700W supply which is about double what I need. Bad move on my part I suspect, since my electricity bill will now be more. :) 

Thanks for the help.

March 20, 2012 4:07:11 PM

MikeSD said:
Thanks, I looked at some of the power supplies and figured out there was acumulative factor as well, when I found some that had slightly different current values for each rail. I also found a couple that listed a cumulative.

However, that said, I again, went a bit on the overkill side. :o  I decided to go with a 700W supply which is about double what I need. Bad move on my part I suspect, since my electricity bill will now be more. :) 

Thanks for the help.

The power supply will not be outputting 700 Watts 100% of the time.

If the system idles at 70 Watts, for example, the power draw from the AC wall outlet can be calculated by taking the 70 Watts and dividing it by the power supply's efficiency rating under a 10% load. If the 700 Watt power supply is 80% efficient under a 10% load then the AC power draw should be 70/0.8 = 87.5 Watts.

If the system needs 350 Watts under load then the AC power draw at the wall outlet should be 350/0.86 = 407 Watts. I used 86% as the efficiency because a power supply will have its maximum efficiency occurring at 50% load.

If a power supply has any 80 PLUS certification then there should be an efficiency rating graph available for it.
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