# Rated PSU Amps and Wattage

Discussion in 'General Hardware' started by Relinquish, Apr 27, 2012.

1. ### RelinquishNew Member

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Hello,

I was confused about something so I was wandering if anyone can help me out.

Basically I have an OCZ 550W Fatal1ty PSu and whilst I don't have an issue with it, I was wandering something about the advertised amperage ratings. On the side of the PSU it says that there are 2 12V rails, each with a rating of 25 amps with a total advertised output of 450W (The other 100W is for the 5V and 3V rail).

Is that not off?

If I use the equation: power = voltage X current I get 12 volts X 25 amps = 300W per rail. So 600W for both rails no?

I ask because Corsairs TX650 has 52 amps on a single 12V rail and is rated for 624W of output. Also I want to know what flexibility I have in terms of adding a decent graphics card (my one has been RMAd). I mean 150W is quite a big difference and will allow me a lot of breathing room. It may even be a misprint.

2. ### Cotton_Cup

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550/12 = 45.8 so should be getting 45amps

25amps each should not be that bad overall should be like 40amps or so in total if I'm right.

imo if you can find one at a single 12 rail go for it. as single rails are more effective at least based to the peoples socks I've been smoking

3. ### Naito

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From what you're saying, your PSU can supply your system with 450w over two 25amp, 12v rails. The rails themselves can handle up to 25amps each, but using this formula, I = P÷V, we can determine your system can supply a total of ~37.5amps on its 12v system (overall, not per rail). When picking a PSU, amperes it can supply over the 12v subsystem, is arguably the most important thing to look for.

It's often hard to find ampere recommendations of a GPU, but to give you an idea of my setup (look at my 'System Specs'); it'll pull a max of ~400w+ for the whole system under load (Prime95 CPU, MSI Kombustor Xtreme burn-in GPU). Using this information, I can determine my GTX 470 uses ~220 watt under load. Combined with a manufacturer rating of 42amps needed. I may not be able to use my system with your PSU, but a higher wattage PSU, yes.

4. ### de.das.dudePro Indian Modder

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both are 25A?

there is a 90% chance that it isnt even a dual rail.

also i suspect that the max output on either of the rails at a time is 25A.

it says 450W so you have 37A on the 12V rail as a combined output.

so if you deduct 150W from 450W for CPU and stuff, you can easily run a 250W graphics card.
goto http://www.gpureview.com/show_cards.php/ to findout about graphics card power consumption. They have a really extensive database.

5. ### FourstaffModeratorStaff Member

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You can probably draw 25A from either rail but not full 50A from both. At least that is my understanding.

6. ### de.das.dudePro Indian Modder

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yeah, like i said too.

7. ### Cotton_Cup

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