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Difference between Max and Peak Amperage rating

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April 16, 2010 8:11:35 PM

In the specification of one PSU, the max amperage for a 12v rail was mentioned as 25A whereas peak amperage was mentioned as 30A. What is the difference between the two? How much power can be drawn from that rail, 300W or 360W? (a 6-pin and an 8-pin connector were connected to the rail).
a b ) Power supply
April 16, 2010 8:29:22 PM

It means it can have a sustained output of 25 AMPS but could push 30 Amps if conditions permit it like how hot the unit is and over time PSU will degrade over time and will not be able to output as much as they would have brand new. If you are looking into buying a new unit list your specs and I can help you pick out one suitable for your system. If you are trying to figure out if your PSU can run your system list your specs and the make and model of your unit.
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April 16, 2010 8:37:18 PM

So such a PSU can support heavily OCed 5970? (Assuming one rail is completely dedicated to GPU)
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a b ) Power supply
April 16, 2010 8:39:26 PM

What 30 Amps hell no it will not support a 5970 You will need to at least have 48 Amps on the 12 volt rail 54 Amps is recommended especially if you are overclocking.
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April 16, 2010 8:42:28 PM

I meant CPU and other components are connected to another such rail and only a 5970 is connected to one rail.
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a b ) Power supply
April 16, 2010 8:49:49 PM

It doesnt really work that way they say they are separate but they still will use a combined output but if you have a PSU with 2 12v rails each putting out 30 Amps then your fine it will run it.
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April 16, 2010 8:58:16 PM

I know how that works. I just wanted to know if one such 12v rail can output more than 300w or not if required for a short duration of time. Thanks for your reply.
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a b ) Power supply
April 16, 2010 9:09:20 PM

Sorry I was misunderstanding your question it really depends on the PSU like if its a seasonic, corsair or one of those great PSU's they are known to be able to put out more then what it says but if its a cheapo then you will be lucky to get 25 Amps out of that rail.
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a b ) Power supply
April 17, 2010 3:31:23 AM

what psu is it?
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a c 144 ) Power supply
April 17, 2010 3:59:12 PM

For all practical purposes, the "30 amps peak" rating is a figment of an advertising copywriter's imagination.

And a total of 25 amps is not enough to run a 5970 and the rest of the system. A 5970 be itself needs 20 - 25 amps.
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a c 248 ) Power supply
April 18, 2010 4:15:09 AM

+1 what jsc said.

Unlike the rest of the ATI radeon HD 5000 series video cards, the 5970 is a power hog.

There appears to be a misunderstanding about multiple +12 volt rails. True multiple +12 volt rails were designed for very high end, very high wattage power supplies. There are only a few of them.

With one exception, the lower wattage power supplies do not have true multiple +12 volt rails. Instead, think of them as "virtual rails". It was an advertising gimmick to increase sales. There was a big stink about it a few years ago.

If you would like to learn more about multiple +12 volt rails, then here is a link to an excellent explanation at jonnyguru.com:

http://www.jonnyguru.com/forums/showthread.php?t=3990
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