Confusion with dual 12v psu

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DreadCalm

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Oct 8, 2015
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Hi guys, I can't seem to find a final answer on this one and I want to be certain before I go buying anything that isn't compatible.
Basically my gf wanted a pc, I had an old mono with cpu, ram, cooler from an old rig of mine so I built her one. Current hardware is.....
Intel DQ45CB
Core 2 quad Q9500
8gb DDR2 (4x2gb 800mhz)
Western digital 500gb 7200rpm hdd (forgotten which model)
SEASONIC SS-350ET ACTIVE PFC psu.
She will mainly use this as a media rig with some very mild gaming (she likes big fish games) so although the gma on the board COULD just about cope I would like to take the strain off it with a gpu. Problem is, before I start looking I need to know what the actual psu is capable of. It has 2 +12v rails which are rated as 17A each. Does this mean I have 34A to play with? Or does it mean I have 17A to play with? Do both rails share the average that is being drawn? Or is 1 rail dedicated to certain components whilst the other rail takes care of the rest?
Only other thing that will be using power is 2 case fans, and a pci wireless card.

Thanks pc people
 
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junkeymonkey

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Nov 11, 2013
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things to look at take a 500w psu as this 2 rail it show 15 and 16 amps that's 31 amps at the 12v+ now look at a 500w single rail if a true 500w that should have 41 amps at the 12v+

2 rail 500w
http://www.newegg.com/Product/Product.aspx?Item=N82E16817182076&nm_mc=KNC-GoogleAdwords-PC&cm_mmc=KNC-GoogleAdwords-PC-_-pla-_-Power+Supplies-_-N82E16817182076&gclid=CjwKEAjwu8m-BRDM8KTcjdj8qy0SJACdjSZp9qHu7cslSHkZy-SJFqw4N_lbtjwcnnxEP4DR5Sz48RoCGH3w_wcB&gclsrc=aw.ds

single rail 500w

http://www.newegg.com/Product/Product.aspx?Item=N82E16817438012


so the multi rail is ''not '' at true amps for watts .. falls short ?


a 350w psu can only do 29 amps 350w/ 12v = 29.166 A

that's 17amps pre rail combined so 350w cant no way exceed 29 amps
 
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bigpinkdragon286

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Oct 3, 2012
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The Seasonic website for the SS-350 ET Active PFC F3 lists a +12 V Combined rating of 27 A. That's pretty straightforward and means, you have a grand total of 27 A on the +12 V rail inside the PSU. If the +12 V1 and +12 V2 are current limited, you may trigger the overcurrent protection at some point over, but close to 17 A, but unless it's specified, tested, or reviewed to have current limiting, you don't actually know that the rails rated to 17 A will actually shut the PSU down if you overload them. You can be reasonably certain the internal +12 V rail that the two +12 V outputs are derived from is current limited as per the standards, as it's a reputable brand, and exceeding the 27 A will eventually cause a shut down. If the unit was not a reputable brand, I would never assume the internal +12 V rail to implement working current limiting.
 
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bigpinkdragon286

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It's up to the manufacturer to split the overall wattage how they see fit. Older supplies had less power available to the +12 V rails while newer supplies have a higher percentage of their overall wattage dedicated to the +12 V rail. You really need to take each PSU on a case by case basis.
 
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DreadCalm

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Oct 8, 2015
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It certainly is confusing, I think my best bet is to err on the side of caution and go for a gpu that isn't particularly power hungry. A gtx 650, or a 7750 something like that. Its an old setup so I don't want to start throwing money at it when I don't really need to.
 
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bigpinkdragon286

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Maybe, but having more GPU power than you can drive now is always better than having too little, plus in the grand scheme of things, the speed of the RAM is less important than the quantity, and I would rather pay a little more for a graphics card I can continue using in the future, rather than spend half now and half later when I have to replace it if I ever upgrade the CPU.
 
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