How do I calculate the amperage on the +12V that require by GPU?

[GTHell]

Hi,

If a graphic card require 2x 6 pin or 1x 6 pin and 100-150w, how could I calculate the amperage that require by the card.

I learn that Watt is not that important anymore when it come to powerful graphic card and the The amperage on the +12V is more important.

Please help me out in case in the future someone ask me to build them a PC with newer Graphic card so I get the idea on what PSU to buy because you cannot just recommend them to buy a 150$+ PSU at all.

I got problem from the past by installing 2-3 GPU and I learnt that PSU play a big role and not faulty card or failure motherboard.

Sorry for my English.

 

[Math Geek]

amp x volt = watts. so watts / volt = amps

so 150w / 12v = 12.5 amps and so on.

and yes the psu is very important and not to be skimped on. here is a list of psu's ranking them based on performance and what they are good for. www.tomshardware.com/forum/id-2547993/psu-tier-list.html it's a good reference when buying a psu. something from the top 2 tiers is good for an overclocked machine. the third tier is fine for a normal non overclocked machine. and the rest should be avoided as not worth the money.

 

[GTHell]

Does we add up the whole system Watt usage or only GPU usage? I don't think modern graphic card will boot with 12.5 amps.
(150w system + 150w GPU) / 12v = 25a is what the real requirement for GPU right?

 

[madmatt30]

^ yes exactly that.

 

[Math Geek]

for full psu neds you have to ad it all up. cpu + gpu + other parts = total need

i use 150w as a generic "other parts". it's higher than it needs to be but this will cover the motherboard needs, drives, fans and all that extra stuff you don't think about. so cpu + gpu + 150w is a good high guess for total system needs. but don't get a psu that only has this much power. a psu works best between 60-80% of the available power. so once you have the total power need in watts or amps, divide that number by .7 (70%) to give a nice middle of the road amount for power needed.

for example: (totally random numbers here to illustrate)
cpu = 100w, gpu = 175w. so 100w + 175w + 150w = 425w total need. which is 425w / 12v = 35.4 amps on the 12v rail. now take that 35.4 and divide it by .7 = 50.6 amps. this is a good 12v amp estimate for the psu you buy to have available. so shop for a quality psu with at least 50.6 12v amps to be able to comfortably handle this system. always better to have more than less. so if a good price is out there on a psu with 75 amps, then go for it as the extra won't hurt anything nor will it add to the power bill.

 

[madmatt30]

^ overly cautious but I suppose that's a good thing for the novice builder really.
I'd be far more lax myself on both estimated cpu/mb consumption and total PSU load.

 

[Math Geek]

i am too but for the average user, it's a safe way to calculate. i get so specific as to add hdd's, fans and look for mobo reviews to see what it used as well. usage is a lot lower for sure, but for a novice, better safe than sorry. especially if you are building them for someone else like the op is saying he does. 😀

 

[madmatt30]

True mate , as someone who used to do regular system builds though what id have is a set configuration of psu's I would use ( know the rails off by heart) & pick the best unit on a per build basis.

If you're doing this with the premise of making money the the difference between say a xfx ts 550 or an evga 750w b2 can sometimes be $30-40 upwards depending on market price at the time.
Big difference in profit margin for a builder (and/or a difference in estimated build price to get the business in the first place)

100w CPU + 175w GPU would easily run on a ts 550 for example