Power Supply Unit (PSU) - how to choose / what is needed

talk about your computer or ask what program to use or what video card you like. others includes things like wordlists or color temps on monitor
Post Reply
User avatar
Sethioz
Admin
Admin
Posts: 4762
Joined: Fri Jul 27, 2007 5:11 pm
Custom: Gaming YT > https://youtube.com/SethiozEntertainment
Game Hacking YT > https://youtube.com/sethioz
Game Hacks Store > https://sethioz.com/shopz
Location: unknown
Contact:

Power Supply Unit (PSU) - how to choose / what is needed

Post by Sethioz »

This is a small "guide" to those who doesn't know what kind of PSU they need for their PC.
CPU and GPU are the main components that take most of the power.

people always say you have to xx amount of amps on 12v rail and blabber like this, i doubt they even know why it is like that or what they talk about.
so let me explain.

first thing you need to do is find out how much power your graphics card and cpu need.
cpus are most likely under 140w. most motherboards support cpus only up to 140w. so cpu is usually fixed, but you should still make sure how much power it takes.
GPU can take a lot of power, even over 500w. do not belive the resellers blabber about it. when i bought 1GB GT 240, then in shop they said that 400w PSU is on the limit and might burn powering it. i checked from nVidia site and 1GB GT 240 takes only 69w of power.
so if cpu takes 140w and gpu 69, then 210w is already enought, however considering that other stuff wants power too, you should consider 300w, but that's not all.

this blabber about amps on 12v rail, its simple. volts x amps = watts
so if you have 13amps on 12volt rail, then you do the following calculation. 13x12=156
meaning tht PSU that says it has 13amps on 12v rail can power 156 watt GPU if you connect it up to 12v rail.
you should consider with other components too.
some PSUs say how much amps they have on the 6-pin GPU connector, but some don't.

for example when i ordered GTX 550Ti from amazon, those idiots put into specs that "power consumption: 400w" .. these kind of things are the things you should never belive. GTX 550Ti doesn't take 400. 400 is just recommended PSU.

always check specs on official website and then add up the numbers. don't forget to give it a little reserve.
HDDs, fans, motherboard and ram and other gadgets you might have doesn't take much at all. 1 120mm fan takes less than 1w of power and same goes for HDDs. HDDs might take 1-3w maybe, but i doubt.
100w should be more than enought to power RAM, HDDs and fans. ofcourse this isn't a golden rule, keep in mind that if you have like some server machine with 100gb ram or more, then obviously it takes a lot of power.

most important about PSU, is to make sure that it has enought power on 12v rail/s. this is where you have to do the calculation. because they put it in amps, not watts. and as i said, voltage multiplied with amps equals watts. for example some 800w PSU might have less power on 12v rail than 500w PSU. wattage of PSU doesn't always mean it can power a graphics card that is like 300w.
User avatar
KEN
Special
Special
Posts: 751
Joined: Thu Jan 28, 2010 8:11 am

Re: Power Supply Unit (PSU) - how to choose / what is needed

Post by KEN »

The current GPU i have (ati HD4350) isn't connected with the psu with any power connecter.Just attached to the motherboard nothing else.
I want to upgrade to Nvidia Gtx 465.On Nvidia site they say:
  • Maximum Graphics Card Power (W) 200 W
    Minimum Recommended System Power (W) 550 W
Other specs are: Dual core E5200 @2.51 Ghz and 2gb ddr2 667 mhz ram.
According to your info my 400W PSU with 18A @ 12V rail should be enough.Or do i need a new PSU?
User avatar
Sethioz
Admin
Admin
Posts: 4762
Joined: Fri Jul 27, 2007 5:11 pm
Custom: Gaming YT > https://youtube.com/SethiozEntertainment
Game Hacking YT > https://youtube.com/sethioz
Game Hacks Store > https://sethioz.com/shopz
Location: unknown
Contact:

Re: Power Supply Unit (PSU) - how to choose / what is needed

Post by Sethioz »

400w would do, but i recommend having 500.

however most important is to see how much power it has on 12v rail. PSUs have it in amps, so calculate how much it will be in watts. you would need at least 250w on 12v rail.

also check your CPUs wattage.
i don't recommend gtx 465 tho, it's very odd and rare GPU. has more cores than newer ones, but core clock and memory clock are a lot lower. it should give similar performance as mine, but takes almost twice the power.
User avatar
KEN
Special
Special
Posts: 751
Joined: Thu Jan 28, 2010 8:11 am

Re: Power Supply Unit (PSU) - how to choose / what is needed

Post by KEN »

gtx 465 have the cost advantage and performance far more than what i require.It costs about 60% less than gtx 550Ti.So i'm going for it.

18A @ 12V rail will be 216 watts.If i need 250w then i guess i'll need a new psu.
about 22a @ 12v rail should be the right one for me. :)
User avatar
Sethioz
Admin
Admin
Posts: 4762
Joined: Fri Jul 27, 2007 5:11 pm
Custom: Gaming YT > https://youtube.com/SethiozEntertainment
Game Hacking YT > https://youtube.com/sethioz
Game Hacks Store > https://sethioz.com/shopz
Location: unknown
Contact:

Re: Power Supply Unit (PSU) - how to choose / what is needed

Post by Sethioz »

as far as i know, gtx 465 costs more than gtx 550ti. anyway this isnt place to discuss gpu prices.

gtx 465 takes 200w max, so your PSU should do. if it burns .. then you need to get new one anyway. i would give it a try. there's extra 16w on 12v rail, but problem is that GPU is not only thing taking 12 volts. all the HDDs and fans are also 12v. it might work, never know.
also some 12v wires go into mobo.

as i said i would give it a try, unless you have enought money to get a PSU too. however your problem will be CPU if you go after performance (again offtopic, but this is why i got whole new pc. cpu was too weak to get full potential out of even GT 240)
User avatar
KEN
Special
Special
Posts: 751
Joined: Thu Jan 28, 2010 8:11 am

Re: Power Supply Unit (PSU) - how to choose / what is needed

Post by KEN »

I understand.. gonna try it and see if it works :-)
Post Reply