PSU Question

[Tom1035]

Well actually I am probably 95% wrong. Anyway, Below I have created a computer. Now I am trying to figure out what power supply is needed to power the thing. Am I right or wrong?

By No means am I actually purchasing this stuff, I am doing this so I can understand how to calculate the watts required for a system rig setup. However, correct me if my system setup will actually work (If I put this together, would it even run properly assuming I have selected a proper power supply)
W = A * V


BEFORE we get started, I wanted some info on the power supply itself, here is a power supply.

http://i144.photobucket.com/al...5/Tom1035/psu_spec.jpg

Now by my calculations, that should put out (92.4 + 150 + 264) around 506.4 watts no including the negative rails.

Do we then find the voltage draw (I.E. ram and subtract it from the rail its drawing from, and then keep doing so for the rest of the computer components?

I'm madly confused, but read below, and hear out my case.





Motherboard - ECS P35T-A LGA 775 Intel P35 ATX Intel Motherboard
http://www.newegg.com/Product/...x?Item=N82E16813135059

Right off the bat, It doesn't even say it's power requirements in the system specifications....sooo...what the hell do I do now?


RAM - Kingston 1GB 240-Pin DDR2 SDRAM DDR2 800
http://www.newegg.com/Product/...x?Item=N82E16820134114

Once again, it displays its voltage draw (1.8V).


CPU - http://www.newegg.com/Product/...x?Item=N82E16819115037
Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W

Okay, already, In the title it says 65W...but also, this specifys its voltage draw which is 0.85V ? 1.3625V

Once again, I have no idea how to convert this into to watts because it doesn't have amps to multipl with?. Odviously it draws 65W. But I wouldn't know that if it didn't say 65W in the title.


Hard-Drive - Seagate Barracuda 7200.10 ST3320620AS (Perpendicular Recording Technology) 320GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM
http://www.newegg.com/Product/...x?Item=N82E16822148140

Once again, this doesn't even display the voltage draw, so how the hell can I figure out my PSU requirements?




Any insight would be GREATLY appreciated, I'm looking to upgrade my system at some point, I just used this as a test project. I have no intent on buying any of the crap I posted above.

Thank you ahead of time.

Tom

 

[panfist]

Firstly, I'm not sure what you're calculating with the following quote: "Now by my calculations, that should put out (92.4 + 150 + 264) around 506.4 watts no including the negative rails." If that's supposed to be the combined power of the 12, 3 and 5V rails, they don't always add up exactly. For example, the 12V rail can only output 264 watts provided that you are -not- maxing out the 3 and 5V rails.

Seconldy, that PSU is definitely enough for that system, probably by about 40%.

When calculating your power requirements it's better not to bother with the exact voltages and just overestimate by a healthy amount. I usually take the max rated power for the CPU and double it. Triple it if you plan on overclocking. That more than covers the cpu, motherboard, and RAM. Hard disks use a pretty small amount...add about another 20 watts per hard disk. That's overestimating by about double.

Next, I don't see a video card anywhere in your list. That should use about another 50-150 watts depending on which one you get. Again, this is a healthy overestimate...unless you get a top-end enthusiast part.

So...in your case that PSU is more than enough by a good amount.

P.S. I must recommend that you buy at least 2GB of RAM. Why spend $200 on a CPU and then cut a major corner on RAM? Spend $20 more on RAM and you will notice a major difference in performance.
Here's a link to a newegg search for 2x1GB DDR2 800MHz...
http://www.newegg.com/Product/...tion=&Ntk=&srchInDesc=

Any of those should do.

 

[mpilchfamily]

Take a load off your mind and use a PSU calculator.
http://www.extreme.outervision.com/

You need to figure out what video card you want. The main things you are looking at are the Video card and CPU. Those will determine the PSU you will need since they are the items that use the most power. Typically the video card comes with a recommendation for the amount of power you need. This is generally stated in amps and is referring to total system power and not just want the card needs. Based on an average system of course. So i higher end CPU will require a bit more. The above linked PSU calc will give you a ruff idea of the amount of power the system will need. The numbers it produces are a bit high. But its a decent enough reference. Just take that reference and match it to a good quality PSU and your set. This forum is full of threads listing quality PSUs and the kinds of systems they can support.

 

[tcsenter]

Originally posted by: Tom1035
http://i144.photobucket.com/al...5/Tom1035/psu_spec.jpg

Now by my calculations, that should put out (92.4 + 150 + 264) around 506.4 watts no including the negative rails.

Amps are loading current, watts are dissipated power. The amp rating for each rail is the maximum load that can be placed on that rail, when the other rails are at minimum regulation load.

IOW, +12V can handle up to 22A ONLY if +3.3V and +5V are at minimum load. +3.3V can handle up to 28A ONLY if +5V and +12V are at minimum load. So on and so forth.

Total DC output is 400W max. -12V and +5VSB are good for 20W, leaving us with a budget of 380W max for all three primary rails. In a contemporary ATX12V consumer PC, you can safely assume that +3.3V and +5V combined will never exceed 150W. That leaves us with about 230W (19A) on the +12V rail that is guaranteed no matter what is going on with +3.3V and +5V. Since this is a Seasonic unit, you can round that up to 20A if you like nice even numbers.

Once again, I have no idea how to convert this into to watts because it doesn't have amps to multipl with?. Odviously it draws 65W. But I wouldn't know that if it didn't say 65W in the title.

It dissipates 65W, not "draws" (that would be amperage). 65W = 65W. You can then divide that by any nominal voltage assumed to be the supply. In this case, 65W / +12V = 5.5A (rounded). This is less precise than digging into the processor datasheet to find the absolute maximum amperes at any given load-line and temperature assumption, but we're not building a pacemaker. Its close enough for puters.

Edit: oops, I forgot VRM loss. Since processor TDP is on the output side of the VRM, and we are estimating power on the input side, we need to account for voltage regulator efficiency losses. A safe way to do that is to multiply the amps derived from TDP by 1.20 (20%). e.g. 5.5A x 1.20 = 6.6A (I would call it 7A and be done with it).

 

[Tom1035]

Thank you for your information, seems a bit clearer now. So the bigger the PSU the better, If you have the cash of course

 

[tcsenter]

Depends on what you mean by "bigger". "Enough" can be as good or better than "bigger".