How powerful should a PSU be for a PC comprising of:

P4 3GHz/FSB800
FSB800 mobo with AGP 8x, SATA, DUAL channel DDR
2x 256MB DDR400
ATI Radeon 9700/9800 Pro
M-Audio Revolution 7.1 / Audigy 2
WD 120 GB HDD 8MB cache
LITE-ON DVD 16x48
Plextor PW-482448A

I've heard anything from 300 Watts to 500Watts...
How can I estimate the correct power for this PC?

well, the main consumers are cpu and agp. there is much difference, regarding how much they consume, depending on model and manufactor (amd need a little more, just a tiny bit). generally spoken, each of them don't need more than 100 w, far less. tough your cpu is quite powerfull...
so up to here, a 350w powersupply SHOULD be enough....
BUT, if you plan to tweak your hardware a bit, you will need a higher poweroutput, 450w is recommended. same goes for areas where electical power is kind of unrelieable.
there is one advantage though, if you buy an 500w (or something like that) powersupply at the first place, you can probbably keep that for a longer time, as it got a longer compartibilty.
in short: if you got some money left, get a 450w one, far more stable overall, less chance of disturbance via power problems.
(just see to it that it's not to loud, in this class they can get awfully noisy. and some psu have 450w written on it, but they do only put out 420 or whatnot. so better inform youself about that beforehand)
hope this can be of some use...

What happens if u give a PC less power than it needs?
Will it simply not work?
Will it work slower?
Will it explode ?

nope, it will not explode (silly question).
it will mutate into an horrible alien that gonna conquer the whole world
so don't mess with power!!!
if there's way too less power, it simply won't work. but that would be unlikly.
more likly would be, that there is just not quite enough power to handle all situations (e.g. play ut2003), and then it becomes buggy. the pc either turns of, or you get some real funny behavior. in the worst case, that could lead to data-loss, or maybe even the damage of your hardware.
if you plan to buy a pc with the components above, don't spare money on the psu, you will regret it.

The most likely effect of power shortage is system instability. The system you propose is not going to require a massive power supply, 250W should be more than enough. Major requirement is that you buy a quality, heavy duty power supply and not a cheap 500w supply, for example, which will probably give you more problems than a quality 300w supply.

I totally agree with the quality issue, but not realy with your 250w proposal...
one the one hand, 300w is old standard by now, so almost nobody would sell you a 250w psu strait away (if you buy it in a store anyway).
one the other hand, the experiences that I made tell me to always go for an 300/350w one with a 'normal' pc. besides, they are not realy much more expensive, so why worry?!
In my opinion, 250w is realy not more than enough, it more lays out the minimum. what makes you think that it's enough? please back up your statement.

I'd go for a good 350W PSU, which should be enough for anything you want to do.
BTW: Seems like you are building quite a nice box there, but you really should give it more RAM. Depending on what you are doing I'd go for 1 GB.

dev0

Indeed it does look to be a nice box. Definately add 2x512MB DDR400.

I personally would be inclined to go higher than 300/350watts. Maybe it's the fuzzy-warm-feeling thing, but I would get a 480watt ANTEC True Power PSU.

It realy depends on what you are up to. if you into serious overlocking, then 450+ watts are a must. If not, 350w may be enough (s.o.)

Sorry guys!! 250w was a typo, I meant 350w.

A good PSU with 300W is enough. However, to go totally sure, get a 350W one. From reading different reviews (first and foremost in c't magazine), i can recommend Enermax and TSP (Top Selected Power). I have two TSP PSUs, solid stuff.

all right, I already thought you're living in the past, or you've gotten a hit on the head or something...

U can bet that these to brands will prolly not b available in Greece...



I'll consider it...

I have this one: ZM400A-APF Very quiet but powerful. ATM driving Athlon XP 2600+, Sapphire Radeon 9600 Pro & 8 IDE devices of which 6HDs.

I thing those components won't need more power than under 300W, but still you should get some 350W PSU. PSU best efficiency range is 30-70% of PSU max power. Using over 70% of PSU power problems are much more likely.

I'd say go for a *quality* 400 watt PSU (Antec, Sparkle, etc), and you'll be fine... not only now, but probably for any future additions as well (unless you plan to run 4+ hard drives in a RAID configuration or something). If you can afford 500 watts it sure wouldn't hurt anything...

Yes it would. If you have a "low workload" for these big PSUs (P4 3.20 GHz + Radeon 9800 + standard components: maybe ~180W idle, ~240W full load), the efficiency factor gets quite bad for 500W PSUs, because more power gets turned into heat rather than usable output. This means they also heat up your case more! Not to mention your power bill. You should calculate like this: What do i really need (300W PSU) plus safety margin = 350W, *maybe* 400W if you get a good deal.

I stand corrected...

Thats not right. 180W min. is still over 30% of 500W PSU load and efficiency is still good. PSU won't produce more heat than at full load and i think it would produce heat less than 240W load. Overall bigger PSU's are designed to work with bigger load with less produced heat, so basicly 500W PSU has smaller internal resistance than for example 350W PSU.

The ATX specification states that the efficiency factor should be at least 68% at full load. At 80% workload - 280W for a 350W PSU - the efficiency factor is around 70% with a modern 350W PSU. The lower the workload, the lower the efficiency factor gets, the worse the ratio between real power and apparent power gets, the more heat is produced in relation. To get 80% workload on a 500W PSU, there would have to be 400W workload. It's highly unlikely that you'll reach this with normal PC components, so for our high-end PC with 180~240W workload, the efficiency factor is worse, i'm guessing 50%. The PSU will not only need more apparent power, it will also produce more heat compared to a 350W model.

I can only second CiTay's recommendation for the TSP PSUs. I just build a new machine with a 350W one and it has been rocks solid and conserably quiet since then.

Assuming you don't decide to add three or four high-speed SCSI drives to your box along with a couple more optical drives, a quality 350W PSU will be overkill.

Unless you plan to overclock everything like a crazy person, in which case it'll be about right

A lot of people think that super-beefy power supplies are a necessity, when in reality this is not true - all that is really needed is adequate amperage on the +3,5&12V Rails.
Certain high-quality 250W PSUs have better rail numbers all around than lesser "350W" models, and therefore are preferable in most all cases.


Check out the PSU Calculator, which will give you a pretty realistic number so far as your power consumption is concerned.

It's based on this article by the firing squad.

As others have said, it will cause instability. I think I'm currently suffering from lack of power, and it crashes constantly when I play games. If I were you I'd go with a 430w power supply. You're almost guaranteed with 430w to be in good shape. I'm going to be building a new system with similar specs, but I'll probably go with a 550w psu because I'm looking to overclock and go with two hd's, dvd burner, and dvd-rom drive that will probably require extra power. Just go with a good company like enermax, antec, or pc power and cooling. A shitty generic 500w processor doesn't do you much good if it goes out in a week.

Altho 500W PSU efficiency is less than 350W PSU with 250W load, but still that load is not so mutch for 500W PSU than 350W PSU. Case where 500W PSU will produce more heat at same load than 350W PSU is hardly unlikely.
Do you think that PSU produces more heat in lower load than 80% of it's maximum load? Thats why too small PSU will burn becaus it will produce too much heat in too big load. Of course the heat problem can be solved couple of different ways when PSU is been designed, but that won't still remove the facts that more load produce more heat.

EDIT: Maybay i just get your point. Theoretical if 350W and 500W PSU contains same parts inside and 500W PSU bes efficiency is optimized to 80% of max load. So in this case it would be so you sayed, but in practise it's not like that. 500W PSU should contain a bit more efficient parts, witch does'nt have so big internal resistance and they produce less heat at same load. Better parts cost's more money and thats why they are not included in cheaper 350W PSU an because they are not needen in there.