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Do bigger PSUs - e.g. 600w always draw more power?

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imported_boe

Senior member
I'm thinking about building a new PC. It is for home and will be on quite a bit. I don't want to put a massive PSU in it if it is going to use unnecessary electricity.

I'm thinking about a 4800 x2 and a system that will support SLI or crossfire along with 2 hard drives.

I think it would work with a 500 watt power supply but if a 600 watt power supply doesn't draw any more power unless the system requires it, I would get a 600 watt power supply.
 
Hi, Current draw is determined by the load and not by the Power Supply. It will be slightly less efficient than the smaller one, but probably not noticeable. Hope this helps, Jim
 
It depends on the effeciency rating. Cheaper power supplies are tested at lower temperatures. More expensive, or more well known power supplies have high effiency at high temperatures.
 
Just as a point you don't need a 600W PSU, it won't do anything that a 500W one won't and it's plain and simple a waste of money for you.
 
Originally posted by: Bobthelost
Just as a point you don't need a 600W PSU, it won't do anything that a 500W one won't and it's plain and simple a waste of money for you.
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I would need some sort of PSU calculator to know for sure what I need. Does anyone know of one? With APC UPS - you can figure out what you need by puttling in what type of equipment you will use. Something like this for PCs would be handy.
 
There are a load of them around, but the short version is that your PC will not draw so much as 400W at full load.

Look at the review of the Fx-60 on the main site, the system draw for the P4 was less than 300W at full load, and that's the power drawn from the wall not the PSU itself.

A 500W PSU will be enough, just make sure it's a good brand (Seasonic, Fortron, PCP&C, enermax etc.)
 
Originally posted by: Bobthelost
There are a load of them around, but the short version is that your PC will not draw so much as 400W at full load.

Look at the review of the Fx-60 on the main site, the system draw for the P4 was less than 300W at full load, and that's the power drawn from the wall not the PSU itself.

A 500W PSU will be enough, just make sure it's a good brand (Seasonic, Fortron, PCP&C, enermax etc.)
Click to expand...


Thanks - I'm currently considering the enermax noisetaker. IF you could post a couple of the better PSU calculators I'd really appreciate it. The one on the enermax web site only lists old components - hard to do a realistic estimate - but it comes out about 617 watts.
 
I'm a bit hungover so i'm afraid i'll just point you towards the search engine at the top of the page 😉

Noisetaker isn't a bad PSU but which you should choose does depend what you want the PSU to do for you.
 
Originally posted by: boe
Originally posted by: Bobthelost
There are a load of them around, but the short version is that your PC will not draw so much as 400W at full load.

Look at the review of the Fx-60 on the main site, the system draw for the P4 was less than 300W at full load, and that's the power drawn from the wall not the PSU itself.

A 500W PSU will be enough, just make sure it's a good brand (Seasonic, Fortron, PCP&C, enermax etc.)
Click to expand...


Thanks - I'm currently considering the enermax noisetaker. IF you could post a couple of the better PSU calculators I'd really appreciate it. The one on the enermax web site only lists old components - hard to do a realistic estimate - but it comes out about 617 watts.
Click to expand...

the online psu calculators are hit and miss. the information listed here is the better, imo over the online calculators. just get a good brand of ~500W and you will be good to go for just about anything short of the serious server with dual dcs and dual gpus with numerousl 15k rpm scsi hdds and tons of ram that some people run for real work and hardcore rendering.

also, the efficiency rating is what you need to worry about about and at what temp because as the temp goes up the effiiciency goes down.
 
Generally, it will draw more power, due to not being as efficient at very low or high draws, but not that much more. Check out reviews at SPCR.
 
Originally posted by: potato28
It depends on the effeciency rating. Cheaper power supplies are tested at lower temperatures. More expensive, or more well known power supplies have high effiency at high temperatures.
Click to expand...

Noit exactly true.....there is more to this efficiency rating stuff than we have space to get into it.
 
i calculated with the calculator and at 100% peak load (and i added an extra 5 things to make you feel safe) it's at 509 watts and you will never hit 100% peak so 500w should be safe
 
Hi, Bobthelost has it right, but look at it this way, while you are not running the comp you can use the power supply for an arc welder.
 
Gotta agree with everything Bob's saying here.

A bigger PSU will usually draw more power from the wall. That's because PSUs are a little more efficient when they have a load on them. Most PSUs have their peak efficiency between about 55%-85% load. It drops off a tiny bit at 100% load, and usually drops off more significantly at extremely low loads.

For example, say JimmysPSUs all have these characteristics (similar to an Antec True Power PSU):

65% efficiency at 25% load
68% efficiency at 40% load
74% efficiency at 70% load
71% efficiency at 100% load

So, say your machine draws 240W. If you have a 350W JimmysPSU, you will pull 324W out of the wall. If you have a 600W JimmysPSU, you will pull 353W out of the wall to get your 240W. It's not that much of a difference, but it's like leaving a light on several hours a day that you don't need to.

This isn't always true, though. A lot of manufacturers have PSUs which are almost identical except for a tiny bit of beefing up for a bigger wattage. A lot of 600W PSUs will be just as efficient with a 200W draw as their 500W counterparts will be with a 200W draw. That's because they're almost the exact same PSU.

But I wouldn't worry about losing efficiency just from your PSU being too big. The difference between quality of PSUs is much more important.

For example, let's look at some different PSUs with a 150W load on them

SeaSonic S12 500W = 85% efficiency = 177W AC draw
Cooler Master Real Power 450W = 80% efficiency = 187W AC draw
EnerMax Noisetaker 475W = 79% efficiency = 189W AC draw
Fortron Blue Storm 500W = 79% efficiency = 190W AC draw
EnerMax Noisetaker 600W = 77% efficiency = 195W AC draw
OCZ ModStream 520W = 77% efficiency = 196W AC draw
OCZ Power Stream 470W = 76% efficiency = 197W AC draw
Fortron Aurora 350W = 69% efficiency = 217W AC draw
Antec NeoPower 480W = 68% efficiency = 220W AC draw
Antec True Power 380W = 68% efficiency = 220W AC draw
HighPower 300W = 66% efficiency = 227W AC draw

Antecs are pretty good and they're a good deal with a case. Fortrons are decent and they're pretty cheap. Some people seem to think that any old Antec or Fortron PSU is among the best, though, and they're not. The Blue Storms are great, but I'm not going out of my way to get the other ones.

Antecs aren't bad at all, though. Keep in mind that most of your generic PSUs are going to claim a peak efficiency of 70%, but good luck getting it.

I don't know that efficiency itself is that big a selling point, though. I'm impressed with SeaSonics and Blue Storms because of the build quality, low noise, reliability, etc... But saving 50W of power... sure, that's a lot. It's like leaving an extra light bulb on 24 hours a day next to your computer. But it would take a few years to pay for the extra price of the PSU.
 
Originally posted by: Tostada
But saving 50W of power... sure, that's a lot. It's like leaving an extra light bulb on 24 hours a day next to your computer. But it would take a few years to pay for the extra price of the PSU.
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50w for 24hours a day, every day of the year would cost around $40 a year with a price of 9 cents per kwH.
 
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