Why you dont need 500 watts

~El~Jefe~ · Post by **~El~Jefe~** » Tue Apr 12, 2005 9:53 am

Ok, well here is something that hasnt been pointed out for a while.
Efficiency and temperature.

You WILL need 500 watts if you have hot air moving into the psu from the case. an isolated, open breathing psu doesnt get hot and therefore, puts out much more wattage of power at higher draws.
You WILL need 500 watts if your psu is not efficient. Take the phantom. It is so efficient that it truly gives nearer its wattage amount for every demanding draw. This does 2-fold, it lowers its own heat evolution, which helps its efficiency again. However, it is fanless. So, if properly cooled it would take care of multiple hardrives, lots of pci cards, lots of ram and a decent video gaming video card. I would guess even the 6800 ultra.

People will disagree with this, but a properly built machine's benchmarks just show this..... You dont need 2 video cards for ANYTHING. ever look at the benchmarks? it would do people better to get a regular non ultra 6800, and just go and get a 3500 90 nm a64. its a cheaper option all around, and give people insane framerates. One day, sli, youll need. by then, your system will be trash compared to those requirements, and your vid card will need 512megs minimum, etc etc...

If you want to get a 430 working for near 400 watts, you need to isolate it from the case. I have now a year of working with this stupid bottom fan mounted psu (vers A2 seasonic 400 watts). It is impossible to silence. Everything that evolves heat gets sucked up into it. 120 mm is a great idea, but having the psu heat up from case temps isnt. If I could isolate it (not in this case) then I would be running quiet (a2 runs quiet doesnt ramp if kept cool).

tay · Post by **tay** » Tue Apr 12, 2005 11:22 am

You should read the PSU fundamentals on this site coupled with a healthy bit of googling before making these comments as you leave out a bit of nuance. Things are always a little bit more than they seem and making generalizations (as I am about to do) generally (:oops:) leads to trouble.

All the testing here is done at peak load with the load blowing all the hot air into the case. So when a 430watt seasonic s12 is tested for example, 430 watt of heat are being blown into the case, along with some 120mm fan pulling air out. Read the review and PSU fundamentals. Sure temperature/efficiency matter, but only to a smallish degree for most of the quality PSU makers.

As others have mentioned here before, most (not all) people buy 500watt PSUs for the same reasons that they buy Chevy Yukons or Tahoes or whatever. Im not implying that noone has a need for a 500w unit, but the need is not for the reasons you mention. If you are planning on getting a dual core prescott, 4HDDs, with a 6800ultra sli, you really do want a 500watt unit.

If not, heat or no heat, the 430W unit provides a good amount of headroom for the vast majoriy of systems.

Devonavar · Post by **Devonavar** » Tue Apr 12, 2005 2:48 pm

tay wrote:So when a 430watt seasonic s12 is tested for example, 430 watt of heat are being blown into the case, along with some 120mm fan pulling air out.

Not sure which 120mm fan you're talking about. The PSU bench has a low speed 80mm exhaust fan in addition to whatever airflow is exhausted through the PSU.

frankgehry · Post by **frankgehry** » Tue Apr 12, 2005 2:58 pm

What about the "evacuate the heat" role for the psu? MikeC started this thread a while ago but it didn't really seem to catch on because bottom suckers seem to have taken over. Is there no situation when a seasonic super silencer would be preferred over an S12? - FG

StarfishChris · Post by **StarfishChris** » Tue Apr 12, 2005 3:23 pm

Straight-through airflow is easier to duct and eliminates the 'fans-fighting-for-air' situation, but you can only fit an 80mm fan at the back. Now, if there was an efficient PSU with two slow-moving 80mm fans...

frankgehry · Post by **frankgehry** » Tue Apr 12, 2005 3:34 pm

S,

You mean like an OCZ power stream configuration with two inline 80's only efficient and quiet? - FG

StarfishChris · Post by **StarfishChris** » Tue Apr 12, 2005 3:53 pm

No, more like two in parallel. It would have to be done at the front otherwise there would be no room for power cables.

Tibors · Post by **Tibors** » Tue Apr 12, 2005 4:22 pm

You'll never find two 80mm fans in parallel in a commercial PSU that conforms to the ATX spec. Simply because it doesn't fit. A PSU is a little under 15cm wide. So you'd end up with two 70mm fans and since nobody ever found quiet versions of those.....

You can do it yourself though.
http://forums.silentpcreview.com/viewtopic.php?t=15726

tay · Post by **tay** » Tue Apr 12, 2005 5:58 pm

Devonavar wrote:Not sure which 120mm fan you're talking about. The PSU bench has a low speed 80mm exhaust fan in addition to whatever airflow is exhausted through the PSU.

Thats the one i meant thanks!

WRT 80mm/120mm people here have gotten both to work if the basics are there with many people prefering the 120mm for its extra exhaust function. The dual 80mms on the inside or even just a simple 92mm on the inside sounds like a cool idea.

frankgehry · Post by **frankgehry** » Tue Apr 12, 2005 6:01 pm

That's very clever - Thanks

~El~Jefe~ · Post by **~El~Jefe~** » Tue Apr 12, 2005 6:28 pm

sometimes, people on the forums do better with broad generalizations instead of reading (or not reading as it seems) the longer threads of eons past on psu's and other things. That's why they ask about 500 watts, and thats why I made this post. So I can not see it posted yet again.

120 mm fans on the bottom of psu's is a bad idea if its sucking all the air from the machine. It ramps up at will, which increases its sucking of hot air, which, well makes it suck. My psu in normal window's/emailing/mudding lil stuff mode can quiet down if I LOWER the output from my exhaust fan. Apparently, the heat is getting caught in some sort of negative pressure bind.
So, in order to decrease the heat that is comming into the bottom of psu, I would have to remove more heat, but i cant as this generates more heat in my psu....

positive pressure would help, yet that means adding a fan to the front.... alot of fans going on already... (i doubt how much it woud help as I am guessing that the fan in front would have to be pushing more air than my exhaust, which isnt really feasible being that a pabst 120 is on rear and 120 on psu.

dano · Post by **dano** » Tue Apr 12, 2005 7:52 pm

Yeah chief, broad generalizations are great for everyone. Not only do you not know weather someone has SLI and a high powered pentium with a raid array, but you back up your claim that generalizations are good with an example from your own computer. Isn't that the definition of specificity? This whole thread is complete rubish that was created entirely so chief could preach and feel good about his knowledge and slam people who were looking for good performance out of their machine ("You dont need 2 video cards for ANYTHING.").

Talz · Post by **Talz** » Tue Apr 12, 2005 7:56 pm

~El~Jefe~ wrote:You WILL need 500 watts if you have hot air moving into the psu from the case. an isolated, open breathing psu doesnt get hot and therefore, puts out much more wattage of power at higher draws.
You WILL need 500 watts if your psu is not efficient.

You have a good point that heat effects efficiency, but it is not such a dramatic effect. The main thing it's going to do is make the cooling fan run faster/louder, not require gobs more power.

~El~Jefe~ wrote:If you want to get a 430 working for near 400 watts, you need to isolate it from the case. I have now a year of working with this stupid bottom fan mounted psu (vers A2 seasonic 400 watts). It is impossible to silence. Everything that evolves heat gets sucked up into it. 120 mm is a great idea, but having the psu heat up from case temps isnt. If I could isolate it (not in this case) then I would be running quiet (a2 runs quiet doesnt ramp if kept cool).

There are solutions, water cooling cpu/gpu with external radiators will take a lot of heat straight out of the case. A case with a seperate PSU channel/compartment can also do tons of good here. It's not needed but even a somewhat normal high load system will be easier to silence if you can use any of those tools. You can even use sound deadening materials to counter this to a small degree.

Solid Snake · Post by **Solid Snake** » Tue Apr 12, 2005 10:03 pm

You dont need 2 video cards for ANYTHING.

No? Not even for a dual-head setup?

luggage · Post by **luggage** » Tue Apr 12, 2005 11:00 pm

Solid Snake wrote:
You dont need 2 video cards for ANYTHING.
No? Not even for a dual-head setup?

You mean 4+ monitors?

lm · Post by lm » Tue Apr 12, 2005 11:57 pm

My dualhead setup has 2 monitors connected to a single video card.

A 120mm fanned psu would rock if it was located on the bottom of the case, so that it would draw it's air through a hole in the bottom. The case probably needs high feet, and preferably an air filter, that could be the size of the whole bottom of the case, to reduce air resistance to minimum.

Bluefront · Post by **Bluefront** » Wed Apr 13, 2005 2:36 am

~El~Jefe~.....I'm fairly certain your statements in this thread are well-meaning, but they are only your opinions, and should be labeled as such. There are plenty of examples of cooling systems that dispute your opinion.
I'm posting right now using a P4-2.66 that runs on one fan....a bottom facing 120mm that sucks through the CPU heatsink and blows into the PSU that has had it's fan removed. It's quiet...never overheats. The only other fan in the computer is a small fan between the hard drives.

So how does this computer fit into your idea of effective, low-noise computing?

Post by **Rusty075** » Wed Apr 13, 2005 4:39 am

If your low speed PSU fan, and your low-speed case fan are fighting for air from each other, that's more a sign of poor case ventilation than an inherant flaw in 120mm fanned psu's.

I've assembled numerous systems with 120mm psu's and fans, and they typically exhibit the opposite fan relationship: speed up the exhaust fan and the PSU fan slows down. The difference is likely that all of those systems also had properly configured intakes, and weren't starving the exhaust fans for air.

~El~Jefe~ · Post by **~El~Jefe~** » Wed Apr 13, 2005 5:35 am

Q: But I'm building an SLI system with a lot of different hard drives.
A: It's still the same deal. The most amount of power measured from a video card was 76W with the 6800 Ultra at full load with an over clock. Let's round that up to 80 for easier math. You'll get 160W from the video. Now the highest powered AMD processor on the market right now dissipates a maximum of 89W. So between your video cards and processor, you're drawing 250W. Hard drives draw not much more than 30W when they spin up, but once spinning, they only draw about 10W each. That's about it. Most of the other accessories like Sound Card, Ethernet, draw at most 10W and far more likely, just 1W if even that. So with a 6800 Ultra SLI system plus 4 hard drives, you're drawing maybe around 300W total. And if you're actually using 6800GT, drop about 20W per video card, or 260W total. Still think you need a 500W power supply?

If you're STILL not convinced, do the math yourself. I use this source for processor draw, and X-bit lab's article for video power draw. Doing the math yourself is a good idea anyways, especially if you intend to overclock.

Post by **Rusty075** » Wed Apr 13, 2005 6:46 am

Jeff,

Who are you arguing with?

No one in this thread has tried to convince you or anyone else that you need a 500W PSU.

And the other forums threads where people have suggested that they need a high-wattage PSU were dealt with in the same fashion that Tay already told you: Go read the articles. Nothing you've added here is new information, so all you're doing is cluttering up the forum.

Read more, post less.

~El~Jefe~ · Post by **~El~Jefe~** » Wed Apr 13, 2005 7:00 am

Ok, here's why I started this thread. I made a comment on one of the many posts about which psu should i get, thte 50404058560548 watt one or the 430 watt, etc, etc

It was a very small post but was deleted as the forum operater felt that it was going to long and too off topic and sent me this message, which I will not cite who wrote it as it was a personal message. Here's a line or so from it:

"I understand your frustration with people who think they need 500W (I feel it every day), but the thread is supposed to be about Seasonics (and I'm trying to make the thread die ... it's far too long). Of course, I wouldn't object to a new thread about the stupidity of needing 500W. I'd try to make it somewhat constructive though..."

So I tried to make a constructive new post that was geared towards those people who dont ever read (it seems) or maybe not trust the PSU faq on here. This wasnt a post geared towards the more scientific, detailed community.

Bluefront · Post by **Bluefront** » Wed Apr 13, 2005 10:38 am

Jeez....It has been shown often enough that 500w PSUs don't run any hotter than 300w models. So the airflow required to cool them depends on the current draw, and the efficiency of the unit. Which means a 500W PSU can be as quiet as a 300W model.

So who cares what watt PSU anybody gets? Usually the more money you spend on a PSU, the better the PSU. I said usually..... and the more expensive PSUs usually have a higher watt rating.

Like big deal....

StarfishChris · Post by **StarfishChris** » Wed Apr 13, 2005 11:08 am

500W units often come with faster (read: noisier) fans to deal with the extra heat they are capable of generating. At the lowest setting the 300W will certainly be quieter than the 500W.

This isn't a problem if you're doing a fan swap, but then what are you doing with a 500W PSU if you don't need that much?

aaronspink · Post by **aaronspink** » Wed Apr 13, 2005 1:00 pm

~El~Jefe~ wrote:Q: But I'm building an SLI system with a lot of different hard drives.
A: It's still the same deal. The most amount of power measured from a video card was 76W with the 6800 Ultra at full load with an over clock. Let's round that up to 80 for easier math. You'll get 160W from the video. Now the highest powered AMD processor on the market right now dissipates a maximum of 89W. So between your video cards and processor, you're drawing 250W. Hard drives draw not much more than 30W when they spin up, but once spinning, they only draw about 10W each. That's about it. Most of the other accessories like Sound Card, Ethernet, draw at most 10W and far more likely, just 1W if even that. So with a 6800 Ultra SLI system plus 4 hard drives, you're drawing maybe around 300W total. And if you're actually using 6800GT, drop about 20W per video card, or 260W total. Still think you need a 500W power supply?

Processor ~100W peak with an additional 15-20W of DC-DC overhead
Video Card 2x100W
4 Harddrives @ 25W peak or 10W continuous
1 DVDRW @ 25W peak
Motherboard 15-25W
---------------
Baseline total - 405W.
Additional 20% margin - 81W
Targetted power delivery - ~486W.

It isn't all that hard to need a 500W PSU. if you want a very basic system then getting a 250W PSU won't have an issue, but there are a lot of people to are looking for maximisation of performance with a low noise floor.

sthayashi · Post by **sthayashi** » Wed Apr 13, 2005 1:32 pm

aaronspink wrote: Processor ~100W peak with an additional 15-20W of DC-DC overhead
Video Card 2x100W
[...]
Motherboard 15-25W

Where did you get these numbers from?

Kwiet · Post by **Kwiet** » Wed Apr 13, 2005 3:09 pm

I am running a Zalman 400W and most likely less than 200 watts peak. The reason for this is projecting upgrades in the future. Imagine how much power an Athlon 4000+ dual core will pull over a 3000+? Jump my 2 hard drives to 4 or 5, upgrade the video card to ????? and throw a dual tv tuner/HDTV card in to replace the single TV tuner. A 300W PSU should still be able to handle it but what about HOT environments? Say the AC blows out and it is 90F (32C) and the 300W is getting hit by a high load...the fan ramps to full and running loud!

With my 400W, I can have it running cool/quiet even in a hot environment. Having a 500W makes sense if running a 130W dual-core P4 Prescott, Geforce 6800 Ultra, 4GB of RAM, 4 hard drives, burners, drives and a bunch of fans. That type of person could throw a megahot running new video card in 6 months and really pull some power. Who would of thought a video card would pull 76 watts of power 3 years ago?

Solid Snake · Post by **Solid Snake** » Wed Apr 13, 2005 3:30 pm

You mean 4+ monitors?

No, I mean 2 monitors and 1 TV.

~El~Jefe~ · Post by **~El~Jefe~** » Wed Apr 13, 2005 8:28 pm

Kwiet wrote:I am running a Zalman 400W and most likely less than 200 watts peak. The reason for this is projecting upgrades in the future. Imagine how much power an Athlon 4000+ dual core will pull over a 3000+? Jump my 2 hard drives to 4 or 5, upgrade the video card to ????? and throw a dual tv tuner/HDTV card in to replace the single TV tuner. A 300W PSU should still be able to handle it but what about HOT environments? Say the AC blows out and it is 90F (32C) and the 300W is getting hit by a high load...the fan ramps to full and running loud!

With my 400W, I can have it running cool/quiet even in a hot environment. Having a 500W makes sense if running a 130W dual-core P4 Prescott, Geforce 6800 Ultra, 4GB of RAM, 4 hard drives, burners, drives and a bunch of fans. That type of person could throw a megahot running new video card in 6 months and really pull some power. Who would of thought a video card would pull 76 watts of power 3 years ago?

Someone on this thread said heat doesnt change output all THAT much. I thought it did based on spcr testing? Maybe 5-8 degree cline is not that big of a difference, however, a dual core setup with hdtv card, high end vid card and all the drives would.

I think drives heat up things worse than most. They inherently dont have any way to cool themselves and are large masses. I think they slowly build up heat in a large case, based upon experience having very weak (thermally) processors but 6 hardrives making for a roasty case. I think that situation would kill the psu's efficiency.

aaronspink · Post by **aaronspink** » Thu Apr 14, 2005 12:06 am

sthayashi wrote:
aaronspink wrote: Processor ~100W peak with an additional 15-20W of DC-DC overhead
Video Card 2x100W
[...]
Motherboard 15-25W
Where did you get these numbers from?

Processor? 100W is about right for a top of the line processor running a power virus...

6800 Ultra OC 512 will run ~100W min at load.
Motherboard - start adding the power for the various chipsets and you'll hit 15 easily.

tay · Post by **tay** » Thu Apr 14, 2005 5:11 am

First off Hi Aaron, I lurked in comp.arch and beyond3d forums for eons and enjoyed reading your posts (especially in compl.arch).
I think its important to point out that your case is the pathological powersucker case that almost noone hear dreams of reaching for the simple reason that it is not possible to quieten all that. The best you can hope to do is not make it bloody loud.

El Jefe wrote :

I think drives heat up things worse than most. They inherently dont have any way to cool themselves and are large masses. I think they slowly build up heat in a large case, based upon experience having very weak (thermally) processors but 6 hardrives making for a roasty case. I think that situation would kill the psu's efficiency.

Are you implying that the HDs raise the temperature of the case more because they are large masses retaining heat? I dont see it, at the end of the day the same amount of heat enters the case. The only reason 6 harddrives would kill your PSU is at startup using peak power since most controllers dont have staggered boot up.

Why you dont need 500 watts

Why you dont need 500 watts

evacuate the heat role

very clever

Re: Why you dont need 500 watts