Proper Psu for Your System

[mylanta]

I am a rather frequent visitor on another forum and a question comes up often on how to figure the proper psu for your system. The configuarator I have always used usually seems a little low to me on what your system demands and done yesterday it shows me requiring 360 watts and I use a Thermaltake 430 which I feel gives me plenty of running room.
http://www.jscustompcs.com/power_supply/

Another hardware maven produced this configurator, which shows I require 560 watts. Well 200 watts difference between two tests is ridiculous, and I have never seldom seen that much called for, yet the guru sporting this one which she swears by, says it is totally accurate and what she uses in her shop.
http://www.extreme.outervision.com/psucalculator.jsp
What do you guys think here?

[tonyd]

I haven't used these calculators as I haven't ever built a system. However I do want to make a comment using my electrical engineering experiences. Components all have tolerances. Circuit cards, chips, etc will vary in the amount of power required to operate them, especially if they come from different lots.

Also, manufactures will put a safety margin on their specs. For instance, a power supply rated at 250w is supposed to put out at least 250w. It may put out more or may be just marginal.

I remember looking at schematics for car radios to determine which one to purchase. I found 2 radios had the same circuitry with different specs. The one with the better spec had a higher retail price.

Bottom line - use specs as a guideline, but your mileage may vary.
-td

[dbarrow]

I posted a PSU review link a while back ... think it was on Anandtech ... but it may be in the old archives somewhere.

The critical factor was not overall wattage of the unit but the ability to maintain consistent correct line voltages.
There were many surprises in that review ...
Some of the expensive name brand top of the line PSUs showed quite miserable results!

Yes, total wattage is a consideration and top end video cards that require their own external power connection will flat out tell you to have 480w or better ... they suck juice!
Since the introduction of such high end vid cards, we have seen PSUs grow well above the 500w range with many brands now offering 600+.

I would hunt down any reviews where they actually bench tested the PSUs. I know I have read a few.
Remember, the most critical factor is the ability of the PSU to regulate and maintain consistent voltages on all lines.

Very minimal voltage variations, as little as .05v to your CPU, can cause a host of intermittent problems and strange failures that are impossible to track down.
The fact that Windows BSODS when your DVD player spins up may have nothing to do with software or the DVD but a minor voltage drop that undervolts the CPU or ram for the fraction of a second to cause an error.

Many of the larger capacity PSUs now offer swappable plug in main lines (trunk lines with multiple plugs) and 3-4 12v main supply "rails" using these lines.
That can be important to prevent overloading one single supply line where you end up daisy chaining cds, dvds, hds, and a number of fans. Anything with motors can cause a voltage drop when they initially kick in.
The "regulator" inside the PSU is supposed to rapidly adjust to the correct voltage, in milliseconds. The extra main "rails" makes it easier to spread the load or concentrate non-critical items on a line where slight drop outs won't matter.

Some of the more expensive models even have "tunable" regulators and a drive bay face plate with voltage readouts. You can adjust or bump up voltage on a particular line. This can be important if you overclock and have to up CPU and ram voltages.

If you are buying a PSU as a stand alone purchase, hunt down any test reviews. Don't rely on brand name recognition. I would always add extra capacity if you think you may add more hd or fans at a later date.

When buying a case that comes PSU included, lookup the specs! Most cases that come with a PSU usually have the cheapest possible included for the price.

When I built this machine, the case came with a 480 Antec PSU of reasonable quality. I replaced it with a Thermaltake 520 top end model as the first step in building.
It did come in handy as a replacement in my older machine when the PSU crapped out in that and has been performing well in that box.

[mylanta]

I couldn't agree more DB with psu in a case normally being crap, and I never buy them that way.
And "The critical factor was not overall wattage of the unit but the ability to maintain consistent correct line voltages." this is 100% my experience as well.
There is a tendency out there for folks to think that a 500 watt psu will cover all issues, and they spend $19.99 for one and feel safe and of course are in for a rude awakening as quality of psu is so much more important than wattage. Anyone who has seen a cheap one blow out, and take the cpu and motherboard with it knows exactly what I mean.

[kern]

I couldn't agree more DB with psu in a case normally being crap, and I never buy them that way.
And "The critical factor was not overall wattage of the unit but the ability to maintain consistent correct line voltages." this is 100% my experience as well.
There is a tendency out there for folks to think that a 500 watt psu will cover all issues, and they spend $19.99 for one and feel safe and of course are in for a rude awakening as quality of psu is so much more important than wattage. Anyone who has seen a cheap one blow out, and take the cpu and motherboard with it knows exactly what I mean.

...not to mention cheap power supplies usually create electrical interference in sound cards, especially when using a motherboard with integrated audio chip.

[mikehende]

From reading all of this I still don't know which overall wattage to get for a new pc. I understand about looking for the different features in a PSU and about calculating the wattage requirements of each "major" component but how do you account for all of the smaller stuff? Meaning, I jot down the wattage requirement for HD, CD-ROM, DVD e.t.c and add them all up, let's say all of these bigger components add up to 300watts so then should I get a 400, 500 or 600 to cover the rest of the smaller stuff and to have extra power for future add-ons/upgrades?

[mylanta]

Go a little bigger for "surges"...but these days if you buy a 450 decent brand which means Antec, Enermax, or Thermaltake.
Here is a common calculator used:
http://extreme.outervision.com/psucalculator.jsp

[mikehende]

Thanks for the link, someone who used it says it worked for him, will keep it on file!

[mikehende]

Regarding "fans", the book says that the intake is usually located at the bottom of the case, sucking in air and blowing all over the components then the hot air rises and would go out of the pc via another exhaust fan located at the top within the PSU, in my case, I am sensing the "opposite", I took a piece of toilet paper and placed it in front of both fans, the top fan pulls the paper and the bottom one rejects it. Seems to me my pc is intaking the air from the PSU fan at the top and exhausting through the lower fan, can I be correct? How can I tell for sure?

[dbarrow]

The PSU, in particular, should be venting OUT as this is one of the largest heat generators in your system. Yes, I have encountered a PSU with the fan mounted backwards!

In general theory, heat rises, so it is appropriate to have your intakes at the lowest point and exhaust at the highest.

Airflow can be extremely important for all components.
You should make sure that cables, IDE ribbons, ect. are tucked as well out of the way as possible to create the best possible unobstructed circulation.

If your case has a side fan, this should be your intake blowing cool air in as it is usually directed at the vid card, motherboard, and CPU.

It is ok to make front mounted fans exhaust if you have a side intake. This will suck heat off the hard drives and push it out of the case.

Rear fans are generally exhaust to pull heat off the mobo and CPU and exhaust it.

One of the best options is a top mounted "blow hole" fan.
Exhausting directly out of the top keeps hot air accumulating there from being sucked through the PSU keeping it cooler. The difference in overall case temps can be considerable with a top mounted fan.

Of course, I have a solution for really hot days...
A 3200cfm Nutone bathroom exhaust fan mounted in the cool cellar blowing through some ductwork and a 4" flex pipe that connects to the side intake fan on my case with a peanutbutter jar lid. The power switch is on my power console base in front of me.
Also handy for blowing any dust out of the machine!
All my intake is routed through the duct and even if the room gets hot, I am drawing cool air from the basement at all times.
The water cooling makes it kind of redundant but in the summer, when 3d gaming, I need all the cool I can get unless the AC is on.

[mikehende]

The PSU, in particular, should be venting OUT as this is one of the largest heat generators in your system. Yes, I have encountered a PSU with the fan mounted backwards!
.

My pc came straight from Dell brand new so I am guessing this is the way they designed it, the PSU fan cannot be mounted backwards by accident, I think becuase then the lower fan would have to be reversed too. I will try contacting them to see if I am correct and what their reasoning is for this.

[mikehende]

just tried contacting Dell to confirm this fan issue but since my pc is no longer under warranty, they can't answer my question, can this company be any more ridiculous?

[mylanta]

You just found another reason to build your own!

[mikehende]

well yes but it costs money which I don't have right now;), one thing's for sure, as soon as I can afford it, especially with the knowledge I am getting now, i will build my own powerhouse pc.

[tonyd]

Have you tried inserting the AC plug in the other way?

-td

[mikehende]

Have absolutely no idea what you mean here Tonyd? The power plug can only go in one way in the PSU as far as I know.

[tonyd]

Don't worry - it was just a joke - it goes back to my electrical engineering days. Reversing the plug on an AC circuit does nothing to change the system.

I agree with previous posts, the PSU should be venting out because of the heat it generates. Maybe Dell has a better idea?

-td

[mikehende]

If Dell has a better idea then I will have to purchase a new pc from them to get warranty support to get an answer to my question, since I will NEVER buy either a used or new Dell pc in my lifetime, this will have to remain a mystery.

[Dan18960]

Some Dell units vent the psu on the bottom to a "funnel" that gathers the psu and cpu fans heat to an exhaust fan in a central location.

The BMX models did the same thing - which is probably why they had a short life span.

Of course, this is Dell's built in attrition plan to get you to buy a computer every 3 years. :eek:

[athomsfere]

Some PSUs are meant to vent into the case, mine for example.

The PSU can only be attached one way of course, and there is fan that pushes air out the back and another that pushes it into the case, right above the CPU. Directly behind the CPU I have a 120mm fan pulling al the air out, and the case stays cool. (3200 venice OCed to 2.2Ghz, Ram OCed to 336 real clock, stock HSF and CPU and board stays at 32/33 C)

[mikehende]

Good to know my pc is not an "accident", thanks.

[athomsfere]

Your welcome.

Its actually a better idea to vent into the case IMHO.

Alot of people like to stack crap on the tower (I've done it once or twice) and potentially block the airflow, and where could that lead you? A dead PSU.

[casey]

Since my next build will be an AM2 and a faster CPU I was reading about power supplies with interest. I already have the Sata drives I want to use plus the DVDRW drives and floppy. I purchased a 500W Thermaltake from Fry's for $24.99 + $8+. It was $69.99
with a $45 rebate. I also bought a 430W Thermaltake from Newegg for $24.99 after rebate. It was $39.99 with a $15 rebate with free shipping. I'm really starting to like Outpost as they seemed as fast as Newegg. I ordered the PSU's on Wed afternoon and already have the one from Fry's and expect the one from Newegg today.
I only need the Motherboard ( looking at Abit) and a CPU.

[athomsfere]

What are you looking at for Graphics cards?

[casey]

Not really sure right now as I figured on using one that I have in one of the other computers. Will probably make that decision last unless something really good comes up..

[athomsfere]

Great idea, maybe hold off until Direct X 10. Might be the next needed cards.