Curse

Lurid · May 11, 2006, 03:06 AM // 03:06

In my opinion, power supplies are the most important aspect of the comptuter. These hard working units are almost always the least considered part of a system. This is a guide that I wrote, just now, to help clear up some common misconseptions (sp?) about power supplies, and to better inform the community on how to choose a power supply.

Table of Contents

Section 1. What they do...
Section 2. How they do it...
Section 3. Terminology...
Section 4. Choosing one....
Section 5. Explanations of various types...
Section 6. Points to consider....
Section 7. Common misconceptions....
Section 8. Rail Fluxation Testing
Section 9. Do not trust these....
Section 10. My reccomendations....
Credits

Section 1. What they do....

Power supplies convert Alternating Current (AC) to Direct Current (DC) for use in computers, and other electronic devices. Power supplies are judged by some decisive factors, for example:

The amount of current, amperage, and voltage they can supply.
The period of time in which they can supply this amount.
How stably that this amount can be supplied, under varying load conditions.

Section 2. How they do it...

Power supplies use an array of transformers, diodes, and other filters convert and smooth out the voltage ripples. Thus converting AC, into a more stable, "cleaner" form that we call DC, for use in most electronics. There are various types of wall outlets, and other strange power supplies, that most of us will never use, and thus I don't really feel its necessary to cover them in more than passing detail.

Section 3. Terminology...

Wattage - Voltage times Amperage equals Wattage. Wattage is the ability to do work; it can be converted into Horse Power. A PS’s wattage rating is the total combined wattage output of all the rails combined. Older ATX designs created most of their wattage in the +3.3 & +5V rails, creating very little on the +12V rail. Newer ATX12V & ATX12 V2.0 designs are creating ever more wattage on the +12V rail, to meet the needs of our computers. The wattage should never be used to select a power supply, but that the properly allocated wattage is very important in selecting the proper power supply.

Hold Up Time - The ability of the PSU to supply power w/o power being supplied to the PSU, as in the case of a brown out. Measured in miliseconds.

Efficiency and Temperature: There are no electronic devices that are 100% efficient & PS’s are no exception. Typically PS’s operate between 60% and 70% efficiency. The more efficient the PS, the less power that is lost as heat and the lower the cooling requirements. Newer PSU's meeting the ATX12V 2.xx specs have efficiency ratings from 70% to as high as 85%.

Section 4. Choosing one....

Choosing a power supply should not be something you take lightly. Almost always the power supply that comes with a case, is an insufficent POS. Most case manufacturers use third party manufacturers to produce lowered cost power supplies, that do little more in alot of cases than run the fans. Most of them shouldn't even be trusted to do this. One and honestly the only exception that comes to mind is Antec, their case w/ PSU bundles are actually quite good.

Do not rely on wattage, companies can use different formulas to figure total power in watts, and often pump up the more unused rails to make the PSU seem more powerful than it really is. The three rails of ATX 12v power supplies, in order of most important to least important are below:

12v Rail - Powers CPU, some GPU's and motherboard. Most important, explained in detail later.

5.5v Rail - Powers most peripherals, and some GPU's. Important, though less so.

3.3v Rail - Powers smaller peripherals such as fans, floppy drives etc.... No real reason to have an exceptionally beefy 3.3v rail.

Amperage is where its at people, disregard that stupid misconception that wattage matters. Just as easily as a company can say a PSU is more powerful than it really is, they can say that one is less powerful than it is. This is because of alittle thing we like to call voltage fluxation. This fluxuation occurs in a variety of situations, an aging PSU, various temperature ranges, various load ranges, etc....

By saying a power supply is less powerful (in wattage) they are able to gaurantee a steady and stable supply of power, without saying the power supply is more powerful than it is on its worst day, insuring clean, stable, dependable power throughout the unit's life.

Section 5. Explanations of various types...

Single 12v Rail - I reccomend these whenever possible, a single beefy 12v rail eliminates the confusing that accompanies multiple 12v rails. As in the combination of total amperage of both rails to establish the peak amperage, which isn't just adding up the two rails, there is much more involved. These are especially important for Intel based rigs, as their CPU's pull alot of power, especially when under full load and when overclocked.

Dual 12v Rail - Electrical isolation for noise and improved voltage regulation. Some devices, usually electromechanical ones having motors, produce noise spikes & voltage fluxuations, these can include pumps, compressors, fans, drives, lights (when turned on & off) and probably TEC’s & Peltiers. By putting these “noisy” devices, that often turn on & off, or at least often change their power (amperage) demands, on a separate rail we isolate them from the MoBo, CPU, Video Card(s) and the other electronic components that are sensitive to noise & sudden changes in voltage. This is a good thing! ATX12 V2.0 is the future.

Multiple 12v Rails - Often "industrial" PSU's will offer 3 - 4+ rails, alot of peopel think this is a good idea. Which it is...if your running a huge monster server. For you and me its a horrible idea. As power supplies function the best when the power drawing loads are distributed, so that they can equally power everything. When you have 3 - 4+ rails, you must have a massive amount of current / amperage being drawn from each rail to have the power supply function in an anywhere near efficient way. Much much more than any normal computer draws.

Section 6. Points to consider....

Fan size - This fan is the thing cooling the PSU, larger fans are ideal as they cool more effectively and are generally less noisy.

Maximum Amperage Drawn - By using a power calculator, like this one you can calculate the wattage / amperage you are most likely to use. I suggest going alittle overboard though.

Amperage Reccomendations -

AMD 12v Rail = 18A Minimum Reccomended = 26A, 5.5v Rail Minimum = 35A Reccomended = 40A, 3.3v Minimum = 28A Reccomended = 32A

Intel 12v Rail = 20A Minimum Reccomended = 26A+, 5.5 Rail Minimum = 35A Reccomended = 40A, 3.3v Minimum = 28A Reccomended = 32A

Section 7. Common misconceptions....

Wattage - Just because a PSU is 500w doesn't mean it will run all systems well. Depending on the amperage allocation and other factors that 500w PSU may be absolutely stomped by an efficient 400w.

Looks - Flashy PSU's aren't usually a good idea, as in most things flashy usually transfers to cheaply made.

The case PSU is good enough.... - I will refer to one of my favorite photoshop images, ever for this one.Here
is said image.

Section 8. Testing PSU Rails

Companies sometimes lie about the true voltage coming from their power supplies. Do not, under any circumstances, no matter who tells you to do this, ever, trust software voltage readings. The only real way to do this is with a digital multimeter.

WARNING = This is tested while the PC is running, in various stages of startup and load conditions, this is the only way to get an accurate measurment of rails and their fluxuation. This is generally not dangerous, but I like to take every precaution.

Instructions:

1. Get a digital multimeter picture

2. Set the dial to the DC side at 20, this will allow you to test your PSU's rails.

3. Turn off the PC, open the case. Locate the AUX connector and a spare 4 pin molex. Images are here

4. Set up the probes in these locations before you start up the PC.

12v Rail testing image here Directions = Insert the red probe into the yellow 12v connector, and the black probe into any black ground connector on the molex.

5.5 Rail testing image
here Directions = Insert the red probe into the red 5v connector, and the black probe into any black ground connector on the molex.

3.3 Rail Testing Using the AUX Connector Imagehere Directions = Insert the red probe into either one of the two orange 3.3v connectors on the AUX connector
Insert the black probe into any of the black ground connectors on the AUX connector, or the 4-pin Molex connector.

Fluxation Levels chart here.

Testing times:

- POST
- Boot
- Windows Startup
- System at Idle
- System at Load
- Shutting Down

I reccomend replacing a PSU as soon as possible if its near the maximum fluctuation at any time.

Also, it is impossible to safely test the current or amperage of a PSU with out extensive electronics knowlage, and a much more sensitive multimeter, in short do not attempt unless you either have these, or if you are willing to risk your hardware and possibly your life.

Section 9. Do not trust these....

This is not a perfect list, rather a list of PSU manufacturer's that I go out of my way to avoid, from previous horrible experiences.

1. Powermax
2. PowMax
3. Thermaltake
4. Aspire
5. Hi Pro
6. ASUS
7. Raidmax
8. Logisys
9. Kingwin
10. MSI

Section 10. My reccomendations....

1. PC Power and Cooling
2. OCZ
3. Antec
4. Enermax
5. Seasonic

Credits
David Hammock and The Cleaner from Extreme Overclocking Forums, whose intelligent and insightful research and compilations allowed me to learn almost everything that I know, about power supplies.

This is ever changing, and will be updated based upon popular demand, images soon in coming, along with a more expanded guide for each topic and more, as long as the community wishes me to do so. To my knowladge all of the above information is factual, if not please correct me.

This is in no way the work of anyone not listed images have been credited to their respective owners. All information is my intellectual property, and under no circumstances to be reproduced in any form without my consent. I am in no way responsible for what you do to your computer, and to yourself, if you choose to use any of the above ideas you do so at your own disgression, and in no way hold me liable for any damages you may or may not incur.

R A C · May 11, 2006, 04:00 AM // 04:00

Good guide. It certainly taught me more about PSU. I liked the breakdown of recommended reail amperages. That was something I had no idea about!
My previous knowledge was limited to: case/psu combo=bad unless psu manufacturer is good. And also that more watts = better.

Lurid · May 11, 2006, 04:08 AM // 04:08

Thank you very much, as always feedback is much appreciated. Hopefully with some expanding it can be used as an outlet for general power supply information. I tried to encompass as much as I could within my limited range of knowlage

Blade Rez · May 11, 2006, 10:25 PM // 22:25

Good guide, I included something a little less indepth on my guide. What I disagree with is Thermaltake being a bad company. First off their 680W psu sucked, because of the incorrect Rail Amperage. However, their lower psus such as 430W and 500W(some) are decent. BTW you forgot Hiper for Good list hehehh.

Yeah, gj pointing out the fact that Wattage has almost absoluetely nothing to do with the quality, I mean why do u think a Shuttel 350w can run 2 7800gtxs an fx60 2 raptors raid-0, etc?

Narada · May 11, 2006, 10:39 PM // 22:39

Another great guide... man you're really crankin' these things out. Great content, I like how some sections really get down to the nitty gritty.

I wouldn't recommend that DMM though... good picture, but I'd avoid important diagnostics tools that they sell at Walmart for under $20.00 US (I have one.) A quality multimeter will always be expensive, but accuracy, quality, and life of the product are things that come along with that. Of course if you're not one to do heavy electronics work a cheapy will work fine, there's no reason to buy something crazy expensive if you're only going to use it once in a blue moon.

Something that you might want to add about the DMM though... make sure that the probe leads are connected to the multimeter using the correct holes before using them on your computer. Going out and buying a DMM, even if it's a cheapy, only to watch sparks come from the leads and possibly fry your meter is no fun.