(Originally posted by forum member shawn1cai: personal opinions expressed in this post do not reflect the opinion of EVGA management, it's members, contractors, or agents)
There has never been so many questions about the power supply unit on this forum. It certainly should not be ignored, since it is the heart of all builds. Here is a personal guide to the power supply unit. I realize
The PSU Thread exists. However, I would like to make deeper information easier to be understood by people (hopefully). I will try to make the guide simple as possible.
1. What is a power supply unit? Also called the PSU for short, the power supply unit in computers converts AC (alternating current) from the wall socket into DC (direct current) that the computer could actually use. It powers everything that is inside your case that does not have a power supply unit by itself (i.e. monitor): motherboard, RAM, hard drive, video card, CPU, fans, input devices, optical drives, coolers, and other add-on cards.
Why is it so important? Obviously, it powers everything. However, because of that, it could kill components, too. Therefore one should take great care in picking one.
Modern power supplies have multiple rails, and they include:
+3.3V
+5V
+12V
-12V
+5VSB
This guide will not cover the different rails in detail, but one should note that the +12V rail should be the first thing a consumer should look with the current standards. It powers almost all of the components of a computer, including, but not limited to the graphics card and CPU. As long as the +12V rail is healthily supplied, a good power supply unit should not have troubles.
2. When buying a power supply unit, what is the first thing to look at? A common misconception about power supplies is wattage. Many think that looking at the wattage alone will be sufficient; that, however, that is not true at all. After one looks at the wattage range of his or her needs, a much better and reliable indication of a good PSU is the ampere (A) rating.
Before I go on further, what is ampere? It is simply a unit of electrical current, precisely the amount of electricity per unit time. With the units given by a PSU, the equation for ampere is simply:
Amperes = Watts/Voltage That is the same as:
Watts = Amperes x Voltage Which is also same as:
Voltage = Watts/Ampere (As one could see, that equation is flexible, and could be used in a variety of ways. We will get to use this equation later.)
However, why is the wattage rating not a good indication on the power supply unit’s power? For one, some companies tend to label with the peak power (which is somewhat like the maximum possible output) instead of continuous power (which is somewhat like the maximum long-term stable output). That is a big difference, sometimes into hundreds of watts.
The other reason (and the more important one) is that it is very subjective. To see why, please go back to the equation:
Amperes = Watts/Voltage According to that, there should be nothing wrong looking just at the wattage. However, one must note that
voltage is subjective. One could see that by the different rails (+3.3V, +12V, +5V, etc.) on the power supply unit.
Therefore, you cannot use the overall combined wattage because it varies from different voltage rails, and does not tell you the distribution of the wattage. Distribution of the power supply unit is crucial to the stability of a computer, and one could see the distribution of a power supply unit by looking at the power supply unit’s amperage.
Here is a comparison of two power supply units for an example. The first power supply unit has a reading of the following:
From this reading, one could see many things. For one, it is rated 600W. Second, it can accept AC input from 100-240Vac. Also, there are 160W going through the +3.3V and the +5V rail combined, as well as 6W on the -12V rail and 12.5V on the +5VSB rail. Most importantly, there are 40A on the +12V rail. Here arises yet another common misconception. Some may just add the +12V rails and say it has 44A.
However, one cannot do that because amperage is not additive.
So, how did the 40A come out? Use the equation Ampere = Watts/Voltage. Here, ampere is unknown, so that will be the variable. However, the combined watts is given for the +12V rail (480W) and so is the voltage (+12V). Therefore, plugging in the numbers, a solvable equation is formed:
Amperage = 480W/12V Solving the equation, amperage is 40A. It is definitely a large amperage rating, and a fairly good power supply unit.
However, something else does not add up at first sight. The combination of 160W, 480W, 6W, and 12.5W does not equal 600W.
This is because that those ratings are the maximum possible output for the rails, or the best they could do. That simply means the rails will give and take from the 600W as one rail needs. (For example, at one moment, the +3.3V and +5V rail may need 160W, so the +12V rails give the 59W it does not need, and gives it to the +3.3V and +5V rail.)
The rails cannot output at maximum power along with the other rails at maximum power all at the same time.
The second power supply unit has the following reading:
This reading, shows more clearly the distinction between maximum output and total power. Following the same procedure, one could see that the +12V rail has about 35.4A (425W/12V) maximum output. (Again, the “Max Output Current” and the “Max Power” are the maximum a rail could output by itself, and not at the same time with the other rails.) Although it is not bad at all, it certainly is not as high as the first power supply unit. That means the first power supply unit could supply more power to the +12V rail when it is needed, (i.e. graphics card, overclocking CPU). Therefore, the first power supply unit is the better choice.
(Note: I skipped looking at the AC Input and the Max Output Current for the +3.3V and the +5V rails, as well as the -12V and +5Vsb rail because they are almost identical for all power supplies units within the same range. Usually, comparing the +12V rail alone is enough. For sake of avoiding copyright infringement, I made these ratings up based on existing ones.)
3. What about connectors? Connectors are definitely something to lookout for. Current power design standard (ATX12V 2.2 / EPS12V 2.91) has a very important revision from some of the older designs: 8-pin 12V CPU connector. If you are building a new computer that has a 8-pin CPU connector, please make sure the power supply unit has a 8-pin CPU connector. If your motherboard does not have a 8-pin CPU connector (honestly, you should be getting a new computer then), make sure your power supply unit contains a 4pin CPU connector or a 4+4pin CPU connector. (
Note: the 8-pin CPU connector is not interchangeable with the PCI-E 8-pin connector.)
The recent introduction of the EVGA X58 Classfied motherboard has brought great attention to power supply units with two 8-pin CPU power connectors. It is a great addition to have, a great addition to use, and at the same time a greatly unnecessary addition for most. Unless you are running a liquid nitrogen bench, aiming for the top 10 in whatever benchmarks there is, chances are you would not need it. This topic will be discussed further later in section seven of this guide.
The PCI-E connector is also very important. Make sure the power supply unit has enough proper connections for current needs or future needs if desired. That means if you have a GTX 295 (which requires one 8-pin PCI-E connector and one 6-pin PCI-E connector), make sure your power supply unit (not only has the sufficient amperage on the +12V rail) has at least one 8-pin PCI-E connector and one 6-pin PCI-E connector. Using a 6-pin PCI-E connector instead of an 8-pin PCI-E connector is dangerous, and may cause your graphic card to fail, if not break. (
Note: PCI-E 6+2-pin connectors work just as well as an 8-pin PCI-E connector. It could work as a 6-pin PCI-E connector as well.)
Of course, other connectors are important as well. Serial ATA connectors determine the limit of the number of Serial ATA devices (i.e. hard drive disk, DVD writers, etc.) one can install in a system. Furthermore, molex connectors will power fans after you run out of fan ports on the motherboard. That will limit the number of fans you could have, as well as other hardware like water-cooling pumps. Although floppy drives are outdated today, some power supply units do have them. Again, the number of floppy drive power connectors determines how many floppy drives you could have.
4. What are other things to look for when searching for a power supply unit? Believe it or not, the weight of a power supply unit is usually a good indication of a power supply unit’s quality and capability. From personal experiences, a better power supply unit (i.e. Corsair 450VX) weighs much heavier than a inferior specimen (i.e. FSP Group 450W).
Also, efficiency is a good measure of quality. High efficiency not only mean lower power bills, but also means that the power supply unit creates less heat, which could mean a more quiet and cool working environment for the computer. However, do not be fooled. Sometimes, efficient ratings are skewed. For example, some ratings are around 80% (which is excellent) at 20 degrees Celsius. That is an absolutely worthless measurement because rarely can a power supply unit run at 20 degrees Celsius (with the exception of labs and freezers). Not only that, efficiency is not constant. When a power supply unit is rated at 80% efficient at 90% load, it cannot achieve the save efficiency when it is at, for example, 30% load.
Another thing to watch out for is ripple and resistance. Lower of both is better. Since they are difficult to measure and require special testing equipments, look for good reviews to find out their ripple and resistance. (A great review and informational site dedicated to power supply units is
jonnyGURU.com.)
When possible, try to buy a power supply unit with active power factor correction (PFC). Compared to passive PFC, it is much simpler to use, and is also much better at handling power from the wall socket to the computer. Power supply units with passive PFC will need the user to manually set the input (the little red switch in the back), and do not fully utilize the power from the wall socket. (Most of the good power supplies have active PFC)
There seems to be a high view about SLI approved or Crossfire approved power supplies units. The bottom line is, they do not tell much about the power supply unit. These labels could simply be ignored when looking at a power supply unit.
People argue about single and multiple +12V rails. However, that is very trivial as long as you follow the previous methods and brands (mentioned next).
Finally, following brands is a good decision to make when buying power supplies. Good brands on my personal list include Corsair, Seasonic, Antec, Thermaltake, OCZ, Silverstone, PC Power & Cooling, and Cooler Master. (Like within all companies, there are good and bad. Not
all supplies from the companies are good; just most. Remember to follow the previous tips to avoid getting bad models. Remember to aim at the higher models when looking at Cooler Master and Antec.)
5. How can you know how much power you need? Although the power supply unit finder at SLI Zone could be used (and it does work), it usually makes a consumer buy more than that is needed (which is not a bad thing). There are other calculators that one could use.
A personal favorite is the
Outer Vision eXtreme Power Supply Calculator Lite. Even though it is free, it is invaluable with the option it gives. With it, you can find the most you set-up may take even at 100% load, with a variety of hardware options that are constantly updated.
6. Other Facts
You may ignore this section if you want. This is just a number of trivial things I would like to say. Power supply is not the same as power supply unit. (I’m guilty of using it interchangeably as well.) Power supply is simply the source of power. The power supply unit is the box in your computer that converts and supplies the power.
That aside, power supplies seems to be changing very quickly. As confirmed, EVGA will release a very good power supply unit very soon that has two 8-pin CPU connectors. As power supply units advances, this guide will hopefully be updated by myself or replaced with another guide.
7. Miscellaneous (This section will be updated as I remind myself of more things.)
Common practices involve unplugging and re-plugging the connectors when double checking connections. However, that will increase the chance of corrosion (even though that is something that most people do not have to worry about). Therefore, instead of unplugging and re-plugging connectors, simply checking if the connectors are snug is a far better way to check connections.
As some of you may know already, Antec released a new line of power supply units several months ago, called the CP series. Although the design and quality are fantastic, the power supply units do not abide by the current ATX size format. Instead, it belongs with what Antec calls the "CPX form factor", a exclusive form factor by Antec. Therefore, they will
not fit in most enclosures available. Only the Antec Twelve Hundred, P183, and P193 are compatible.
April 10, 2009 -
The recent introduction of the EVGA X58 Classfied motherboard has brought great attention and desire for two 8-pin CPU power connectors. It is completely optional, and it is not needed for a successful boot-up. (This means it is okay to run the system containing the X58 Classified with one of the two 8-pin CPU power connectors empty.) This feature is probably not needed by the majority of the consumers, as it is designed for extreme overclocking (i.e. liquid nitrogen benching, Shimano, K|ngp|n, etc.) The extra 8-pin CPU power connector gives extra power to the heavily clocked CPU to provide more stability under such extremely high frequencies. However, if you absolutely must have two 8-pin CPU power connectors with your EVGA X58 Classified, here is a list (in alphabetical order) of good power supply units with two 8-pin (or 4+4-pin) CPU power connectors:
(Note: Added 29 June 2010: The PC Power&Cooling models, as they are no longer premium due to OCZ's new ownership (most of their original models are discontinued.) The new PC Power&Cooling, with its re-adaptation of old names (Silencer), is nowhere near the original.
BFG model removed by request of the original poster
Cooler Master UCP RS900-AAAAA3 900W
Cooler Master UCP RSB00-AAAAA3 1100W
Corsair CMPSU-1000HX 1000W M
§ Enermax REVOLUTION85+ ERV850EWT 850W
§ Enermax REVOLUTION85+ ERV950EWT 950W
§ Enermax REVOLUTION85+ ERV1050EWT 1050W
§ PC Power & Cooling PPCT1200ESA 1200W
¤ PC Power & Cooling T12W 1200W
Silverstone SST-DA1200 1200W
§ Silverstone SST-ST1000-NV 1000W
§ Silverstone SST-ST1200 1200W
§ Silverstone SST-ZM1200M 1200W
§ Silverstone SST-ZU1200M 1200W
§ Thermaltake Toughpower W0132RU 1000W
§ Thermaltake Toughpower W0133RU 1200W
§ Thermaltake Toughpower W0155RU 1000W
Thermaltake Toughpower W0156RU 1200W
Xigmatek HC NRP-HC1001 1000W
§ Xigmatek MC NRP-MC851 850W
§ (Added on June 29, 2010)
Corsair AX1200 §
Corsair AX850 §
Corsair AX750 §
Enermax Galaxy Evo 1250W §
Enermax Modu 87+ 700W §
Enermax Modu 87+ 800W §
Seasonic X750 §
Seasonic X650 §
Silverstone Strider 1500W §
Silverstone Strider Plus 600W §
Silverstone Strider Plus 750W §
Silverstone Strider Plus 850W §
Silverstone Strider Plus 1000W §
Notes:
§ This power supply unit is modular.
¤ This power supply unit is ESA approved, and has ESA features. To utilize these features, one must use an ESA compliant motherboard. Click
here to learn more about ESA.
If you have two 8-pin CPU power connectors, by all means, use it. It definitely will not hurt.
8. Further Reading How To Calculate which PSU is good for you:
http://forums.evga.comarchive/tm.asp?m=728603 Time for a new PSU? Supply Squealing!:
http://forums.evga.comarchive/tm.asp?m=709616 How to check PSU voltages:
http://forums.evga.comarchive/tm.asp?m=100633965 Need a new PSU? Read this first!:
http://forums.evga.comarchive/tm.asp?m=100557126 Finding your real PSU Manufacture Guide:
http://forums.evga.comarchive/tm.asp?m=100789470 June 16, 2009 -
Added comments on abnormal Antec power supply unit size standards, under section seven.
August 17, 2009 - Added section eight.
November 16, 2009 re-edited section 8 content
post edited by rjohnson11 - 2012/07/31 23:15:40