http://www.pureoverclock.com/article15.html
Understanding or ?deciphering? the specifications of a power supply and comparing different manufacturers labelling is not a harmonious process. There is no clear industry standard for labelling the specifications of a power supply, nor are there standards in terminology. This means there is no clear way for us consumers to know which power supplies are better than others. One example is power output.
Continuous Output - Measures the ability of a power supply to provide power over an infinite period of time in specific conditions, i.e., at an ambient temperature of 50c.
Peak Output - Measures the ability of a power supply to provide power for a short period of time above its continuous output rating. Peak output should last for no longer than 17 seconds with not more than one occurrence per minute.
Manufacturers do not have to give away the above two specifications as peak or continuous output, they can rename them to imply whatever they may wish. Some unscrupulous manufacturers out there can take serious advantage of this situation.
For example, let?s imagine that one of these deceitful manufacturers has a PSU where the ?total power output? (which genuine power supply manufacturers would list as the continuous output) is rated as 500 watts, but they have listed the peak power output instead. You could be fooled into buying this 500 watt power supply which under continuous output guidelines would probably be rated as 350 watt. They can get away with this because it?s not illegal for them to make up there own terminology to express specifications. In my opinion it?s about time power supply manufacturers were forced to show both continuous and peak outputs and name them as such! This would protect the mainstream consumer from what essentially are false claims.
To show you that this really does go on lets visit a well known power supply manufacturer: Q-TEC is a well known brand that sells a bucket load because people think they are getting a bargain. The link HERE takes you to the specification page of there 550W dual fan PFC model. This power supply is sold and marketed as a 550W unit but on its specification page it states that it can handle 550 watts peak. This power supply is not a real 550W unit.
Because there is no standard in terminology, it is difficult to look at one PSU?s specification as it?s written on the box, and compare it to another. You really need to figure out which numbers are continuous power and which numbers are peak power, but it?s not as easy as you may think?.
It?s time to further explain problems with how specifications of some power supplies are determined. It?s all well and good stating that a power supply can do 500W continuous but unless each manufacturer is testing continuous output under the same testing environment you can once again be fooled into thinking a specific power supply is better than another. When determining continuous output a power supply should be able to operate and maintain running at full load in 50° C (122° F) ambient conditions. This is the variable needed to be used to give a power supply its continuous output rating. Unfortunately, not all power supply manufacturers test under these conditions and so cannot always reach there rated continuous power output.
For example, let?s assume a power supply was rated as capable of 500W continuous output, but was tested at 30c ambient only. On reaching 40 or 50 degree ambient temperatures, you can pretty much guarantee it will no longer be capable of a sustained output of 500W. This is because Capacity diminishes as temperature increases, so your power supplies internals are simply not as efficient when temperature increases. Let?s move on from unscrupulous practices and focus on understanding legitimate power specifications.
In the image below you will notice that this power supply is rated for 510W continuous and 650W peak. This is a PC Power & Cooling unit, they do not fudge there ratings or use unusual terminology.
Let?s add up the Amps of each rail to see what total wattage you come up with. To do this you use the following formula: Voltage x Amperage = Wattage. Adding up all the rails for this unit gives a total of 707W, far beyond its 510W continuous rating. By doing this simple bit of research you can now accurately guess what ratings are continuous or peak output. In this case, commonsense tells you that all the individual rails Amps were listed as peak. But why is it saying 650W peak in the diagram when we just totalled 707W peak?
You'll often find that the capabilities of all the rails combined almost never equal what is listed for each rail individually added together. This is because, though each of the rails are on there own transistors, they share the same primary transformer (coil) and to some extent, rectifiers and filters
For example, let?s assume a power supply has two +12V rails. It?s likely the two rails will share one coil, a secondary transformer. The coil may be rated for around 30 Amps output but the manufacturer branches the two +12V output circuits from the coil. The power diodes (rectifiers) of each circuit may be rated for full load at 19 Amps or so but the coil is still limited to 30 Amps peak. If you draw 19 Amps on the first then you have only 12 Amps for the second circuit. This give and take generally results in current limits for both at around 16-17 Amps before triggering overload protection. The +3.3 & +5 Volt rails generally share the same coil since the voltage is close enough to pick these voltages off the same coil. The +12 Volt output is high enough so that you could not easily build a coil to output all three voltages together. That is why you will see a minimum of two supply side coils in any PC power supply and in power supplies which have four +12V rails, three coils or more.
On average the +12V rail is the most important for a modern PC. Modern GPU?s, motherboards and CPU?s all draw from the +12v line so always pay attention to the +12V rating. Regardless of the overall PSU rating, make sure the +12v rail is large enough for what you need. For high-end systems utilizing one GPU it is recommended to have a power supply capable of 24 amps on the +12v line. For SLI or crossfire systems you should look for over 30 amps as a minimum.
Great artcle lots of good info!!
Facebook
Twitter