Formula for calculating psu wattage ??

[Soulkeeper]

anyone know the formula they use to calculate the wattage rating of a particular psu ???

 

[Soulkeeper]

ok according to this site RIGHT HERE and a few others you can just use the typical P=IxE formula on each rail and add it up

the problem tho is that all psu's out there don't output the amps they advertise on each rail
if they did their rating would be much higher
for example my antec 480 would be about a 577watt psu
they actually supply much less when maxed out on the proper test machines, not to mention voltage drops also affect the power ratings
but the wattage ratings are valid when all math is done on a maxed out psu like done on that site

interesting, i just wish they would give you the true numbers

 

[Mark R]

There is no formula. The PSU is designed aiming for a particular power capacity.

The individual voltage regulators are designed for a specific current. Then the whole PSU is tested in a laboratory. The power rating is then measured by varying the load while measuring temperature and voltage to ensure that the voltages stay within range and the PSu does not overheat.

 

[DAPUNISHER]

I find this one useful

 

[Soulkeeper]

Originally posted by: Mark R
There is no formula. The PSU is designed aiming for a particular power capacity.

The individual voltage regulators are designed for a specific current. Then the whole PSU is tested in a laboratory. The power rating is then measured by varying the load while measuring temperature and voltage to ensure that the voltages stay within range and the PSu does not overheat.

yeah they do test them.
but they do still use the P=IxE formula

 

[Mark R]

The formula may work, but many PSUs cannot supply maximum power on all rails simultaneously due to the way they work.

For example, in most ATX PSUs the 3.3V line is actually powered from the 5V line. The power ratings of these 2 lines therefore can't be added together to work out the maximum rating of the supply.

Not just that, but all the power in typical supply comes via a single transformer, with a single control system - the maximum rating of this determines the capability of the supply, irrespective of the current capacity of the individual rails.

 

[Soulkeeper]

yeah the formula does work if measured properly
and the antec true power series are supposed to have independent rails unlike many other psu's


thanks for the replies

 

[KF]

>There is no formula.

I'm with Mark R on this.

It is just a rating. Some manufacturers are conservative, some are realistic, some are BSers, some are crooks.

The rating does not represent anything definite. The power supply may continue to supply power just fine at over it's rating if it is well designed, or it may overheat and burst into flames before it gets there if it is one of those $20 400W wonders.

A real professional power supply would have a garanteed rating. They would say how close the voltage is to nominal, with how much ripple, at their garanteed output current. In order to meet that garantee it would have to be designed to exceed that. They would state definately whether all outputs can be used at their maximum continuously (usually not.)

The obstacle to putting out high wattage is the power consumed by the power supply, the power that never makes it to the outside. This wasted power overheats everything. The ferrite cores are too small, the heatsinks are too small, and the fans too weak to get rid of the waste heat if these home power supplies were really to put out 400W.

I would like to see the test conditions under which these home PC supplies get their ratings. There does not appear to be any. I looks like what they do is find the junkiest 230W supply they can find, and then say that if that power supply is a 230, then mine is a 400.

 

[Goi]

I use AMD Builders Guide for Systems (PDF file) if I have to.