Watts on pc power supply and other devices

[ChrisGreece52]

Hello i have a question when a pc supply says 800watts for example???
i have seen that on most devices and i have this question please help .
Thank you.

[Monkeh]

Are you going to ask a question?

[dr.diesel]

Not sure I understand the question?  Watts in a resistive load is Voltages * Amps.

[ChrisGreece52]

My question is what does the wattage writen on a pc power supply or home appliances mean

[Monkeh]

My question is what does the wattage writen on a pc power supply or home appliances mean

It means that's the amount of power it's specified to draw or provide.

[ChrisGreece52]

Not sure I understand the question?  Watts in a resistive load is Voltages * Amps.

Sorry for the misleading question ... the thing is that i started understanding some stuff but the thing is that i dont know what they mean for example if a pc power supply has 800 watts of power what does that mean?

[dr.diesel]

See reply #4.

[Monkeh]

Plus http://en.wikipedia.org/wiki/Watt

If you have further questions, direct them to whoever hires the teachers at your school.

[mariush]

A PC power supply takes power from the mains (220-240v 50 Hz in Europe) and produces DC power in various voltages for the components in the computer.

Computers use nowadays 3.3v , 5v and 12v.

A power supply that says 800w on it, is capable in theory of providing up to 800 watts on the cables going to the computer components.

The power supply can deliver an amount of current on each of those voltages, by multiplying the number of Amps (the current) with the voltage, you get the amount of watts the power supply can provide on that voltage

Voltage x Current = Watts

For example, here's a power supply label:



This is a 430w power supply but if you check the label carefully, you can see the power supply is basically 4 power supplies in one:

* 5v Sb (stand by power)  5v  x 3 A = 15w
* -12v  x 0.8A = 9.6w  (legacy, serial ports etc)
* 12v x 32 A  = 384w   (cpu, video cards, motherboard, hdd motors)

* 3.3v and 5v  - 110w in total, but if one is used less, the other one can provide more current

** 3.3v x 20A = 66w   -  but again, max 110w in total
** 5v x 20 A = 100w  /

Further, you can see 110w (3.3v + 5v)  + 384w (12v)  is 494w , which is more than 430w. 
This power supply says on the label, you can't use both 3.3v+5v AND 12v to the maximum, it can only do in total 430 watts. This is perfectly OK for the current computers, because most of the power used in today's computers is 12v (about 80% or more)

Also, it doesn't mean 430 watts of power are constantly consumed by the computer, it's an "UP TO THAT AMOUNT" value, it means that the power supply can take power from the mains and produce those voltages as long as the components connect to it don't exceed those current values.

If you plug too many things on the power supply and the components use more than 32A on 12v, the power supply is not guaranteed to be able to output 12v or will shut down.

Now keep in mind a lot of cheap power supplies actually lie on the label and advertise a high number of watts while in reality they can only do much less.

This is because most people that would buy such cheap power supplies will also have cheap computers which don't use a lot of power, usually under 200 watts, so they can make power supplies that blow up if the components want more than 300-350 watts and advertise the power supply as 500-600 watts because few customers would actually have such power hungry computers.

[ChrisGreece52]

Plus http://en.wikipedia.org/wiki/Watt

If you have further questions, direct them to whoever hires the teachers at your school.

Sorry man but we are talking about GREECE !!! the most sucky educational system in europe where the teachers are trying really hard to teach but the ******* stracture of the educational system crushes under its own weight.
So the only way to learn its wikipedia
because
1)most subjects are completely useless (Ancient Greek( i love the roots of my language and i also respect this lesson verry much but the grammar kicks my butt), literature (mostly meaningles poems from unknown artists NOT good literature like Dante or Shakespear) A subject about Christianic religion (which is useless in a polytheistic country and because most students believe different things of many (so am I) are atheists ) )
2)messed up book content / bad writen books
3)LONG ..... LONG and mostly bad combined schedule.
So its NOT my fault i want only to learn stuff.

[ChrisGreece52]

See reply #4.

Thank you.

[ChrisGreece52]

A PC power supply takes power from the mains (220-240v 50 Hz in Europe) and produces DC power in various voltages for the components in the computer.

Computers use nowadays 3.3v , 5v and 12v.

A power supply that says 800w on it, is capable in theory of providing up to 800 watts on the cables going to the computer components.

The power supply can deliver an amount of current on each of those voltages, by multiplying the number of Amps (the current) with the voltage, you get the amount of watts the power supply can provide on that voltage

Voltage x Current = Watts

For example, here's a power supply label:



This is a 430w power supply but if you check the label carefully, you can see the power supply is basically 4 power supplies in one:

* 5v Sb (stand by power)  5v  x 3 A = 15w
* -12v  x 0.8A = 9.6w  (legacy, serial ports etc)
* 12v x 32 A  = 384w   (cpu, video cards, motherboard, hdd motors)

* 3.3v and 5v  - 110w in total, but if one is used less, the other one can provide more current

** 3.3v x 20A = 66w   -  but again, max 110w in total
** 5v x 20 A = 100w  /

Further, you can see 110w (3.3v + 5v)  + 384w (12v)  is 494w , which is more than 430w. 
This power supply says on the label, you can't use both 3.3v+5v AND 12v to the maximum, it can only do in total 430 watts. This is perfectly OK for the current computers, because most of the power used in today's computers is 12v (about 80% or more)

Also, it doesn't mean 430 watts of power are constantly consumed by the computer, it's an "UP TO THAT AMOUNT" value, it means that the power supply can take power from the mains and produce those voltages as long as the components connect to it don't exceed those current values.

If you plug too many things on the power supply and the components use more than 32A on 12v, the power supply is not guaranteed to be able to output 12v or will shut down.

Now keep in mind a lot of cheap power supplies actually lie on the label and advertise a high number of watts while in reality they can only do much less.

This is because most people that would buy such cheap power supplies will also have cheap computers which don't use a lot of power, usually under 200 watts, so they can make power supplies that blow up if the components want more than 300-350 watts and advertise the power supply as 500-600 watts because few customers would actually have such power hungry computers.

THANK YOU
finally what i needed a perfect example
(i also thanks the other members that posted their answer and i will read the wiki article)
but thanks all of you.