A PC Power supply sizing question.

[Al Dykes]

I have a modern system that's running rock solid. It's a Athlon
system with a gig of memory, 2 optical drives and three fast disks.

I've measured the steady-state power and found it to be 160W/213VA.

What size PSU can I get away with, allowing for startup surge and
nameplate exaguration, etc? FWIW, I try to stick to the good brands.

 

[Rod Speed]

I have a modern system that's running rock solid. It's a Athlon
system with a gig of memory, 2 optical drives and three fast disks.

I've measured the steady-state power and found it to be 160W/213VA.

How did you measure that ?

What size PSU can I get away with, allowing for
startup surge and nameplate exaguration, etc?

There is no way go get from the number above to that.

You have to consider the actual rail loads, particularly the 12V rail with current systems.

 

[Al Dykes]

How did you measure that ?


There is no way go get from the number above to that.

You have to consider the actual rail loads, particularly the 12V rail with current systems.



http://www.p3international.com/products/special/P4400/P4400-CE.html


There is no way go get from the number above to that.

You have to consider the actual rail loads, particularly the 12V rail with current systems.

I can do a rough calculation of the amperage of the major components
and match a power supply with good amps on the appropriate lines once
I've picked a wattage catagory.

Is a PSU that's 2x the wattage enough as long as it puts the amps out
at voltages appropriate for the system parts?

 

[Rod Speed]

http://www.p3international.com/products/special/P4400/P4400-CE.html

Yeah, assumed it was likely something like that when I saw
your later post recommending one of those to someone else.

I can do a rough calculation of the amperage of the major
components and match a power supply with good amps on
the appropriate lines once I've picked a wattage catagory.

You've really got to pick an actual power supply and use its
stated rail currents. You cant really 'pick a wattage category'.

Is a PSU that's 2x the wattage enough as long as it puts
the amps out at voltages appropriate for the system parts?

No, what matters is the load on each rail and what the supply
can supply current wise on each rail. In practice with modern
systems that have a separate 12V connector on the motherboard
is normally just the 12V rail, you can ignore the other rails.

The wattage you measured doesnt really tell you much at
all except what it costs to run that system electricity wise.

 

[philo]

I have a modern system that's running rock solid. It's a Athlon
system with a gig of memory, 2 optical drives and three fast disks.

I've measured the steady-state power and found it to be 160W/213VA.

What size PSU can I get away with, allowing for startup surge and
nameplate exaguration, etc? FWIW, I try to stick to the good brands.

The power consumption you mentioned sounds about right...
I've done a few tests with reasonably accurate test equipment and was
surprised to find that
at idle...the typical PC only consumes about 60 watts (sometimes less)
but under full load is more than double.

The tests I ran did *not* measure instantaneous peaks...which could be
rather high...

so it's always best to leave plenty of room for error...

Play it safe and go with a 400 watt supply.

Also...go with a known-good brand name...Buying a cheapie..will not actually
save you any money!