View Full Version : Power Supply

19-12-2001, 04:14 PM
Can anyone tell me how much power (watts) is actually consumed by a 230 volt 4 amp power supply in a regular desktop computer?

19-12-2001, 05:02 PM
All depends on whats under the lid.

Taken from nz.comp last month:

'a basic 233mmx with 1 x 20 gig 5400rpm ata100 drive (very approximately)
35 watts boot, 23 watts idle.

a dual p3-500 with 3 x 7200 rpm scsi drives, 5 aux fans (very
approximately) 117 watts boot, 94 watts idle.'

19-12-2001, 05:25 PM
The short answer is 'No'.

However, the longer answer is 'It depends'.

The label on the back might says it is rated at 230VAC, 4A. That would mean that it has a 4A fuse.
There might be a label on the PSU box inside the computer calling it (for example) a 330W supply. That is the total of the (volts x maximum amps) -- watts -- of each of the DC supplies it provides. The supplies will not be at their maximum. They supply on demand. The 12V supply will be loaded more as disks start rotating. The 3.3 V (or whatever) CPU supply will go up and down depending on how hard the CPU is working.

There are losses in the conversion. I don't know -- maybe 85-90% efficiency.

But because the current and voltage going in are not exactly in phase, there will be a 'power factor'. This could be 0.7 or 0.8. There are actually two 'power ratings'. A Wattmeter will show one reading, but the actual VA (rms volts x rms amps) will be higher.

At a guess, your supply might use 100 - 300W, while the computer is running. It won't be using 230V x 4A -- 920VA. As part of a computer there will be the amount your monitor and printer use to add, if you are working out how much the power is costing. The power saving modes reduce the amount sharply.

19-12-2001, 05:48 PM
As an approximate guide: AGP=20/30W, PCI=5W, SCSI=20/25W, FDD=5W, NIC=4W, CD-ROM=10/25W, RAM=10W/128MB, 5200rpm IDE HD=5/11W, 7200rpm IDE HD=5/15W, Motherboard=20/30W, 550/600 CPU=30/45W