Let’s pretend i buy a 500 watt power supply for my computer. Does 500 mean the max it can output, -or- does it mean that when i turn on the computer i am pulling 500 watts all the time?
No, the wattage rating is a maximum the supply could deliver, should the demand require it. Under normal conditions, your machine will use far less than the rated maximum.
With QED’s answer, how can i find out what wattage my system requires when everything is running (3 hard drives, CDRW, DVDRW, Athlon XP2.1, GeForce 3 Ti200, nic, blah blah blah)?
I used to be troubled by questions like this, but then I bought a device pn eBay that can make line measurements like instantaneous watt/amp draw; total watts consumed over time; peak, average and minimum voltage; and more. Mine’s called a Kill-a-Watt, and cost $25.
It beats the heck out of a clamp-on ammeter and is more accurate.
Radio Shack started selling this unit shortly before I left. It’ll tell you true watts draw, VA, line voltage, current, and power factor, among other things. Really not a bad little device.
Ok, I think i’m confused. How do i hook up a Kill-a-Watt to my graphics card or hard drive or mouse?
p.s. I am sick so i’m not on top of things today
You can’t do it directly. The Kill-A-Watt only measures the total amount drawn by the power supply (which is what you asked) The individual components are powered by their connectors ow harnesses. In the case of a card, a clamp ammeter wouldn’t help you either.
You can, however, determine individual loads by subtraction. To find out how much your DVD draws, compare current draw when it’s running with current draw when its power connector is unplugged. For some devices, you may have to use a substitute (e.g. for a video card, you may have to remove the card and use either the on-board video or a cheap old card, and settle for an approximation)
Many ports, like mouse, keyboard, USB, etc. have a limited power output, listed in the specs. But it’s rarely enough to matter (though I once had a brand of specialty small format computer whose USB port often couldn’t quite deliver the full USB spec power, due to a undersized internal regulator, and other users found it caused flaky networking performance with a USB NIC)
If it’s on a wire or cable connector, you can use a clamp ammeter, but there are some tricks for using them on a shielded cable.
You can find the current draw for most things inside your computer from the manufacturer’s specs, which are usually available on the internet. You need the technical specs, which can sometimes be a royal pain to find on their web site, but they are usually there. Drives, video cards, and motherboards are usually easy to find. Tracking down the current draw of a mouse or keyboard might be a bit challenging, but those are very low current devices anyway.