More volts + amps and watts

Cecil's Columns/Staff Reports
1

Dear Cecil,

I read an article in a computer magazine the other day which said american cabling also could not deliver enough amps along with (because of?) the low voltage power design so a computer with two high end video cards, an overclocked processor etc would need two separate plugs into the wall to provide the wattage required. Is this true?

Steve

2

No, not even close. If that were true, we wouldn’t be able to use toasters or hair driers, since these can draw upwards of 1000 watts. About the largest personal computer power supply currently available is around 600 watts and that is an absolute maximum rating based on the full load capacity of the supply, not what it’s actually going to draw, even in a fully-loaded computer. I’d be amazed if the peak draw for even a super-high-performance computer much exceeds 300 watts or so.

3

A link to the column is appreciated. It’s How come the U.S. uses 120 volt electricity, not 240 like the rest of the world?

4

How come the U.S. uses 120 volt electricity, not 240 like the rest of the world?

300w power supplies are definately nearing their death…

[url=“http://www.guru3d.com/article/Videocards/391/9/”]

So if you have two of these in an SLI config, a decent dual or quad core processor, ancillaries, your PSU is easily going to need two power plugs surely?

Maybe that’s peak, but what is the relation between voltage, amps and watts?

I know when I did a home buil dI bought a 600 watt psu because they’re supposedly more efficient if they’re providing alot less power than the max rating, and it can handle the peak when I boot the beast with all the other stuff in it (drives, cards etc).

5

For AC circuits, watts is volts times amps times power factor. In most everyday cases, you can get away with saying watts is approximately volts times amps because power factor is normally pretty close to 1, unless you have a very reactive load, like a large motor; but strictly speaking, volts times amps is VA (volt-amps) when you’re dealing with AC. For DC, watts is equal to volts times amps.

6

A normal 15A, 120V receptacle in the US is rated for 120V x 15A = 1800 Watts. Some receptacles (e.g. in a kitchen for a microwave) are rated at 20A, giving 2400 Watts. This should be plenty for PCs in the near future.

Edit - I’m glossing over the watts vs. VA distinction, but the point is that a US receptacle can supply plenty of juice for a PC …

7

These days, new kitchen installations usually have at least one 30-amp circuit. And you can get larger ones should the need arise.

8

Nope. Here’s a 1,000 watt PSU in a standard ATX size that uses only one power cord and is meant to drive things like quad-core and multiple SLI video cards.