Hello,

I am about to build my new computer (the last time I did this was about 8 yrs ago) and I have a PSU question.

Does a 600watt psu only draw the current it needs from mains supply, (eg 400 watt) or does it always draw 600 and just supplies what the computer needs. Would I be correct in thinking that running my PC will be like having 10 60w light bulbs on at the same time?

I By the way I have a 600 watt psu and I am going to use regardless of the answer, just would be nice to understand what happens

Thanks

A computer's PSU will only draw as much power as it needs - 600 watts is simply the maximum wattage the manufacture says it will supply before it starts to smoke. It's very rare that anyone ever gets to the maximum wattage of their PSU, unless it isn't suitable for the components they have.

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Thanks for the info,

My PSU is way over my needs but I was advised in the shop its better to have power in reserve just in case / if you ever upgrade. Good to hear it only draws what it needs. The more I think about it, my question was a little silly.

I think it's good to have a higher psu just incase along the road you plan to overclock things.

You guys are on the ball and 100% correct. It is better to have the capability of needing more power, than needing it and not having enough.

Adding devices, changing hardware, upgrading, and power fluxuations all merit having a higher Power Supply unit than needed.

As posted below, Power Supplies only put out what is needed. And the more you add on to your PC, the more power is required.

Good post !!!

Hello

I have taken this as face value that all of this is true, and many others have also noted that this is true including developers etc... However, I have always wondered how much power my rig is drawing, especially my server machine. Our house hold bill is approaching £90 a month, which is rather high, so I may hook up a couple of multimeter's to the power line that all my machines are linked too, and then take an average result, maybe even rig it up through my servers serial port to allow web users to see power consumption. Just an idea.

Although yes, power supplies have a max wattage, the rating e.g. 300W, 400, 500, 600W some go up to 1200W etc... but that is a beast. And the computer only uses what it needs and no more is taken, so none is wasted.

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Take an old line cord, strip the primary insulation and use a clamp-on meter to measure the amps going through the black wire (black, US - Brown in Euro (i think)). Multiply the amps times your volatage to get the watts.

Keep in mind (as mentioned) that the PSU draws what it needs - at that time. Motor loads (HDD, CD-ROM, etc) are less effiecent than electronics so try to have a much running as possible when you take your readings. Play a movie, crank the volume up and start a defrag (all at the same time) to see what your likely to draw at max load.