yoongkc

How is the calculation for power usage done?

If I buy a 550W power supply, does it mean that my power usage will always be 550W or only if I fully load my PC and used up all the power supply cables? This query has been very headache as I checked with many sales person, but answers are not consistent.

Hope to hear from you guys soon! Thanks!

ceewi1

No, the PC will only use as much power as it needs. If the components you have plugged in only require 200W, the power supply will only supply 200W. 550W is just the maximum the power supply is (theoretically) capable of. You will not use more power by getting a larger power supply.

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fortyways

Also, if you're interested in keeping your power consumption low it's a good idea to get a high efficiency (80+) power supply.

yoongkc

Wow, thanks for the information. Always have the idea that the output power is the stated watts, so if I don't use require that much power, the rest will just be wasting electricity.

Anyway, another question is that, how do we know how much power is drawn? Is there a rough guide or we have to literally add up the stated power drawn on each component, like motherboard, harddisk, DVD writer etc.

diduknowthat

There are some PSU calculators online, but they're very rough. Another thing to look at is how many amps there are on each rail. Beware though, you cannot just add the amps of multiple 12v rails together.

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fortyways

I don't think it works this way. For example, if a manufacturer lists a video card's power requirement as 400W, that's the power requirement for an entire average system with the video card in it. The video card doesn't draw 400W of power on its own.

I wouldn't listen to any salesperson by the way. They'll just try to convince you that you need the biggest and most expensive power supply, lest your computer explode.

Quality is more important than quantity with power supplies.

Praetor

You can use something like this to get overall usage, for major not-retardedly-compelx components like harddrives and such, their power usage is defined in specs, otherwise you're out of luck (short of busting out the electrical gear)

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