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I'm deciding between a 500 watt PSU and a 600 watt PSU.

I currently have a 460 watt PSU that powers everything but my dvd drive, spare hard drive, and 2 fans.

I've determined 40 watts is enough to power my hard drive (approx 15 watts) and my DVD drive (approx 25 watts). Please correct me if these are bad estimates.

So my question is about case fans. What wattage do they generally use? I can't find this information on newegg hardware specs, or by inspecting the fans themselves. I don't have their boxes anymore.

Also I noticed that these power supplies only increase their amperage for the 5 and 12 volt outputs. Would fans be using only the 3.3 volt output? Would in increase in total wattage for the PSU even matter if i'm only adding fans?

thanks.

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great answers, thanks. i'll buy the 600 as it's only 10 dollars more. –  robertpateii Aug 24 '10 at 1:23

2 Answers 2

up vote 4 down vote accepted

Case fans usually use 1.8 Watts and are rated at 12 Volts. The molex connector that is usually used on the case fans is 12 Volts by standard (same as your Hard Drive and Optical Drives usually use). Unless you are adding 50 fans I doubt you have to worry about the power supply. You will be fine with the 500 Watt PSU.

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While I agree with this answer, I would like to add that you need to be careful with some very large fans (say bigger than 20cm). I've seen such fans which use as much as 1.5A of current. –  AndrejaKo Aug 23 '10 at 23:19
    
@AndrejaKo 12 V times 1.5 A is only 18 W. –  Cees Timmerman Jul 21 at 18:17
    
@Cees Timmerman Indeed! That's 18 W per fan. Multiple fans and optimistically rated power supply can produce very interesting results, especially of the rest of the computer is hungry as well. –  AndrejaKo Jul 21 at 20:53
    
@AndrejaKo Are you referring to usage spikes like this 400W one of an 8x4.2GHz Turbo? That might be useful info to add to the answer. –  Cees Timmerman Jul 22 at 0:22

Also, be sure of the type of connector ... not all use molex, some use 3-pin to the mobo. But overall, I agree with the 500W PSU. Be sure to plan for the future as well ... any high-end graphics or high-end audio coming? These can draw up 200W peak (and more if you SLI/Crossfire) ... nothing more frustrating than having to keep upgrading the PSU. Good luck!

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