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Re: DC power supplies
>You guys get the fans from computers, you could also get the power supplies
>from the computers, you can probably find old ones for free from someones
>old Pentium 133 machine. Plus I'm not sure on this but computer power
>supplies deliver a ground
>+12v, +5v, and something else so you may be able to hook up a switch to run
>a fan on the 5 volts to make it slower and quieter and then switch over to
>12volts for when you're at work or something, just a suggestion.
While this sounds tempting, it is not a good idea. Computer power supplies
require a minimum load on the outputs, usually several amps on the +5v
line, and several 10's of milliamps on the +12v line. They are also not
very efficient for use in this way -- using a 200w power supply to run a
(12v * 0.2 A =) 2.4 watt fan isn't very good. The 80-90% efficiencies you
see quoted apply only when the supply is running at 100% load.
Simple wall-wart type plug-in transformers are a much better way to go.
They can be had for cheap and do the job. All electronics
(http://www.allcorp.com) is a good source.
And for that someone who complained about them taking up too much space,
you are not alone. You can get a "wall wart remover" from Musician's Friend
that is basically a short extension cord with a little clip to make the
wall-wart into a "tabletop" type supply. They are a few $ each.