looking for a variable resistor or something similar

[Ford Freak]

I would like the output range to be ~5v to 12 using a 12v input. It also needs to be able to handle 3 amps minimum.

[rjs735]

http://www.the12volt.com/ohm/page2.asp

You might start here. You really didn't give enough info.

[Ford Freak]

Did you edit that post or what? I thought I saw something earlier about something with .5 ohm 50w wire. I can't remember the exact details or who posted it.

As for more details, I'm not exactly sure what you want. I am using it to control a fan though. I am also thinking about a multi position switch with a bunch of resistors but I would rather have a variable one since it would be easier to do what I want to do.

[sumrtym]

One word...rheostat.

[rjs735]

I did edit the post primarily I got to thinking that if the power sources gets overloaded with the current drain from the rheostat then you may burnout the PS.

So I instead sent you to the OHMs laws site where you can figure out what you would need.

I would rather you calculate what you need then I give you something and then when the PS burns then you can only blame yourself.

A selector switch with a resistor that changes the voltage to the fan is fine as long as the motor doesn't overheat at either the higher or lower speeds.

Thats basically how yor multi speed a/c -heating fan in your car works.

[KingTermite]

pot => Potentiometer

[moregolf]

Sorry, didn't read the entire post. You can get schematics at fanbus.com.

[sandman55]

You havent given much detail is This what your looking for

EDIT: The current isnt what you first mentioned do you want to control the speed of your computer fans

[Ford Freak]

I only need to control one fan. I am putting a Delta 120 in the side to blow on the RAM and MOSFETS.

[Sierra_abx]

You need something like this:

http://www.sidewindercomputers.com/rheosformc.html

[Ford Freak]

That is what I need. That one doesn't meet the power needs of a 190cfm 120mm Delta though.

[Sierra_abx]

You might want to email Sidewinder Computers. They specialize in Delta fans. They might be able to tell you where you can get the correct rheostat, or, they might even make one for you.

http://www.sidewindercomputers.com/info.html

[Centurion]

I'd check out Mouser or Newark to see what they have in terms of power rheostats. You could probably find something there that will work or use it in conjuction with a voltage divider network. Keep in mind though that 36 watts (12V@3A) for a resistive device will generate quite a bit of heat of its own. Imagine putting a 30 watt lightbulb in your case...