Computer Power Supply and Switch Wiring Questions

[BrianG]

lol, 25A is certainly overkill, but wouldn't hurt anything. I think you'll find it quite large. The toggle lever is about an inch or so long, and the switch case is rather large. But if you have room, use it.

This is a simple drawing of how to arrange the diodes:



This type of switch is what you need (SPDT center off): http://www.radioshack.com/product/in...uctId=2062486#

If you don't want to be able to turn the fans off at all, don't get the "center off" type (you can only toggle left or right).

If you are controlling only one normal speed fan per switch, any 1A diode will work, such as 1N400x (x is any number), like this: http://www.radioshack.com/product/in...ductId=2036268

If you are controlling multiple fans per switch, or a single high speed fan, use 3A diodes like these: http://www.radioshack.com/product/in...ductId=2062577

If you are controlling multiple high speed fans, I'd go with even larger 6A diodes, like these: http://www.radioshack.com/product/in...ductId=2062591

The 3 diodes as pictured drops ~2.1v total, which means the fans get ~9.9v from a 12v source. Add more or less diodes to suit. Just be aware that if you add too many, the fan may not want to start. Usually, nothing less than ~8v is recommended. Also note that if the motherboard is monitoring the fan speed via the rpm signal wire, reducing the fan speed too much may cause the motherboard to think something is wrong with it. If you are hooking the fan directly to a simple 12v source, this doesn't matter.

You could also use a regulator to get any speed you want, but depending on the number and/or power level of the fans used, heat could be an issue. That's why most (if not all) fan speed controllers use a more complex PWM setup. This could also be made with some 555 timers, but if you are going to get that complex, you might as well just buy a pre-made setup and be done with it.