connectorpower
I currently have a fan with a 4-pin connector that I want to power, but I do not have a power supply with a 4 or 8-pin connection. Is it possible to disconnect this connector piece and connect the individual wires directly? (red and black?)
Update: I gave it a shot and removed the connector piece and hooked up the red/black wires to a power supply. This worked.
I think you'll find assembling it pretty straightforward when you have the bits in your hand. It's the 'now injection-mould the body' stage which comes next that you'll struggle with.
For a one off repair like this, you can probably do something useful with heatshrink to keep it all together.
Alternatively, cut an existing USB cable in half, and use the 'A' end with some of its attached cable. Then you'll only have to join the cables - another heatshrink job.
There is nothing special about a computer when it comes to leds. You can power directly off the ATX supply (Either 12V, 5V, 3.3V) or from the fan connector (12V). Just add an appropriate resistor and you are done. You need to apply the same led calculations as anything else:
$$Resistance = \frac{Source\,Voltage - LED\,Forward\,Voltage\,Drop}{Desired\,Current}$$
The Fan connectors have three pins, one for 12v, one for Ground, and one for Tach/Speed Sensing.
Since you mentioned cooling, are you talking about 1W or higher LEDs? The same still applies. You could use the fan connector for both a cooling fan, as well as the led power source.
Best Answer
Most fans with a separate PWM-speed-control lead are designed to run at full speed if that lead is left floating. This is a safety measure so that, if the wire comes loose, the system won't overheat due to the fan stopping.
In general, all fans designed for use in PCs use the same wiring. Starting from the black wire, they are Ground/return, +power (almost always 12V but some non-PC fans use other voltages; check the label on the fan), tachometer (wire is grounded by the fan a certain number of times per revolution, usually 2 or 4) and PWM. The PWM wire is always on the end to allow a 4-wire fan to be plugged into a 3-pin connector for either no speed control or PWM control by interrupting the +power pin.
BTW, the link provided in the comment by M. Y., http://pcbheaven.com/wikipages/How_PC_Fans_Work/, with all of its edits, confirms all of this.