Molex 3 pin?

Short answer to the Post above, YES, you can connect your fans to your PSU with those cables.



Quote from an old 2012 Post (Credit to Paperdoc)

Start with: all case fans are deigned to run at 12 VDC for full speed, but will run slower under the right conditions. Details below.

A 4-pin Molex connector from the PSU will supply 12 VDC to the fan at all times over 2 wires, so it always runs at full speed. Such a system has no way for the fan's speed to be sent to the mobo.

One IMPORTANT note: it is advisable to plug your CPU cooler fan into the CPU
_FAN port of your mobo, and let the mobo's automatic systems control the CPU fan speed. This ensures that the CPU cooling fan (assuming it's working properly) will run fast enough to keep the CPU at the right temperature, but not too fast so it makes more noise than necessary. It also allows the mobo to check that the fan is working - it will shut the system down fast if that fan suddenly stops.But because of that checking feature, if you opt to run your CPU fan straight from a Molex PSU connector at full speed, you must tell your mobo's BIOS NOT to watch that fan, or it will get very upset that there is no fan speed signal to watch.

Do NOT plug into the mobo CPU_FAN connector ANY other fan. If you don't plug the CPU fan in there, leave that fan port unused.

A 3-pin fan plugs into EITHER a 3-pin or a 4-pin fan port on the mobo. Fan connectors and the mating mobo ports have been designed, physically and electrically, so that they always will fit together with reasonable electrical connections, but the details of fan speed control are not always the same. If you plug a 3-pin fan into a 3-pin fan port of the mobo and allow the mobo's automatic systems to control the fan speed, here's what happens. The fan's power is on the Black (Ground) and Red (+12 VDC) wires, and the mobo lowers the voltage on the Red wire to reduce fan speed as needed. The Yellow wire carries a pulse train (2 pulses per revolution) signal generated in the fan motor back to the mobo for display and monitoring. This is how the mobo can warn you if the fan stops. The basis for speed control is what's called a feedback loop. In that system, the result of the loop's control action (a measured actual temperature) is fed back into the mobo controller and compared to the target. As the actual temp changes from the target, the control loop changes its output (the voltage supply to the fan) to bring it back to target. Note that the actual measured fan speed is NOT used to control the fan speed - that control is based only on measured temperature. For the CPU, the actual temperature measurement is done with a sensor built into the CPU chip itself and fed to the mobo on one of the CPU's pins. For the Case Fans, the mobo has its own temp sensor built in and uses that to measure the actual inside-the-case temp.

A 4-pin fan plugged into a 4-pin fan mobo port works very similarly, but the details of how the fan speed is controlled are different, and the wire color codes are different, also. In this system, the Ground and +12 VDC power supply lines and the speed pulse return line are all there still, but there's a 4th line carrying the PWM (Pulse Width Modulation) signal. The +12VDC supply line in this system is always at that full voltage (does not get reduced by the controller). Inside the fan motor is a small chip that uses the PWM signal to control how much of the time the +12 VDC supply is actually fed to the motor, effectively reducing the average current flowing through the motor, and thus its speed.

Now, what about "mis-matched" fans and ports? As I said, they will work because of the backwards compatibility designs. BUT ... If you plug a 3-pin fan into a 4-pin port, that fan will receive the first three signals, and not the PWM signal it can't use, anyway. However, the +VDC line is always at +12 VDC on a standard 4-pin port, so the fan always runs at full speed. To handle this situation, SOME mobo makers allow you in BIOS to change the mode of operation for the fan controller for that port, and make it behave like a standard 3-pin port with varying +VDC supply, accomplishing fan speed control. Some mobos even are smart enough to figure this situation all by themselves and make that mode adjustment for you.

Now the other way - a 4-pin fan plugged into a 3-pin port. The fan will receive the first three signals, but no PWM signal to use. So it will not do anything to alter the flow of current from the supply through the motor. But since this is a standard 3-pin port, the +VDC line is varying, not fixed at +12 VDC, so the fan speed CAN be controlled by the mobo.

To complete the picture, SOME mobos have a port labelled "PWR_FAN", and SOME PSU's have a set of wires coming out of them the obviously fit onto a standard 3-pin fan port. If you have both of these, you plug one into the other. All it really does is allow the mobo to receive the PSU fan's speed signal and monitor / display it for you. This mobo port does NOT control the PSU fan's speed. IF that fan's speed is under control, that is entirely done inside the PSU itself. Now, if you do not have such a signal wire set coming out of your PSU, you just don't plug anything into that mobo port. EXCEPT ... some mobos apparently do have the Ground and +12 VDC signals on that port so it CAN be used to power a 3-pin or 4-pin fan, but it will not have any speed control - it will run at full speed at all times.

Too many fans to connect, and not enough mobo ports? Well, you can do a few things to deal with this. First, it appears that most mobo fan ports can supply enough current to power TWO fans per port, but not more. The limit is mainly in the heavy momentary current as the fans start up from stopped. If you are going to strip fan wires and solder them together to accomplish this, note this. For 3-pin fans you should connect together the two Black (Ground) wires, and then the two Red (+VDC) wires. But leave only ONE Yellow (speed pulse) wire connected to the connector - leave the second fan's Yellow wire disconnected. You should not feed two pulse train signals into one fan port - the mobo pulse counting system will get totally confused. If you're doing this with 4-pin fans, follow the same rule, plus tie together the two PWM signal lines - two motors can share use of that signal. Check the web for color coding on 4-pin fans.