Hi!
I just got two PC fans in the mail today, but I have a qustion.
These fans have 4 wires. Positive 12v, Negative 12v, PWN wire and a sense wire.
I've read a bit on the internet about PWM control a PC fan from an arduino, and it's a bit hard to use the PWM wire.
Is it possible to PWM control the fan using only the red (12v+) and black (12v-) wires. Can I just hook the yellow PWM wire to 12v+?
Take a look at Arduino PWM, you could probably use this with the yellow wire or just the red wire too.
hansibull:
Hi!
I just got two PC fans in the mail today, but I have a qustion.
These fans have 4 wires. Positive 12v, Negative 12v, PWN wire and a sense wire.
I've read a bit on the internet about PWM control a PC fan from an arduino, and it's a bit hard to use the PWM wire.
Is it possible to PWM control the fan using only the red (12v+) and black (12v-) wires. Can I just hook the yellow PWM wire to 12v+?
I'm thinking that you should power the fan normally thru the red and black wires and then PWM the PWM wire. That way the tach (sense) output wire will provide an accurate indication of RPM. Once you connect the red and black wires, the fan should run at full speed with the PWM wire floating. You should then be able to PWM the PWM wire.
When I power the fans with only the red and black wire, the fan goes up to full speed, like a regular motor. I hookek up a large capacitor to in parallell to the fans, so I don't get that PWM noise. Is it really necessary to use the yellow wire if the fan works great? I tried to hook the yellow PWM wire to positive DC while the motor was running. The fan seemed to "fight against itself", like it had a separate coil running the other way.
If you wanted to rely on the tach output signal, then yes you would need to use the regular PWM wire. Otherwise you are turning the whole circuit board on and off with the PWM. On a 4-wire fan, the PWM wire is connected internally such that it only turns the fan on and off without depowering the tach output when the motor is in the OFF part of the PWM duty cycle. If you don't care about the tach signal, then do whatever floats your boat. 
I'm going to use these fans inside a DIY amplifier, so the tach is not important, exept for some fancy stats
Thanks a lot! I'm just going to PWM the fans trough the red and black wires.