Hello everyone,
I connected four 2-pin DC 5 volt fans in parallel to my Arduino Uno via a mosfet BOJACK IRF3205. With PWM I can control the fan speed as normal. But if I only let them run at 120 instead of the full 255, for example, the fans beep. I then increased the frequency to 31300 Hz on PIN3 of the Arduino. But now only 1 fan is running, but as desired more slowly and without beeping.
How do I get all 4 fans to run? Thanks!!
Please ignore IR:
Use a logic level MOSFET.
Make sure your fan power supply can provide the load current.
But is the MOSFET powerful? 
Yes. But... I suggest a 10k resistor from I/O pin to GND and a serial resistor between I/O pin and Gate.
Short update: I ordered an Logic Mosfet and it doesn’t work also..
I had a look on this case: PC Fan not responding to high frequency PWM
@cogitare8 Could you tell me what you have done to get it work? What are your exact components and program code?
Thank you!
Have you verified that your power source can run all these fans without any other circuitry?
You first.
Try decreasing PWM to 30 Herz.
4-pin PC fans are meant to be PWM-ed with 25kHz (Intel specs), but 2-pin or 3-pin fans not.
They usually work better at frequencies below or hearing range.
Leo..
How much current (Amps) does each fan require? Where is your 5 volt supply coming from?
If I try 30 Hertz, the fans make a "tack" sound, but still running all as expected.
Data of the fans:
Brushless; DC; 5V; 0,25A; 2-Pins
Data of my power supply:
DC5V~2000mA
My new MOSFET:
IRLZ34N
In the attachment you can see my actual code and setup. With this setup, actually only 1 fan is running as expected with 150 pwm.
Thank you for your help!
Yep, some 'knocking' is the expected behaviour at 30Hz.
Don't expect things to be perfect when you're PWM-ing fans that are not made for that.
Leo..
If this doesn't come to a solution, I will use 30Hz or try also below and live with it 
Maybe someone else has more ideas?
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