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The question is simple - I have a RAMPS 1.4 running Marlin 1.1.9 with the three MOSFETs being used (end, fan, bed), but I'd like to have a couple other Marlin-controlled fans. One of them would be a 4-pin, 6000RPM cooler I got from a dead graphics card. Seeing how it runs perfectly at 12V 350 mA if I keep the control pin disconnected (and ignore the sense pin too, of course), Could I connect 12V and GND directly to the PSU (or RAMPS 12V header) and the CONTROL pin to one of the pwm servo control pins like D11? Or do I need a resistor?

I could add some info about the fan if needed, but it's a FirstD 4-pin, 12V 0.35A fan that can run up to 6000 RPM.

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    $\begingroup$ On a side note: I use a L298N dual H bridge motor driver to drive up to four fans on one PCB using normal 5V PWM pins. That might be an option if you're missing fan mosfet ports but don't have 4-pin fans available for all your needs. $\endgroup$
    – towe
    Mar 28, 2019 at 13:40
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    $\begingroup$ @TobiasWeiß that is a nice solution, but I think I'd go with simple transistor driving if I need to use more than this one fan - i'll test thoroughly, but i don't think there'll be more than 1W of dissipation on them even at rather high PWM speeds. $\endgroup$
    – Matias Gonzalez
    Mar 28, 2019 at 14:39

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Yes, this should work.

According to this 4-pin fan specification, such fans use a 5V PWM signal. You would have to make sure the PWM frequency on the pin you use satisfies that 21-28 kHz range specified in the document.

According to 3.3 and 3.4 in the document, you may not be able to turn the fan off completely when using the PWM input signal.

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    $\begingroup$ Indeed works perfectly. The fan idles at very low RPM, inaudible, and ramps up as soon as a motor is activated (i have it set as a fan for my drivers, since I'll receive my TMC2130's soon). Using these 4-pin fans seems like a good alternative to making a separate fan driver, if you can salvage them from an old PC CPU cooler or something of the sort $\endgroup$
    – Matias Gonzalez
    Mar 29, 2019 at 2:54
  • $\begingroup$ which pin did you use? $\endgroup$
    – jayveesea
    Apr 5, 2022 at 11:29

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